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Mr. Widget
05-29-2005, 01:33 AM
As most all of you know Zilch has been working on a variety of 2-way designs using a variety of JBL compression drivers and CD horns for his "Quick and Dirty 4430" thread. Today we spent a few hours comparing five CD horns and six different JBL compression drivers. We set them up and took quasi-anechoic measurements with Clio.

We used the following horns:

1) PT-F1010 - 100° X 100°, 6.5" X 12"
2) PT-H1010, 100° X 100°, 12" square
3) PT-F64, 60° X 40°, 6.5" X 12"
4) SF-95, (Sound Factor), 90° X 50°, 1" thread-on throat, 6.5" X 12"
5) P-Audio PH-230, 100° X 100°, 2342 Clone, 1" bolt-on throat, 9" Square

And we used these drivers:

1) 435Be 3" Beryllium Diaphragm 1.5" exit from JBL Consumer
2) 2435HPL 3" Beryllium Diaphragm 1.5" exit
3) 2431 3" Aluminum Diaphragm 1.5" exit
4) 2418 1.75" Titanium Diaphragm 1" exit
5) 2426 1.75" Titanium Diaphragm 1" exit
6) LE85 1.75" Aluminum Diaphragm 1" exit

Mr. Widget
05-29-2005, 01:34 AM
Before we began our horn comparisons we wanted to explore the low end capabilities of the 2431 and 2435HPL compression drivers with their small back cap and compare them to the 435Be with it's large back cap. To do this we mounted the three drivers on a 500Hz 1.5" throat horn I have that is about the size of an Altec 511. It is not a CD horn so it's on-axis response is reasonably flat without compensation.

Here we see that the low end performance of the 435Be, 2435HPL, and 2431 are all quite good. It would seem that the larger back cap isn't necessary for performance below 1000Hz. We did not do any listening tests or power tests measuring distortion, but the initial measurements were surprisingly encouraging. I am not sure if it is due to the back cap or other tweaks, but the 435Be did exhibit, albeit by a small margin, the flattest overall response of the three.

Mr. Widget
05-29-2005, 01:40 AM
Next we tried the 2431 on both the PT-F1010 and PT-H1010 horns. We have included the plot of the 2431 on the large horn to show how the LF limiting is due to these smaller horns. Also since these are CD horns they would need passive or active EQ to compensate for the HF fall off.

Mr. Widget
05-29-2005, 01:44 AM
Next we tried the 2435HPL on the PT-F1010 horn. We left the 2431 plot up for comparison. We also plotted a second 2435HPL. This one (Shown in Green) seems to be defective... perhaps why it was available inexpensively on eBay?

Mr. Widget
05-29-2005, 01:49 AM
Next we tried 4 different 2431 drivers on the PT-H1010. Zilch has one pair (Green and Purple) that were purchased about a year ago, and another pair (Red and Blue) that were purchased recently. Each pair seems closely matched... but the two pairs do seem a bit different from each other. Perhaps there was a slight design change between the two runs?

Mr. Widget
05-29-2005, 01:54 AM
Next we tried the PT-F64. Here we have kept the plot of the 2431 on the PT-H1010 for comparison with the plots of the 2431 and 2435HPL both on the PT-F64. This horn is much deeper that the other in this test and while stile considered a CD horn, it obviously need far less compensation... at least below 9KHz.

Mr. Widget
05-29-2005, 02:06 AM
Next we tried the remarkably inexpensive SF-95 horn. In the photo it looks a bit like the PT-F64, but it is a 1" horn instead of a 1.5" horn, not quite as deep, and made of an inexpensive plastic. Here we compare the 2431 on the PT-F1010 with the 2418 on the PT-F64. We measured two examples of this very economical driver and horn combination... they were surprisingly similar in performance. Surprising that such inexpensive drivers would be so precisely manufactured.

Mr. Widget
05-29-2005, 02:08 AM
Next we mounted a 2426 driver onto the SF-95 horn to see if the 9500Hz suck-out is due to the horn or the driver. We see that there is no suck-out with the 2426.

Mr. Widget
05-29-2005, 02:12 AM
Here we compared the 2431 on the PT-F1010, with a 2426 and adapter and LE85 and adapter all on the PT-F1010.

Mr. Widget
05-29-2005, 02:15 AM
Finally we mounted the 2418 on a P-Audio PH-230. Here it is compared to the 2418 mounted to a SF-95.

Mr. Widget
05-29-2005, 02:50 AM
Kind of hard to make any definitive conclusions. It would seem that the PT-F1010 was the best CD horn of this bunch in that it had the smoothest downward slope. It is too bad that it doesn't allow for a crossover below about 1.2KHz. I suppose we should have compared it to the H9800 just for grins. I hope this data helps others on their audio journeys.

Widget

Guido
05-29-2005, 04:50 AM
Thank you so much Zilch and Widget :applaud:

I've a question regarding post #9:

Does it mean that the 2431 is
5 dB more sensitive than the 2426 and
3 dB more sensitive thean the LE85 ?

Titanium Dome
05-29-2005, 05:01 AM
Looks like you guys had a fun day. :yes:

Thanks for sharing. :bouncy:

I've often wondered how the 1" Bi-Radial horn on the larger SVAs would fare in such a comparison.

Steve Gonzales
05-29-2005, 09:38 AM
This is a very enlightening thread, thank you both for your time and for sharing the info.

Zilch
05-29-2005, 09:54 AM
Here's my commentary, while the work is still fresh. We haven't sorted it all out yet, but there were some surprises:

Post #2: The size of the back cap is not the big deal with respect to low-end response we thought it was, at least insofar as frequency response is concerned. Whether the smaller-can 2431 and 2435 sound any good below 1 kHz is another matter. On an appropriate horn, they'll at least play down there.

Post #3: Driven by 2431H, the performance of PT-F rectangular and PT-H square waveguides is virtually identical. PT-H plays a little lower, perhaps; it'd take a statistical study to distinguish them, most likely.

Post #4: We don't find a HF extension performance advantage with Be diaphragm (and $1000 premium cost) 2435HPL. As suspected, one of them is defective. They're both going back to JBL for warranty repair.

Post #5: Confirms my feeling that JBL is making design and/or manufacturing improvements on 2431H. Performance above 12 kHz appears "chaotic," but they all play similarly there on RTA. Newer ones are better in HF extension. About 15 dB of compensation is required to make them flat to 20 kHz on PT-F waveguides.

Post #6: For those desiring a narrow sound field, PT-F64 may be the ticket. Remarkably flat up to ~9 kHz, they play lower, too.

Post #7: The "economy" Ti-diaphragm 90° X 50° combo, it sounds good with proper compensation, actually. PT-H95 is available for 1.5" exit drivers, but the PT-F version of this "preferred" pattern is only prototypes thus far, alas.

Post #8: Hmmmm. Gonna have to see if it sounds better, too. Another economy alternative, though I'd want to support the much heavier 2426 driver independently. That is one cheap horn, for certain. There's also a SRX 90° X 50° horn for 1.5" drivers that might be worth looking at:

http://www.jblproservice.com/pdf/SRX700%20Series/SRX712M.pdf.

Post #9: We think the adapter is responsible for the bumps in the FR. Actually, two adapters are required to mate the LE85 with PT waveguides. Still, as you may know, it's my favorite-sounding combo of "vintage" drivers. I play it with 3110A crossover for compensation.

Post #10: PH-230 is P-Audio's inexpensive 2342 clone. It'd take polar studies to determine if it's worth a whit for constant directivity. The real thing is still available, tho....

Steve Gonzales
05-29-2005, 10:14 AM
Do you think the larger backcap will make the difference when some real world power tests are made?. (My) Not having much knowledge of these types of tests (the ones you've already run), is it your experience, that a driver can exhibit an ability to play below it's FS ( 900hz- 2435HPL) and still perform with good, usable output, in a real world installation, crossed over below it's recommended 1.1k?. In other words, are the people that own 2435HPL's to assume that it is okay to cross them over at 800hz?

Mr. Widget
05-29-2005, 10:41 AM
Interesting questions... we should have run an impedance sweep on the 2435HPL and 435Be with both the large horn and one of Zilch's smaller horns.

Zilch, if you bring driver #6 back over here we could run that test as well as run the distortion test.

Widget

Zilch
05-29-2005, 10:49 AM
I'm compiling a new measurement list. :D

I want to try 2431H and 2435HPL on H9800, as well, now.

And 2431H on PT-F with our crossover for it.

We also have a 2430H on the way for evaluation.

Note to readers: We have a JBL UHF driver study on the docket here, too - 2402, 2403, 2404H, 2404H-1, and 2405....

Mr. Widget
05-29-2005, 10:55 AM
I've a question regarding post #9:

Does it mean that the 2431 is
5 dB more sensitive than the 2426 and
3 dB more sensitive thean the LE85 ?

Yes, in this comparison. Thanks for pointing that out, I meant to address it but forgot. I believe the drivers are all inherantly very similar in their sensitivity, but for us to compare these three drivers on the PT-F1010, both of the 1" drivers required adapters. I believe these adapters are responsible for the lower output as well as the undulating response seen in the Blue and Green plots. I assume that due to the physical offset of the LE85 vs. the 2426, it's sensitivity was less affected.

Steve Gonzales
05-29-2005, 10:56 AM
Looking forward to the results! :D

Mr. Widget
05-29-2005, 11:11 AM
Post #4: We don't find a HF extension performance advantage with Be diaphragm (and $1000 premium cost) 2435HPL.

True. I'd like to point out that one of Zilch's goals is to find a combo that will eliminate the need for a tweeter. I am not sure if any of these combos are a stand out in that regard.

I would say that looking over these plots the most expensive drivers, the 435Be, and the 2435HPL have the most linear output through most of their range. This to me is significantly more important than extension, but all of these components are only parts of a system. It is up to us as designers to determine how best to use their capabilities.

If I were going to pursue a project with any of these combos, I'd take these plots into consideration but I'd make my final determination based on a series of subjective listening evaluations.

Widget

Titanium Dome
05-29-2005, 11:36 AM
True. I'd like to point out that one of Zilch's goals is to find a combo that will eliminate the need for a tweeter. I am not sure if any of these combos are a stand out in that regard.


Widget

Aha! I wondered if that was in the back of someone's mind. :hmm:

johnaec
05-29-2005, 06:26 PM
Note to readers: We have a JBL UHF driver study on the docket here, too - 2402, 2403, 2404H, 2404H-1, and 2405....I like to help on that one if it'd fill things out. I can bring an "H" structure, an unused 2405 dia, and an unused 2405H. I say unused even though they're new - they've been new in the box for 15-20 years...(does that affect these types of dias?).

I could also bring an 035Ti and 035TiA for comparison purposes.

John

Zilch
05-29-2005, 07:39 PM
What I suggested to Mr. Widget:

"Let's hold off on the tweeter project until John can come help."

:D

[We had PLENTY on the plate with the mids/waveguides....]

johnaec
05-29-2005, 08:11 PM
"Let's hold off on the tweeter project until John can come help."Just give me a little notice if you can... ;)

John

Mr. Widget
05-29-2005, 08:40 PM
Here is a comparison between the 2431 mounted on the PT-F1010 and the K2-S9800 mid driver and horn used full range. (435Be driver on the H9800 horn) The K2 combo was better on the lower end, as it should be since it was designed to operate down to 800Hz. It was also smoother all the way to 15KHz. To me the most impressive thing was the unit to unit consistency of these premium products. The Blue plot is from one 435Be on one H9800 and the Green plot is another 435Be on a separate H9800. They were identical in performance between 600Hz and 15KHz +/- 0.32 dB!!!

Widget

Mr. Widget
06-16-2005, 11:34 PM
Before we began our horn comparisons we wanted to explore the low end capabilities of the 2431 and 2435HPL compression drivers with their small back cap and compare them to the 435Be with it's large back cap. To do this we mounted the three drivers on a 500Hz 1.5" throat horn I have that is about the size of an Altec 511. It is not a CD horn so it's on-axis response is reasonably flat without compensation.

Here we see that the low end performance of the 435Be, 2435HPL, and 2431 are all quite good. It would seem that the larger back cap isn't necessary for performance below 1000Hz. We did not do any listening tests or power tests measuring distortion, but the initial measurements were surprisingly encouraging. I am not sure if it is due to the back cap or other tweaks, but the 435Be did exhibit, albeit by a small margin, the flattest overall response of the three.

I reposted this post to bring us back to the topic of the low end performance of the 2431, 2435, and 435Be.

Widget

Mr. Widget
06-16-2005, 11:41 PM
Here is a post of the 435Be back on the large horn. We drove the driver to a fairly loud sounding 95dB (we had our fingers in out ears as the stepped sine wave screeched) to measure the second and third harmonic distortion levels. The distortion levels were raised by 30dB. The second harmonic is at a fairly low level, and the third is 60dB down through the usable portion of the spectrum.

Mr. Widget
06-16-2005, 11:43 PM
Here is a plot of Zilch's "better" 2435HPL. We are not sure what the specs are for distortion, but this unit has significantly more third harmonic distortion that the 435Be.

Mr. Widget
06-16-2005, 11:46 PM
Here is a plot of the 2431. Again we aren't sure if this is within specs, but the distortion is significantly greater than the 435Be. Hopefully we can get them tested by JBL and then we can measure them again to see if these plots are indicative of their performance. When we measured this driver we heard a noticeable buzzing sound as the frequency swept through the lower frequencies.

Mr. Widget
06-16-2005, 11:49 PM
Here are the impedance plots of the three drivers all mounted on the same horn. They are all definitely 8 ohm drivers.

Widget

Guido
06-17-2005, 03:27 AM
Thanks for that info!

Well it seems that the larger backcap reduce distortion. But we should wait for the JBL inspection on Zilchs drivers.
Personally I think it's a shame that we have new JBL drivers here and can't be sure if they are according spec! :(

Earl K
06-17-2005, 03:59 AM
Very Interesting,
Thanks guys, for all the effort put into this !

- I would have loved to see a distortion plot generated for the heavier diaphragmed 2430. I would think it should have a bit less 3rd Harmonic than the 2431 or 2435.
( Would also have loved to see how the Altec 288-8K measures up in the distortion department )


Well it seems that the larger backcap reduce distortion.

- My initial guess would be that the higher distortion specs (for the 2431 & 2435 ) are due to the lack of aquaplas on their light-weight diaphragms / an underdamped situation, perhaps . ( Just showing my personal bias again for proper mechanical dampening )


:cheers:

johnaec
06-17-2005, 05:31 AM
Here is a plot of the 2431. Again we aren't sure if this is within specs, but the distortion is significantly greater than the 435Be.Widget - I thought when you ran the distortion curves for the 2431 that they weren't plotted at the same -30 offset. In the plots you posted, the 2431 distortion curves don't look as bad as I remembered them looking during the tests...

John

Zilch
06-17-2005, 11:05 AM
Personally I think it's a shame that we have new JBL drivers here and can't be sure if they are according spec! :(The 2435's were purchased on eBay, provenance indeterminate. The were used, but the price was right, especially if JBL's 5-year warranty applies....


In the plots you posted, the 2431 distortion curves don't look as bad as I remembered them looking during the tests....They look pretty nasty below 800 Hz there. They were buzzin' at the lower frequencies. In retrospect, I think we should start at 500 Hz, not 100 Hz, with power tests on compression drivers. It does not seem to have harmed them, tho....


I would have loved to see a distortion plot generated for the heavier diaphragmed 2430. I would think it should have a bit less 3rd Harmonic than the 2431 or 2435.There's supposed to be one on the way for testing. I'll follow up on that....

Mr. Widget
06-17-2005, 11:05 AM
Widget - I thought when you ran the distortion curves for the 2431 that they weren't plotted at the same -30 offset. In the plots you posted, the 2431 distortion curves don't look as bad as I remembered them looking during the tests...

JohnNo, that's what we ran... it must have been the shock of seeing all that green on the monitor that made it seem even worse. The fact is second harmonic distortion is much harder to hear so a bit of it isn't a problem. Third harmonic distortion sounds definitely wrong and should be as far down as possible. On most of the plots I have seen third harmonic distortion is well below second, but here on the 2431 it is about the same as the second and on the 2435 it is even higher than the second in places. Typically manufacturers only raise their distortion curves by 20dB, so these curves will "look" worse than other published curves.

Two points here. The 2431 driver and the 435Be are "new" drivers that were shipped from JBL. The 2435 was an eBay purchase so the fact that it's higher distortion is rather suspect.

Widget

Mr. Widget
06-17-2005, 11:11 AM
"They look pretty nasty below 800 Hz there. They were buzzin' at the lower frequencies. In retrospect, I think we should start at 500 Hz, not 100 Hz, with power tests on compression drivers. It does not seem to have harmed them, tho...."

With the cap we had on them they were -3dB at ~400Hz and we were feeding them milliwatts. I am quite sure it was safe. I think these particular drivers are not meant to be used at those lower frequencies and hence the distortion.

That is what we were doing after all... seeing how they perform at lower frequencies.


Widget

Zilch
06-17-2005, 11:20 AM
That is what we were doing after all... seeing how they perform at lower frequencies.Yeah, some members wanna use them on BIG horns! :p

Perspective: 2425/6/7, LE85, 2420, etc. diaphragms are 1.75" diameter. These are 3".

Maybe I open up that 2431H and make sure everything is tight in there.... ;)

grumpy
06-17-2005, 11:24 AM
might the buzzing sound simply be a misaligned diaphragm voice coil (vs. actual
mechanical damage)? the procedures for installing new diaphragms suggest that some
"5lb alignment tool" tweaking is the norm. Mostly curious, as diaphragms I've installed
have passed through the suggested sweep without issue thus far (properly cleaned and
gaps checked, etc...), but I don't have experience with newer JBL compression drivers.

If I followed right (no guarantee there), JBL is or will be looking at the unit in question?
It would be nice if they also provided a diagnosis of the "failure".

-grumpy

edit: or just being used outside design/intended range...as suggested.

Mr. Widget
06-17-2005, 11:26 AM
Yeah, some members wanna use them on BIG horns! :p

Perspective: 2425/6/7, LE85, 2420, etc. diaphragms are 1.75" diameter. These are 3".


These are also not general purpose drivers like the LE85(2420) and 2425/2426. The 435Be was specifically designed for the H9800 horn in the K2-S9800 system and these others were designed to be compact and lightweight in specific PA arrays. Just because they have 3" diaphragms doesn't mean that they will perform as well as the general purpose drivers outside of their design range.

I think we need to send in the 2431 and 2435s to JBL and have them look at them before we can come to any conclusions.

Widget

Zilch
06-17-2005, 05:08 PM
2435HPL's went back to JBL today.

[Wishin', hopin', n' a-prayin'....] :p

Guido
06-18-2005, 01:05 PM
2435HPL's went back to JBL today.

[Wishin', hopin', n' a-prayin'....] :p

Yeah, let the waiting begin..

Sorry Zilch couldn't resist :D

B&KMan
06-19-2005, 05:15 PM
Dear Mr. Widget and zilch,


Superbe jobs and very thanks for all precous times test for evaluation driver and horn...

the manys responses test and THD curve is expose many critical information...

thanks again...

:applaud:


for more deterministic test it is interesting to expose test response in many angle ??? ( 0°, 15° and 30° )

this test is expose a important aspect of quality of driver...

2--- it is interesting to expose more parameters experiences: rectangle pulse, distance mic etc...


Thanks for all big works and give at this communauty...

:)

whgeiger
06-22-2005, 05:41 PM
To All,



Only a PWT load will provide a rational means for measuring driver performance. Otherwise, what is being measured is a combined driver/horn response dominated by horn artifacts at the frequency extremes; i.e.:



1) When the test signal frequency approaches horn [fc], the driver becomes un-loaded while at the same time the horn mouth becomes acoustically small and the intensity of the resulting back-waves that impinge on the diaphragm is increased. This leads to erratic diaphragm excursions even though the drive signal may be relatively small.



2) On axis response and power response are different animals. In the former, beaming of horn output hides roll-off at the upper end; so, here again horn influence is masking driver capabilities.



Regards,



WHG

Mr. Widget
06-22-2005, 05:51 PM
True.

However what we were attempting to do was compare the 435Be with it's large back cap with these similar drivers. We chose this particular horn because it has a [fc] below 500Hz which is well below the frequency range we were interested in. I would agree that a plane wave tube would be ideal, but since we don't have one, and a home brewed PWT would only add to the questions, I am quite happy with the results of our comparisons. Once we have verified drivers to test we should be able to come to some reasonable conclusions. These will be relative conclusions between these drivers, not idealized conclusions.

Widget

edgewound
06-22-2005, 05:58 PM
...and it's also nice to know that the drivers are actually working right before you test them, to get any meaningful results, i.e. no rubs or buzzes.


Edgewound

whgeiger
06-23-2005, 07:24 AM
True.
However what we were attempting to do was compare the 435Be with it's large back cap with these similar drivers. We chose this particular horn because it has a [fc] below 500Hz which is well below the frequency range we were interested in. I would agree that a plane wave tube would be ideal, but since we don't have one, and a home brewed PWT would only add to the questions, I am quite happy with the results of our comparisons. Once we have verified drivers to test we should be able to come to some reasonable conclusions. These will be relative conclusions between these drivers, not idealized conclusions.
Widget

WW,

1) A PWT is relatively easy to make. See AES documents [1] & [2] for details. Presuming you already have a microphone and test gear, the cost of materials to make it is less than $100 and it should take no more than a weekend to fabricate. While the acoustics of each tube will be slightly different, that difference unlike the horn, will not materially affect measurement validity, particularly when such data is used for the purposes of comparative analysis.

2) All comparisons are intrinsically “relative”, and in this case, need to be based on reliable and objective data. There is a difference between prerequisite and “ideal”; for valid comparisons to be made, first reliable measurements must be obtained. When using a horn as a test jig, this is not happening; e.g., horn artifacts, at the bottom end, are manifesting themselves as distortion products due to the driver being operated below the horn’s effective pass band, which begins at least one to two octaves above horn [fc].

Regards,

WHG

References:
[1] Title: Plane-Wave Tubes: Design and Practice
Author: AES Standards Committee
Publication: AES-ID, No. 1id-1991, Rev. Jun-2003
URL: http://www.aes.org/standards/b_pub/aes-1id-1991-r2003.pdf
Abstract: In section 2.2.1 of the "AES Recommended Practice — Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement" calls for the use of plane-wave tube to perform measurements of horn drivers. Because many variations and results are possible, depending on the details of construction of plane-wave tubes, this document discusses those variations for the purpose of encouraging further experimentation.

[2] File: ASAJ047-0596
Title: Building a Plane-Wave Tube: Experimental and Theoretical Aspects
Author: Roberto Magalotti
Author: Carlo Zuccatti
Author: Paolo Pasini 596
Publication: AES-J, Vol. 47, No. 7/8, p. 596, Jul/Aug-1999
Abstract: The primary purpose of this report is to describe the building and testing of a plane-wave tube for measuring compression drivers in an audio laboratory. A new method for testing the tube for undesired reflections was devised, with and without sound absorbing materials. The experimental results show good agreement with the predicted behavior outlined in the AES document on plane-wave tubes, and confirm the predictions on usable bandwidth limits.

Mr. Widget
06-23-2005, 10:06 AM
"When using a horn as a test jig, this is not happening; e.g., horn artifacts, at the bottom end, are manifesting themselves as distortion products due to the driver being operated below the horn’s effective pass band, which begins at least one to two octaves above horn [fc]."

I thought we discussed this already. The point is, those artifacts will affect all of these drivers in the same manner. Since our purpose wasn't to determine the absolute value for each driver but rather the relative performance between them, I think you are going over board. Of course if you would like to make us a PWT, I'll be happy to use it in future tests. It would be nice to have one for 1", 1.5", and 2" drivers.

Widget

BTW: your link didn't work... I did try to check it out.

B&KMan
06-23-2005, 10:26 AM
BTW: your link didn't work... I did try to check it out.
[/size][/font]

It is not work for me too...

after manys try on site to pass in other way I realize this information is sale on this site...

(...)

Jean.

BTW this very interesting informations...

:applaud:

Steve Schell
06-23-2005, 11:15 AM
I have been experimenting with plane wave tubes for the past few months. I was unhampered by knowledge in my first attempt, and stretched 8' lengths of 2" plastic plumbing pipe all across the back yard. Despite progressive stuffing in the line, there were a series of monster peaks and dips in the response.

Next a friend obtained information from a U.S. manufacturer on their plane wave tube construction techniques. They recommended a 6' tube, mic hole very near the driver, and a long tapered wedge of open cell foam stuffing beginning immediately past the microphone. This advice yielded a tube that works very well.

More recently I read the AES article, and now understand more about how these devices work. The article recommends that the smallest diameter tube be used to push a transverse mode cancellation to the highest frequency possible, extending the reliable bandwidth of the measurements.

Plane wave tube measurements can tell you a lot about driver performance in a short time, without the flattery of the high frequency beaming of most horns. The measurements in a tube flatter the low end response, though, as the loading is so much better than in any real world horn. Most compression drivers look like awesome subwoofer drivers on a PWT, with response down only 6dB at 10Hz. or similar.

Guido
06-23-2005, 01:47 PM
Plane wave tube measurements can tell you a lot about driver performance in a short time, without the flattery of the high frequency beaming of most horns..

OK, and then?
We need a Horn with all its flattery high frequency beaming. To tweak the crossovers we now need to measure the horn/driver combo. Bingo, back where we started.

Steve Schell
06-23-2005, 05:22 PM
I see your point Guido, but the desirability of high frequency beaming is open to debate. A horn that steers into a progressively narrower beam at high frequencies will sound and measure well directly on axis, but the off axis radiation that largely creates the reverberant field will be noticeably dull in comparison. I believe that our brains can detect this descrepancy easily, adding another artifact that creates a reproduced, rather than live sound. This may be one reason why conical flare horns tend to sound so uncolored, as they vary little in response over their entire pattern.

Plane wave testing is useful to isolate out the driver's power response from horn effects, making it possible to compare drivers on an even footing. I agree completely that it is also necessary to test a given driver on the horn it will be used with, as we don't listen to them on plane wave tubes!

Mr. Widget
06-23-2005, 05:31 PM
A point I'd like to add is that the conical wave guides you speak of are not the conically shaped horns like the JBL HL91 (2307/2308). These horns are exponential and do progressively beam higher and higher frequencies, as do dome and cone transducers.

The conical wave guides you are discussing are similar to JBL's Bi-radials in that they have a falling on axis response that achieves (in theory at least) an even power distribution and will have flat frequency response off axis as well as on axis if EQ is added. Unlike JBL's Bi-radials the conicals do not have the secondary acoustic center and are therefore claimed to have a better sense of realism and imaging.

Widget

Earl K
06-23-2005, 06:04 PM
Okay, since I'm about to go offline for about a month or so, I thought I better reiterate my sincere "Thank-You" to Mr. Widget, Zilch , Johnaec, and all the rest of the crowd who participate in putting these newer ( & older ) JBL Pro products through their paces .

For those not aware; these R & D efforts are done at these fellows own expense ( time and money ) , and I for one, really appreciate the huge efforts being made to peel back the mystery surrounding these products. These guys unselfishly publish their findings and I want it known , I really appreciate it ! ;)

Since I find myself as a user of JBLs' "off the shelf" products / what these guys have done is "spot on" for my needs ( and I would guess for most of the people who frequent this forum ) .

Again ; Thanks Guys ! <. Earl K :applaud:

Zilch
06-23-2005, 06:30 PM
To be precise, it's the DRIVER that has the falling power response, not the horn, and the horn geometry either "corrects" it by differential steering, as in exponentials, or it does not, and must be EQ'd flat, as in most Biradials and other constant directivity designs, or some intermediate compromise in between.

The little OASR horn we studied is termed a "conical waveguide" by JBL. Is that an example of the conical under discussion here? Looking again, there's no apparent throat constriction to perform diffusion; the shape itself confers constant directivity. If so, I'm gonna hook it up and listen some more. :)

[I NEED to pay better attention, quite obviously....]

Zilch
06-23-2005, 06:36 PM
Again ; Thanks Guys !You and everyone are welcome, of course. We're "driven" by relentless inquisition is what.... :D

Mr. Widget
06-23-2005, 06:38 PM
To be precise, it's the DRIVER that...

Yeah, yeah, sure, sure... I was talking in terms of them working as a system, but yes, you are correct.;)

I have to admit, I haven't paid much attention to the OASRs, but yes, if JBL is calling them conical wave guides, then yes that is what Steve is referring to. Do they make any with a lower cut off? These had a pretty limiting bandwidth.

Widget

Zilch
06-23-2005, 06:47 PM
I have to admit, I haven't paid much attention to the OASRs, but yes, if JBL is calling them conical wave guides, then yes that is what Steve is referring to. Do they make any with a lower cut off?They make some rectangular versions that may qualify. Lemme look....

2352 (630 - 18 kHz) and 2392 (300 - 4 kHz) series, looks like:

http://www.jblpro.com/pub/technote/tn_v1n21.pdf

http://www.jblpro.com/pages/components/23525354.htm

http://www.jblpro.com/pages/components/23929394.htm

They hybrid Biradials, looks like.

Somebody else'll have to play with them. I'm doin' PT waveguides.... :p

Steve Schell
06-24-2005, 01:01 AM
Widget, that was an important clarification. By "conical", I refer to any horn with straight walls rather than curved. A conical horn can be axisymmetric (round), square, rectangular or some other shape.

So far my experimental conical horns have been rectangular... and large. Because of the lack of low frequency loading that curved throat horns achieve, a conical horn must be quite long to achieve decent loading on the low end. Usually, conicals are a case of "measures bad, sounds good". Due to the lack of l.f. loading and broad dispersion of the highs, an on-axis response curve will typically look like Humpty Dumpty. What is not told in the measurement is the wide open clarity of sound of these horns. If one can employ some EQ to flatten the response, and can tolerate the low Spouse Acceptance Factor of really large (say 24" by 32" by 36" long for 300Hz. cutoff) horns, I think it is hard to do better.

A.J. May, who worked in loudspeaker development for decades at RCA, built many experimental conical horns about 50 years ago. He was enthusiastic about their broad, even and controllable dispersion vs. frequency. RCA never produced any conicals though, because they were too large for a given cutoff frequency.

Zilch, I agree; a conical horn will measure close to the plane wave tube response for a given driver both on and off axis, down to the horn's cutoff.

Ian Mackenzie
06-24-2005, 02:44 AM
Steve,

I was reading the paper on the 2344 horn a while ago and in it was discussed the pros and cons of various horns and geometry and in some ways the 2344 is hyprid using differaction and a certain mathematical expression for the curve.

Have you ever considered a conical/ differaction hyprid horn?

Ian

whgeiger
06-24-2005, 03:47 AM
WW,

Comments follow your text.


"When using a horn as a test jig, this is not happening; e.g., horn artifacts, at the bottom end, are manifesting themselves as distortion products due to the driver being operated below the horn’s effective pass band, which begins at least one to two octaves above horn [fc]."
I thought we discussed this already. The point is, those artifacts will affect all of these drivers in the same manner.
Sometimes the only way to get a point across is through repetition where the issue is recast in different words. Will try one more time:

Since our purpose wasn't to determine the absolute value for each driver but rather the relative performance between them
1) If the ‘what’ to be discovered and measured is hidden or suppressed under horn artifacts, then the ‘what’ remains un-observed (masked) or at least misrepresented.
2) Using either test jig (horn or PWT), the measurements are relative because
a) the unit used is dB (which is a ratio), and
b) it is cast with respect to the parameters frequency and driver.
So, in either case, the data set for each driver contains only “relative” measurements not “absolute” ones.

I think you are going over board.
That is your opinion, so be it.

Of course if you would like to make us a PWT, I'll be happy to use it in future tests. It would be nice to have one for 1", 1.5", and 2" drivers.
Cost more to ship a completed unit than to simply perform a local build. As the procedure for building them is sufficiently ‘Gerberized’, the DIY route would be the most cost effective approach to acquisition. For most, if not all, JBL compression drivers, a PWT power response sweep is published. Some are also provided in the referenced articles [1] & [2] and JBL authored technical notes.

BTW: your link didn't work... I did try to check it out.
A complementary copy of the AES standard [1] may be obtained at the following (AES revised) URL: http://www.aes.org/publications/standards/courtesy.cfm?ID=1
If you want a copy of the companion article [2], will be more than happy to e-mail it to you.

Regards,

WHG

Ian Mackenzie
06-24-2005, 04:29 AM
"When using a horn as a test jig, this is not happening; e.g., horn artifacts, at the bottom end, are manifesting themselves as distortion products due to the driver being operated below the horn’s effective pass band, which begins at least one to two octaves above horn [fc]."

I thought we discussed this already. The point is, those artifacts will affect all of these drivers in the same manner. Since our purpose wasn't to determine the absolute value for each driver but rather the relative performance between them, I think you are going over board. Of course if you would like to make us a PWT, I'll be happy to use it in future tests. It would be nice to have one for 1", 1.5", and 2" drivers.

Widget

BTW: your link didn't work... I did try to check it out.


Excellent work Zilch and The Widget,

I agree and I think it makes more productive discussion to look at this from a more practical perspective. Why would you attempt to use the horn all the way down that far anyway unless the woofer didn't have the legs? Besides the artifacts if there are any would be normally be attenuated by the high pass crossover filter..that's common sense. In anycase we can't do anything about the garbage down there so its a dead issue imho.

Of more interest as illustrated by these nice curves is the behavioural relationships b/n the various horns and drivers and their interface with real world acoustics. I would like to see some subjective appraisals at some stage, altough given the reasonable cost of these horns no doubt we can find this out for ourselves!

Ian

Steve Schell
06-24-2005, 10:11 AM
Hi Ian,

You asked "Have you ever considered a conical/ differaction hyprid horn?"

Not really. My understanding of diffraction horns and how they operate is far from complete, but I've never cared for their sound. I once bought a pair of the big JBL Biradials, and couldn't leave them in the system for more than a day or two. I have always regarded as suspect horns that have large and/or sudden changes in cross sectional shape or flare rate; they strike me as sounding confused and harsh somehow.

You may be familiar with the work of Dr. Earl Geddes. His theory is that Higher Order Modes (HOM) are very problematic. He regards HOMs as any wavefront that bounces off the horn walls and creates a delayed wave launch, much like edge diffraction on a flat baffle. He feels that these closely timed reflections confuse the sound and disrupt imaging; this all makes sense to me. In his horns, or "waveguides" as he calls them, he introduces a bit of curvature in the initial throat section to establish a spherical wavefront. The waveguide is basically close to a conical horn, with a large radius applied to the mouth to control reflections.

You can read an explanation of his theories here:

http://www.gedlee.com/downloads/Cum%20laude.pdf

J.M. LeCleach has also attacked this problem and the flare profile he has developed seeks to create a pure spherical wave launch. I don't understand the math behind his flare, but the mouth shape indicates he is attempting to control mouth reflections. His horn can be seen here, near the bottom of the page:

http://www.arduman.com/aa/Sayfalar/lecleach/lecleach.htm

Discouraging HOMs does sound to me like a great way to make a horn. The relative lack of HOMs in even rudimentary conical horns likely contributes to their clarity of sound.

While I was out surfing for links, I also ran across this golden post from Tom Danley. Whenever he is talking I try to be listening...

http://www.audioasylum.com/forums/hug/messages/85136.html

Zilch
07-06-2005, 06:45 PM
2435HPL's are back from JBL - "Cleaned gaps and added ferro-fluid." Passed final test. We'll see if they pass the Zilchster test, now. ;)

speakerdave
07-06-2005, 08:31 PM
I and my 2435's are waiting patiently for the result. Maybe it would be worthwhile for me to send mine to summer camp at Northridge.

David

Mr. Widget
07-06-2005, 11:45 PM
WW,

Comments follow your tex....

I guess I missed these comments.

Bill,

I must say that I agree with every one of your points. That said, I am reluctant to build a PWT since any tube I made would always yield results that were at least partly clouded by the question of whether or not I got the foam or fiberglass damping load properly tapered and therefore the results would still be only relative and not truly absolute. I agree that it would be closer to absolute than the use of my 500Hz horn... but the horn is here and ready to go... the PWT isn't. I may venture down that path at some point and make one for kicks. Unfortunately there are only so many audio hours in a day.:(

Ideally we will be able to get Zilch's drivers back over here to do a before and after measurement so that we can see exactly what may have been "improved" by the cleaning and reapplying of the ferro fluid. Zilch's subjective results will also be interesting.

Referring to questions about the validity of measurements made on the Ring Radiator Thread. I agree with those that said or implied that our onboard measuring devices (ears) are the ultimate judge of quality. That said I found the measured response that we posted are for the most part a validation of JBL's claims and not a contradiction. I guess there is interpretation even in objective measurements. As for which devices are superior as was pointed out by some, it primarily depends on your intended application and also to a some degree personal preferences.

As for whether or not one device measures better than another is obviously not entirely objective either. The curves that looked best to me were not the curves that looked best to Zilch. We approach the design problem differently and have different goals and therefore come to different conclusions while looking at the same objective data. There rarely is one right answer, though it is easy to forget that.


My understanding of diffraction horns and how they operate is far from complete, but I've never cared for their sound. I once bought a pair of the big JBL Biradials, and couldn't leave them in the system for more than a day or two...

I must say that based on my own experiences (both objectively and subjectively) I agree with the notion that there is a problem with sudden changes in cross sectional flare rate. In my limited experience with horns that feature an abrupt change in flare rate like the Biradial 2344 and H9800 I agree that there seem to be qualities in their reproduction of music that I subjectively find problematic. On the other hand the 2397 diffraction horn I find reasonably pleasing and also a fairly good imaging horn in a room with adequate acoustical controls. (The very wide dispersion can be problematic in live rooms.) Objectively this diffraction horn has a series of notch cancellations most likely caused by the parallel surfaces. Fortunately it is much harder to notice a notch than a peak so subjectively the horn sounds reasonably smooth. Other horns that may measure "smoother" may have slight peaks that can be objectionable. This again is where the "ultimate" test must be done by ear and is obviously also a matter of personal preference.

Widget

Zilch
07-07-2005, 11:24 PM
They sound fine. They have the flatness Mr. Widget likes, but they don't have the HF extension of 2431's. The two units are different at the high end. I don't pretend to hear any difference between Al and Be.

I conclude JBL doesn't spec 'em up there. We'll run again on CLIO to see if they are really any different from before they went in for service. A 2430H is on the way from tomp787 to complete the 243x picture. :)

#5 (top) and #6, both on PT-F waveguides, biased "AM" crossovers:

Mr. Widget
07-18-2005, 10:40 PM
Here are plots of Zilch's 2435s after being refurbished at Northridge. The red and blue plots are of the two drivers before they were sent back to JBL. The green plot is of one of them after the servicing. When we saw the two drivers performing so differently we suspected that they were out of spec. They were also suspect since they had been an eBay purchase.

Mr. Widget
07-18-2005, 10:44 PM
Here we see both of the refurbished 2435s are now nicely matched. We can also compare them to a pair of nicely matched 2431s on the same 100° by 100° PT-F wave guides. The 2435s appear to be slightly smoother in response and also about 3dB more sensitive.

Mr. Widget
07-18-2005, 10:48 PM
Forum member tomp787 was kind enough to lend us one of his 2430 drivers. Here we see it compared to a 2431. The 2430 has a different diaphragm giving it a lower FS and a bit less UHF extension. We can see the effects on the HF extension, but on this horn the lower frequency response is completely dictated by the horn cut off.

Mr. Widget
07-18-2005, 10:53 PM
Here is the 2430 on the PT-F and PT-H 100° by 100° horns and also on the PT-F 60° by 40° horn.

edgewound
07-18-2005, 10:57 PM
Here we see both of the refurbished 2435s are now nicely matched. We can also compare them to a pair of nicely matched 2431s on the same 100° by 100° PT-F wave guides. The 2435s appear to be slightly smoother in response and also about 3dB more sensitive.

Wow....3dB is huge!!! check out that knee at about 18khz? to maybe give the 2431 an impression of better UHF response...which one sounds better to you? have you done critical listening? female vocals? violin? sax? reed breath sounds?

Edgewound

Mr. Widget
07-18-2005, 11:04 PM
Here we compared the 2435 with the 435Be, the 2430 and 2431 drivers all on the H9800 horn. The response of the 2435 and the 435Be were essentially identical. The effects of the larger back cap and lack of ferro fluid of the 435Be was not noticeable in the frequency response measurement. It is quite possible that a subjective listening test would show a difference, but from strictly a frequency response measurement, they do appear very similar.

This series of measurements has shown us that there are potential hazards in buying used and untested merchandise, luckily JBL was able to come to the rescue. It also shows us a nice comparison of almost the full line of JBL's current crop of 1.5" exit 3" diaphragm drivers.

Widget

Mr. Widget
07-18-2005, 11:11 PM
check out that knee at about 18khz? to maybe give the 2431 an impression of better UHF response...

That spike at 18KHz is the result of the mass break point. All compression drivers exhibit that type of curve to some extent. Some listeners complain about the distortion or hard edge that is heard when a driver is run out to the resonant peak caused by it's mass break point others do not seem to be affected by it. If it is high enough in frequency it is typically less of a problem.



...which one sounds better to you? have you done critical listening? female vocals? violin? sax? reed breath sounds?

With the exception of the 435Be I have not listened to any of these drivers critically.

Widget

B&KMan
07-19-2005, 06:52 AM
Hi ,

I read with a very great interest the series of tests which you expose
here... It is an enormous work with the implementation of much of resource.

:applaud: :applaud: :applaud:

after having read and observed the different plot ones I believe
that it would be very advised for more objectively seizing the
difference which you expose the response in distortions of different
the driver. I believe that the level of distortion of the harmonics, 1,3,5, with step eloquence would expose new light of the differences of each driver...

WHAT think about it???

Jean.

Mr. Widget
07-19-2005, 09:56 AM
I believe that the level of distortion of the harmonics, 1,3,5, with step eloquence would expose new light of the differences of each driver...

WHAT think about it???

I agree that it would be useful, along with PWT measurements as has been suggested. However even this cursory look at these drivers was a fair amount of work and was only meant as a starting point. I do think that this information does shed some light on these drivers that was not available to the DIY community before we undertook the project. Anyone who would like to do some serious design work around these drivers will likely need to do additional testing.

If someone would like to continue the work and fully analyze these drivers that would be great.

Widget

Zilch
07-19-2005, 10:22 AM
Rudimentary power testing/distortion plots are provided at posts 28, 29, and 30....

B&KMan
07-19-2005, 10:22 AM
hi Mr. Widget,

to have made a very small part of this kind of work on my 4343, I then without hesitate to recognize the amount of work and I pick you
up my hat!

:applaud: :applaud: :applaud:


My remark wanted to be an extension of the questioning more the
performance of the HP... Indeed, an evaluation in power of the harmonics could undoubtedly expose good difference between the HP... in the same way the evaluation of the differences at the time of the change of the diaphragm or magnet by the harmonics would also more clearly expose the nature of the differences... and once again, I hello this large work and this generosity to divide this expensive and precious information.


Jean.



(currently I am seeing whether I then to make an evaluation of the
harmonics with my analyzers. The problem is that B&K has to develop a specific analyzer for that but costs only $ 50 000)
If I then to make this study, it would please to me to contribute to this analysis... I would send a p.m. in the positive case).

:cheers:

B&KMan
07-19-2005, 10:34 AM
Rudimentary power testing/distortion plots are provided at posts 28, 29, and 30....

hello Zilch,

Oups!!! I believed that modifications had been made meanwhile on the HP and
that a new harmonics evaluation would have exposed these facts...

all my excuses...

In addition, It seems to to me odd that at the beginning of the curves; the harmonics is stronger than the fundamental ones...

is this normal really???

Jean.

Mr. Widget
07-19-2005, 10:36 AM
The problem is that B&K has to develop a specific analyzer for that but costs only $ 50 000)


Clio is under $2K and is probably better suited to measuring loudspeakers anyway. Join the digital revolution!

http://www.e-speakers.com/products/cliowin.html

Widget

Zilch
07-19-2005, 11:21 AM
I believed that modifications had been made meanwhile on the HP and that a new harmonics evaluation would have exposed these facts....Well, you're right. The 2435HPL's were rehabbed by JBL.

I'll consult with Mr. Widget on the potential of LIMITED additional testing. :p

[I and others would likely appreciate knowing how 2430 distortion compares with the other drivers in the family, as well....]

johnaec
07-19-2005, 12:49 PM
In addition, It seems to to me odd that at the beginning of the curves; the harmonics is stronger than the fundamental ones...The distortion levels were raised 30db in those plots for clarity.

John

B&KMan
07-19-2005, 08:52 PM
hello again,

In front of the enormous energy and effort which you provided to
clarify this forum...

I allow myself to give here my contribution to two pennies...

The evaluation of the HP must pass by the analyses of the harmonics. all the world gets along on that... The majority of the defects to the performance evaluation pass by an
analysis of the harmonics not of 2 or 3, who does not show anything, but of harmonics 5 to 11.

In effect, according to my documentation, the defects are clearly distinguishable in the distant secondary harmonics. ex: rub sound pushes the 7 and 9 harmonic of more than 20 dB: that passes from a normal driver of -70 to less -50 dB what becomes audible like distortion...

thus with all the fan of CLio and others, please do not hesitate to request your computers with the max power to perceive that...

thanks so much in advance... :D


:cheers:


Jean.

B&KMan
07-19-2005, 09:45 PM
Well, you're right. The 2435HPL's were rehabbed by JBL.

I'll consult with Mr. Widget on the potential of LIMITED additional testing. :p

[I and others would likely appreciate knowing how 2430 distortion compares with the other drivers in the family, as well....]


:bouncy: YES :bouncy: YES :bouncy: YES


:applaud: PLEASE :applaud: PLEASE :applaud: PLEASE :applaud:



:D

Tom Loizeaux
07-23-2005, 11:22 AM
I would like to ask a question about horn / driver compatability:
Will a compression driver (JBL 2426H) perform correctly when mounted to an expoential fiberglass horn? The horn is similar to the Community Sound 800Hz horns with the extending "lips", so there's a soft roll at the edge of the flares. Also, I'm using this combination for high frequency only (3.5K and up). Will these horns let the 2426 drivers deliver this top end properly?
(These are for PA use, not audiophile listening)

Thanks,

Tom

Mr. Widget
07-23-2005, 11:33 AM
There is certainly no harm in sticking it on the horn and giving it a whirl. The 2426 has essentially the same requirements as the LE85/2420 and most other 1" exit drivers. It should perform as well on that horn as any driver can.

Since it is an exponential horn it will have decent HF performance on axis, but will likely fall off at higher frequencies off axis.

Widget

Zilch
07-25-2005, 09:49 AM
Thus far, I can attest that Mr. Widget has reliably detected buzzing/rubbing drivers without measuring 5+ order harmonics.

[Even with his fingers stuck in his ears.... :p ]

Guido
02-14-2006, 03:32 AM
Here is a plot of Zilch's "better" 2435HPL. We are not sure what the specs are for distortion, but this unit has significantly more third harmonic distortion that the 435Be.

Widget and Zilch,

Was this measurement redone with the refurbished 2435? I was looking for this info but couldn't find it.

Mr. Widget
02-14-2006, 09:22 AM
Widget and Zilch,

Was this measurement redone with the refurbished 2435? I was looking for this info but couldn't find it.We did run measurements using the 2345s after they came back from rehab.... I have no idea which thread they are buried in. Zilch may have kept copies, I have not.


Widget

Zilch
02-14-2006, 09:39 AM
We're pretty conscientious about keeping related material in the same thread here.

See post #68 et.seq. :thmbsup:

Mr. Widget
02-14-2006, 09:45 AM
We're pretty conscientious about keeping related material in the same thread here.

See post #68 et.seq. :thmbsup:Yeah, sorta, sometimes... I was too lazy to start digging.

Thanks Zilch.


Widget

Guido
02-14-2006, 11:03 AM
We're pretty conscientious about keeping related material in the same thread here.

See post #68 et.seq. :thmbsup:

OK, sometimes I'm blind but not so blind. I mean distortion measurements. The 2435HPL first had quiet high distortion. Was it measured again after refurbishing?

Zilch
02-14-2006, 11:20 AM
No, sorry.

I'll put it on the list for CLIO testing here.... :thmbsup:

Did you read the Geddes article on distortion in the latest AES Journal?

Guido
03-07-2006, 03:51 PM
Did you read the Geddes article on distortion in the latest AES Journal?

I overread this. Do you have it? You still have my mail addy, yes? ;)

Steve Gonzales
04-13-2006, 05:39 PM
An older thread with a weath of good information!!! I hope some of the newer members will take a look at this thread. This definately sheds light on what an engineer must figure out before going into production. For the members that are already up to speed on this stuff, I can understand a bit better now, how a novice might look like when he stuffs a horn/driver into an unintended enclosure. We're all after the same thing, it's just a steeper learning curve. Armed with this quality information, not so steep now.

mbask
03-06-2007, 02:39 PM
Oh...good they're gone

Too Tall clist
04-22-2007, 10:09 AM
Here is a plot of Zilch's "better" 2435HPL. We are not sure what the specs are for distortion, but this unit has significantly more third harmonic distortion than the 435Be.


Hi,
I just started working on a passive xover with a 2435HPL.
I can’t give you any useful measurements right now because the 1.5” throat driver was mounted on a 2” throat horn. So right now someone is looking for some 1.5” throat horns that will fit in the cabinet.

I did have some question pertaining to the driver itself.
I have heard some outrageous quotes for what the driver will sell for.
If you go here you will see a retail replacement cost of the diaphragm (I presume) of $756.00

http://www.jblproservice.com/pdf/Transducers%20Parts%20List/Transducer%20Parts%20List.pdf

All this because of the use of Beryllium.

Note on the same spreadsheet the 2431 diaphragm retails at $138.00.

I have seen several 2435HPL on ebay for around $240 each.
About 1/3rd the cost of its diaphragm?

So I wanted to know if there were after-market diaphragms made from something less expensive like aluminum? And that is why they were going so cheap on ebay?

Considering the cost of the diaphragm it would seem fool hardy to use these for anything less lucrative then corporate gigs or something else that pays as well.
Frying one in a 150 seat night club in the middle of a 80s rock tune might cause you to be clinically depressed.
The Talking Heads are important, but not THAT important.

I decided to attach a picture (If I can figure out how…). Note again it is mounted on a 2” throat Selenium HMA4750-SLF 90x40 horn.
No throat adapter was used, which is why the high frequencies above 6.7kHz are obliterated.

The frequency response below that should be valid.

For measurement background-
Measurement program is Praxis with a Praxis mic.
The horn was dropped into a wastebasket to point it straight up and a mic 1 meter above the mouth pointing down. So there was no baffle, just the horn itself.
The IR was gated at about 10ms to remove the ceiling bounce. The window was about 7ms long (I think).

If you look at the top of the plot it says 9.03dB offset.
Praxis measures referenced to 1-volt. To find 1-watt 2.83V into 8ohm you add 9.03dB
And this is an 8-ohm nominal driver with everything in its useful range at 6ohms (except for resonant peaks.)

So the frequency SPL is correct for the horn used.

If I figure it out I will post the z plot too.

I hope someone can help me out with the after-market diaphragm question.
Thanks.

Zilch
04-22-2007, 10:28 AM
http://audioheritage.org/vbulletin/showthread.php?t=14357

Robh3606
04-22-2007, 10:33 AM
So I wanted to know if there were after-market diaphragms made from something less expensive like aluminum? And that is why they were going so cheap on ebay?


No aftermarkets are available that I know. The drivers on Ebay are the real deal. Some need the gaps cleaned but other than that they are a real bargain. You can run a 2431 aluminum in a 2435 core and visa versa. They are the same driver asside from the diaphram material.

Rob:)

Mr. Widget
04-22-2007, 11:24 AM
No aftermarkets are available that I know... You can run a 2431 aluminum in a 2435 core and visa versa. They are the same driver asside from the diaphram material.Yep... but there is a reason for that expensive beryllium. Performance.

I have no idea if you will be able to appreciate the difference in a club setting, but there is no comparison between them in a studio monitor or high end home system.

You might want to buy a pair of the $138 aluminum diaphragms and see if they satisfy your needs.


Widget

Too Tall clist
04-22-2007, 12:02 PM
Yep... but there is a reason for that expensive beryllium. Performance.

I have no idea if you will be able to appreciate the difference in a club setting, but there is no comparison between them in a studio monitor or high end home system.

You might want to buy a pair of the $138 aluminum diaphragms and see if they satisfy your needs.


Widget

Hi and Thanks.

These aren’t for me. I’m just designing the xover.
I do appreciate the performance issues, but I don’t want my customer to get in over his head either.

For example if the 2435 drivers he has have aluminum diaphragms in them if he destroys one he might be able to afford the replacement.
If they are the expensive spread I want him to know what it’s going to cost him BEFORE I design a xover for him. I don’t know if my design will work with both diaphragms till it’s done.

Also at the price point on ebay I would not be surprised if they are 2431 diaphragms.

What is the best way to determine which diaphragm is in there?

So, have we decided how low a 4th order xover is safe for these?

edgewound
04-22-2007, 12:22 PM
I got my (4) 2435's from a guy on eBay as well. I haven't looked at the most recent auctions, but he is a guy in Hesperia, CA.

He delivered mine to my shop. Very nice guy. He said they came from Vertec systems from a huge nightclub operation that went out of business.

I havent had the occasion to replace any diaphragms yet on 2431 or 2435 but I have opened mine to look at the dia's, and yes, they are Be.

I'm not so sure they are a drop-in interchange without modifying the mounting ring.

It would make more sense to just buy 2431 driver's outright, if the cost is an issue....which for most people it would be.

The Ferrofluid has dual purposes: (1) wick away heat from the voice coil to the top-plate (2) Dampen the moving mass for less distortion....but at the expense of minimal sensitivity loss.

edgewound
04-22-2007, 12:27 PM
So, have we decided how low a 4th order xover is safe for these?



Seems to me that passive for 2435 is too high risk in a live situation. I'd think that active digital with brick wall filters and comp/limiting would be the best bet.

Too Tall clist
04-22-2007, 01:43 PM
Seems to me that passive for 2435 is too high risk in a live situation. I'd think that active digital with brick wall filters and comp/limiting would be the best bet.

I don't see the risk.
If the design is correct the passive filer should work as well as the digital. If you are going to push the speaker to the edge the DBX 160 is in the first rack 2 spaces down below the Varicurve.

As for your brick wall filter if I move the xover up just a little bit there is little difference.

One thing is for sure. On the financial front, if you can afford those drivers you should be able to afford a Lake DSP for a system controller.

And I still would like to know what is recommended for a 4th order high pass, because despite the fact that a DSP is better or not these are going in 2-way passive with a 12" cone because that is what he owns.
Thanks

Zilch
04-22-2007, 02:33 PM
Look to the JBL products using 2431 to choose a waveguide, AE series, typically. Crossover guidance is there for each.

Other options, 2381, 235x horns.

Can't do the crossover without knowing and measuring on the horn/waveguide to be used....

Oldmics
04-22-2007, 02:55 PM
Curtis-Buddy

Welcome to the Lansing Heritage Site !!!:applaud: :applaud: :applaud:

For those of you who may not know,TooTall is a fluid Praxis analysis user.

His level headed,well thought out contributions on "Pro Sound News Live Audio Board" are one of the reasons that I still attend that site.

I heartly welcome Curtis here and hope that the rest of our members also do the same.

There are some really good minds here Curtis that are exploring a different realm of the audio experience.Best of all NO debates about the latest fad in pro gear (well sometimes).

How about no Nexo v/s "L" Acoustics debates (or whatever) that just turn me off over at the L.A.B.,you get the idea.

I am sure that Curtis will prove to be a valuable assett here.

Welcome aboard :bouncy:

Oldmics (Funzilo)

Sooner Fan
04-22-2007, 03:14 PM
I don't see the risk.
If the design is correct the passive filer should work as well as the digital. If you are going to push the speaker to the edge the DBX 160 is in the first rack 2 spaces down below the Varicurve.

As for your brick wall filter if I move the xover up just a little bit there is little difference.

One thing is for sure. On the financial front, if you can afford those drivers you should be able to afford a Lake DSP for a system controller.

And I still would like to know what is recommended for a 4th order high pass, because despite the fact that a DSP is better or not these are going in 2-way passive with a 12" cone because that is what he owns.
Thanks

When you guys figure out a network for a great 2 way using the 2435hpl I hope you will post it. Ive got 4 laying around here I would like to do something with.

Go Sooners

edgewound
04-22-2007, 04:10 PM
I don't see the risk.
If the design is correct the passive filer should work as well as the digital. If you are going to push the speaker to the edge the DBX 160 is in the first rack 2 spaces down below the Varicurve.

As for your brick wall filter if I move the xover up just a little bit there is little difference.

One thing is for sure. On the financial front, if you can afford those drivers you should be able to afford a Lake DSP for a system controller.

And I still would like to know what is recommended for a 4th order high pass, because despite the fact that a DSP is better or not these are going in 2-way passive with a 12" cone because that is what he owns.
Thanks

Maybe it'll help you come up with a passive crossover based on the factory specs of the 2435 contained here:
http://www.jblpro.com/vertec1/vertec_manual/Vertec%20Chap%204A.pdf

I think maybe the filter gurus here might be gun-shy to suggest a design based on the possible liability of it being used singley for a live rig.

The 2435HPL was designed specifically for the VerTec line array, and uses (3) units per system. The similar 435Be is used in JBL's Project Array Series for HT/ hifi use.

Also notice that the power handling relies somewhat on the heat dissipating utility of the aluminum VerTec wave guide.

The crossover freq you choose will also depend on what 12" you're going to use...what's it's Freq resp, Sensitivity, power handling, etc.?...Vocal monitor? Small mains?

Making this driver work too hard for too long is just asking for a very expensive repair....but...whatever....it's his money.

BTW....Welcome...Oldmics gives you a great reference and that's good enough for me.:) ;)

Earl K
04-23-2007, 06:42 AM
What is the best way to determine which diaphragm is in there?

- Zilch included a very useful link in his post . Within that ( "linked-to" ) thread , RobH has a pic of what a Be diaphragm looks like . The implied directive is to open up the driver and take a look for a very "dark" diaphragm .


So, have we decided how low a 4th order xover is safe for these?

- IMO: For SR work ; ( a 2435H in a stage monitor with a 12", & on a small horn ) , I would use a ( 24-db ) point in the 1500 hz range .
- FWIW, JBL does use the 2431 in a bunch of SR products that have Xover points ranging from 1100 hz up to 2K ( all horn dependant ) . 1200 hz being about the most common published point.

- Fair Warning JBLs' published points of 1200 hz could well be a bit misleading until a person does a complete diagnostic workup of the various schematics for these products and looks at the voltage drives. From the published FR graphs that I've seen ( by Zilch ) , all of JBLs' applicable horns ( waveguides really ) seem to have lost loading in the 1500 hz region and are already down about 3 db by that point .
- JBLs' family of small format waveguides have a lot of planar surfaces built into them which can be great for obtaining solid HF coverage without having to fall back on implementing diffraction corners . IMO, the downside is all these flat planar surfaces come from the conical family & that family of horns typically comes with compromised lowend loading ( when compared to pure exponentials ) .
- Frankly , ( IMHO ) DDS does a better job in the "small horn catergory" because they have included more exponential wall curve ( for LF loading ) within their designs of small constant coverage horns.

- & If you have all the necessary test gear ( which you seem to ) you can ;
(i) choose a horn that fits the stage monitor size requirements , and then
(ii) using a sweepable 24 db LR type crossover
(iii) run enough pink noise into the horn/driver combo to get @ 10% measurable distortion product in that 1 octave region ( 1/2 octave either side ) of the chosen crossover point . ( Perhaps 15% plus is allowable & more realistic in SR work ??? I don't really know ) . Either way, tolerable distortion specs will need to be a personal choice made by you & the end user .

:)

Too Tall clist
04-23-2007, 07:08 AM
Maybe it'll help you come up with a passive crossover based on the factory specs of the 2435 contained here:
http://www.jblpro.com/vertec1/vertec_manual/Vertec%20Chap%204A.pdf


Thanks, that is a start.
Do you have the address for the entire manual instead of those couple pages?

That is about powering them and I am looking for the tuning. I looked through the JBLPro links and there is one for tuning (Such as the HLA series), but not the Vertec. I found the Vertec corner of the world, but not what I need so far.

They may not show specifics since the 24235HPL is not sold as “components”.
I am most likely screwed since anything they have will be based on using three on their wave guide. This will alter the low frequency extension and how low I can operate them safely on another horn and one at a time.

Well I suppose I can get some clues from where the harmonic distortion increases…



I think maybe the filter gurus here might be gun-shy to suggest a design based on the possible liability of it being used singley for a live rig.

The 2435HPL was designed specifically for the VerTec line array, and uses (3) units per system. The similar 435Be is used in JBL's Project Array Series for HT/ hifi use.

Also notice that the power handling relies somewhat on the heat dissipating utility of the aluminum VerTec wave guide.


Hmmm, I had not considered the heat issue.
OTOH the whole system in a Vertec is balanced to get everything they can out of it.
I will only have one 2435, but it only has to keep up with one front loaded 12” instead of two 15”.



The crossover freq you choose will also depend on what 12" you're going to use...what's it's Freq resp, Sensitivity, power handling, etc.?...Vocal monitor? Small mains?


This will be a small FOH box.
For any of these I first look at how low I can go with the horn/compression driver. The woofer has to reach for frequency or we need another 12”. You can’t cheat the horn much.
I can go to the high-pass filter on the woofer to “stretch” its bandwidth without worrying I will fry it. I have started out with 4th order low pass and ended up with a single inductor to make it work.

As for sensitivity the horn has to be on a pad to match. The sensitivity of the 12” will be controlled by how low you need it to go and how big the box is.
Did you design for baffle step or not? That is another 6dB gone.



Making this driver work too hard for too long is just asking for a very expensive repair....but...whatever....it's his money.


I am going to try to talk him out of it.



BTW....Welcome...Oldmics gives you a great reference and that's good enough for me.

Thanks,
Much appreciated.
:)

Too Tall clist
04-23-2007, 07:12 AM
Curtis-Buddy

Welcome to the Lansing Heritage Site !!!:applaud: :applaud: :applaud:

For those of you who may not know,TooTall is a fluid Praxis analysis user.

His level headed,well thought out contributions on "Pro Sound News Live Audio Board" are one of the reasons that I still attend that site.

I heartly welcome Curtis here and hope that the rest of our members also do the same.

There are some really good minds here Curtis that are exploring a different realm of the audio experience.Best of all NO debates about the latest fad in pro gear (well sometimes).

How about no Nexo v/s "L" Acoustics debates (or whatever) that just turn me off over at the L.A.B.,you get the idea.

I am sure that Curtis will prove to be a valuable assett here.

Welcome aboard :bouncy:

Oldmics (Funzilo)

Thanks much.
Too Tall

johnaec
04-23-2007, 07:17 AM
Id suggest looking over Zilch's many test curves of the 2435H on various horns. Here's an example: http://audioheritage.org/vbulletin/showpost.php?p=147389&postcount=23 , (go to the complete thread Zilch posted earlier for more curves). Zilch has posted much more than this, in other threads. If you do an advanced search for 2435H posted by Zilch, you'll find an amazing amount of info posted. Whether it will translate into useful info for your needs will probably depend on what horn you end up using.

Joh

Too Tall clist
04-23-2007, 07:21 AM
When you guys figure out a network for a great 2 way using the 2435hpl I hope you will post it. Ive got 4 laying around here I would like to do something with.

Go Sooners

Hi,
Passive networks don't play well with strangers. I just tried using a different 12" woofer in a design with the hope that we could leave the high pass on the horn driver alone and cut design time in half (somehow).
No luck.
The design came from modeling with LspCAD. It intertwines things so much at the xover point that putting in a different 12” means most things have to change enough to make the design useless for anything else.

You do have a MUCH better chance with active analog (no impedance issues) and even better with a DSP xover.

Sorry.
Too Tall

Earl K
04-23-2007, 07:35 AM
Hi Too Tall,


I'd suggest that you start reading here, at this post in Zilches' lengthy Q & A tome (http://audioheritage.csdco.com/vbulletin/showthread.php?p=54744#post54744). There you will find JBLs' official engineering specs for the 2430,1 & 2435 drivers ( these are on this site, courtesy of Giskard ) .

EDIT :
- I just noticed that your project is a FOH build / Oops / so, ignore those references of mine about stage monitors .

- Also, somewhere on this site Zilch has posted pdfs of JBLs' network schematics, for the "AM Series" of FOH boxes. They typically use a 2431h on a mid-size waveguide, along with a 2206H 12" woofer . These schematics can give the network designer a few ideas ; including applicable HF horn compensation, as well as some insight into how JBL is implementing "narrow-band LCR induced notches" for both the horn driver and woofer circuits . JBLs' network designer , obviously has decided the end result is worth the hassle of adding all the extra components necessary for LCR traps .

- Here are the "AM" schematics. They are found within this post from Zilch. (http://audioheritage.csdco.com/vbulletin/showpost.php?p=50877&postcount=363)
:)

4313B
04-23-2007, 08:42 AM
Whether it will translate into useful info for your needs will probably depend on what horn you end up using.Unfortunately he is better off doing his own measurements for his own purposes. Please be aware that many of us have the ability to post graphs day and night but, as JBL has also stated (they used to look over these forums fairly regularly), doing so is fairly pointless.

Now, when people finish projects like John has done and post a few graphs along with their project, that's a somewhat different story and can actually be quite interesting. If others decide not to post any graphs for whatever reason that certainly doesn't detract from the experience.

Also note that JBL isn't entirely consistent in their measurements either depending on who takes the measurements and for what purpose. Compression driver plots are somewhat consistent on the plane wave tube since there is only one test station and it remains a constant for a long period of time.

Robh3606
04-23-2007, 10:11 AM
Hello Too Tall

Giskards right you really need to do your own measurements with the driver mounted on horn and baffle to see what type of compensation you are going to need in the end. I run mine active using 24db slopes and then use a comp circuit to help flatten the response. I can't imagine them being any less rugged than any other JBL driver as long as they are properly heat sinked. They sure do sound nice.

Rob:)

edgewound
04-23-2007, 10:48 AM
Look here for more detailed specs:

http://www.audioheritage.org/vbulletin/showthread.php?t=14369&highlight=435Be

Too Tall clist
04-24-2007, 08:01 AM
2435HPL's are back from JBL - "Cleaned gaps and added ferro-fluid." Passed final test. We'll see if they pass the Zilchster test, now. ;)

Hi Zilch,
What did JBL charge for the service?

Earl K
04-24-2007, 08:23 AM
Hi Too Tall

- In response to one of your original questions / JBL has hipassed variants of these drivers in the 700 hz region . The variants have larger back-caps and sometimes have aquaplased diaphragms .

- After scanning your Praxis graphs / JBLs' practice ( when using their midsized, HiFi BiRadials ) fairly well conforms to the impedance swings ( acoustic & electrical ) that I see happening ( with your 2435 driver on that Selenium horn ) .

- "Acoustically", an extra 45° of phase rotation from the horns' "baseline" acoustical phase change ( looking to be around 70° ) / gives 115° which is right in the 700 hz region . I chose 45° of acoustic phase rotation because electrically, 45° should be representing a 3 db down point in power output .
- I'm really just assuming this is the onset of acoustic unloading . Distortion measurements would help support that contention .


:)

Too Tall clist
04-24-2007, 08:50 AM
Hello Too Tall

Giskards right you really need to do your own measurements with the driver mounted on horn and baffle to see what type of compensation you are going to need in the end.
snip-

Rob:)

That is how I have done every crossover design for the past 9 years.
In Jan 1998 I bought a DOS MLS program called LAUD (Liberty Audio Suite)
ALong with that in the package I bought LspCAD for modeling box and xover.
I bought Praxis when it came out and became a beta tester
I am also a beta tester for LspCAD which is now up to Version 6.

A typical horn plus 12” woofer has these features-

4th order acoustic slope for low and high pass (Electrical transfer function adjusted to meet that criteria)

Low freq-
Baffle step compensation built into 4th order components. NO SERIES RESISTORS USED UNDER ANY CONDITION on low pass.
Zobel if necessary.

High freq
In most cases parallel resonance (LCR) circuit used to knock down 1kHz to 4kHz bandwidth to compensate for CD horn.
In many cases it also evens out other peaks related to compression driver and/or horn design (or lack there of).
In most cases if horn impedance resonance peak is near xover point a series resonance shunt is used to knock down the impedance peak(s) allowing the high pass to work properly. In the beginning I did not use this so much, but with horns its difficult to get around it.


If the person is not local they have to ship the box to me.
This person had some business a couple hours from me so it worked out.

Here is what one looks like when its done.
Low pass on the right and high pass on the left. The notch filter for the horn lives on the low pass board.
For scale the boards are each 6" by 12"
This is for a 15"/1" coax

Cheers
Too Tall

mini
07-07-2008, 07:30 AM
His theory is that Higher Order Modes (HOM) are very problematic. He regards HOMs as any wavefront that bounces off the horn walls and creates a delayed wave launch, much like edge diffraction on a flat baffle.

Hi,

An old thread found while looking for PT waveguides. Many of You might not exactly imagine what the HOM hype is all about.

Dr. Geddes did a real great job on horn calculations, I mean it. From that he derived a suspicion regarding Higher Order Modes, HOM for short (it is a trade mark for male underwear here in Europe, beware of copyright issues!).

His claim is that HOM has ever since degraded waveguide sound until his own special one was commercially available. The only investigation regarding audibility of HOM has not shown the effect of HOM directly. It is hold as its signature that HOM introduces undulations on the amplitude and phase response. From a certain degree of contamination as to say this is quite audible. So far so good. That we knew before already.

If HOM does not become perceptable by superstition we have to deal with the generated sound field. The only effect is linear distortion so far, namely phase and amplitude aberrations. We know how much of it is critical. Why not forget about HOM then? It's just an other source of the above mentioned linear distortion. As is diffraction at edges (enclosure, horn rim, finite horn length even with the Geddes type), interferences from driver internals, crossovers and a lot more.

Look at the graphs and You might discuss the whole total of linear distortion. Is it critical or not? With most of the more honorable systems one would find that it is not.

HOM for itsself is prone to misconception. The lowest order mode - in contradiction to the higher ones - of wave propagation in a horn is some kind of arbritary:
- with Websters horn theory the lowest order is a plane wave
- with tractrix it is a spherical wave
- with Geddes it is something else

A waveguide is virtually HOM free only when the lowest oder mode is THE mathematically exact solution of wave equation with given boudary conditions.

Geddes is right in saying that his oblate something is one that solves the wave equation exactly. But it does only with infinite horn length with that exactness - as far as I understand the whole deal. With that given even Geddes type waveguides have its hassle with HOM.
Additionally one should not forget that the driver itsself introduces HOM. It is questionable how far a waveguide reacts on that, could it attenuate that - a long way to go ... . As Geddes' waveguide has to deal with HOM anyhow, from what do we tell that Geddes' oblate something is better than prevous designs regarding - as shown above - arbitrary defined HOM?

Look at the graphs and decide from that. Considering HOM as a source of something mystique "bad" is misleading. HOM isn't to well defined and its effect on hearing delight hasn't been shown in to bright light by now.

buy

ehm: If Geddes' waveguide do measure good, they are good. But the same is true for all the others. As expenses with Geddes' solution do not explode as with some fairy tales in audio You may decide by taste first, omitting any HOMology. It seems his SUMMA is an honorable offspring of the 4430 but with a smoother response. in't it?.

Zilch
07-08-2008, 10:51 AM
Geddes admits his waveguide has HOMs, and he stuffs it with foam to attenuate them. Not HOMless.

It's almost an angels on a pin thing in context, in my view.

Here's Altec enthusiasts' favorite 902 and horns:

http://audioheritage.org/vbulletin/attachment.php?attachmentid=32409&stc=1&d=1210007988

Find me the HOMs. :blink:

http://audioheritage.org/vbulletin/showthread.php?p=208995#post208995

Robh3606
07-08-2008, 11:53 AM
You might have better luck in the time domain.

Rob:)

Mr. Widget
07-08-2008, 09:55 PM
You might have better luck in the time domain.

Rob:) :rotfl:

We all pick the gremlins we choose to battle.


Widget

mini
07-08-2008, 10:29 PM
Geddes admits his waveguide has HOMs, and he stuffs it with foam to attenuate them. Not HOMless.

It's almost an angels on a pin thing in context, in my view.

Here's Altec ...


Hi,

It's obvious that the Altecs sound field will suffer from degraded linearity, if someone is keen on using them. Whether the consumer would feel a degraded delight in hearing his music is an other question. It has a lot to do with believes, whether the perception could be trusted as being correct, true, natural - in contradiction to faulty, wrong, ehm - supernatural :D

This in mind Geddes' claims on "HOM" are a bit misleading. It's not only a question as "how many angles could rest on the pin". The problem lies :D in the method of how audio quality is evaluated.

The generated sound field should be related to human hearing. Science, statistical proof, real people, real effect. Speculations on reasons for difficulties with the reproduction are unavoidable. But they should be proven in the end. Unfortunately this is not true with HOM. As long as this is so, HOM - ill defined - should not be held against anything.

Conclusion: "HOM"-talking could degrade Your delight in hearing music via Your very stereo set. Simply by disturbing Your belief that everything is just fine. What a pitty!

Take care

ps, to bring it back to solid grounds: Geddes' waveguide is not to much more linear than EVs HP940. Even in off axis response both are quite similar. The 2352/2447 combo performs better up to 10k. But Geddes' is small, serves home audio with wide distribution, shows no directivity flip 'cause of axial symmetry ... not at least it is relatively cheap! It doesn't need that hype. The foam - measurements?