Passive CD EQ solutuions for 2365 with 2446j

[Jennifer]

I know there are plenty of systems being listened to by members here with either 2360 or 2365 CD horns with 2446j drivers, and I am about to join that crowd with my own pair. Current bottom will be done with already running GPA-Altec 515-8LF 16 inchers in large scoop type enclosures with electronic EQ. Custom electronic crossover, 4th order Linquitz Riley is sweepable. Upper power is 2A3 push pull tubes of about 15 watts, or BAT VK-60 [ way too much power ] . I have 2241g drivers that will eventually get enclosures and become the lower section for these horns.

I have carefully measured the impedance of the horn/driver system, and acoustic output outdoors facing straight up. From that I have done my own network that has a broad Q dip of about 5 sB between 450 Hz and 7KHz, centering in the 1 to 2 KHz region. Above 7K I put in a 4 dB tilt up extending all the way. Given the nature of the horn throat at 2" and the limited frequency range of the Ti diahram in the 2446j, I know it is not advisable to EQ too much in attempt to force the upper octave to be near flat, but a gentle nudge in that direction seems to be accaptable, given the comments I have looked at over the past few years. I have not yet built my network, just used modeling software to design the filters to arrive a the curve I desire. I WILL publish it here good or bad, shortly, so that we can all learn as a comminity and you guys can comment [ I need to put photos of the pages into Photobucket to get them shared here, will do very soon] . I am interested in learning what other people have done with these horn and driver to effect a CD compensation, and if anyone bothers to deal with the slight hump in the 1 to 7 K region.

Last year I found and read a JBL document that had a number of suggested schematics that had some EQ lift at the top, but I have lost the link, or if I ever had it, the .pdf. It was very long handbook or app note format, not a data sheet/support document for a specific component like a JBL passive crossover. I have re-found the cinema installers manual, but it just has theory of acoustics and how to make good sound in the audience, nothing about engineering a speaker system to do that with. If anyone recalls a handbook or contracters manual that discusses CD EQ and has schematics, I would appreciate a link... I just wasted 3 hours looking all over here and the internet for something and came up zero so far.

Please drop in with your passive EQ solutions. Also interested in EQ if you have installed Be from Truextant...which are flatter in the mid and higher up, as well as less colored. They are not in my immediate future, but farther out, yes.

Cheers
Jennifer
Here is the hand drawn plot of the impedance and the output....I had impedance in WT-2, and output in a borrowed AP System 2, so to see the data together I just made this sketch....


This would be my desired curve to dip the bulge in the upper mids, and lift the highs a little bit


This is my proposed network. Because the actual impedances are bumpy up and down, I just estimated the average over the band area if interest to run the calculations...


http://www.mh-audio.nl/spk_calc.asp This fellow has a nice website for doing calcs..It IS a good place to become familiar with if you DIY or even if you do design for a living, and need some calcs for which you don't have the specific program.

[ivica]

I know there are plenty of systems being listened to by members here with either 2360 or 2365 CD horns with 2446j drivers, and I am about to join that cround with my own pair. Current bottom will be done with already running GPA-Altec 515-8LF 16 inchers in large scoop type enclosures with electronic EQ. Custom electronic crossover, 4th order Linquitz Riley is sweepable. Upper power is 2A3 push pull tubes of about 15 watts, or BAT VK-60 [ way too much power ] . I have 2241g drivers that will eventually get enclosures and become the lower section for these horns.

I have carefully measured the impedance of the horn/driver system, and acoustic output outdoors facing straight up. From that I have done my own network that has a broad Q dip of about 5 sB between 450 Hz and 7KHz, centering in the 1 to 2 KHz region. Above 7K I put in a 4 dB tilt up extending all the way. Given the nature of the horn throat at 2" and the limited frequency range of the Ti diahram in the 2446j, I know it is not advisable to EQ too much in attempt to force the upper octave to be near flat, but a gentle nudge in that direction seems to be accaptable, given the comments I have looked at over the past few years. I have not yet built my network, just used modeling software to design the filters to arrive a the curve I desire. I WILL publish it here good or bad, shortly, so that we can all learn as a comminity and you guys can comment [ I need to put photos of the pages into Photobucket to get them shared here, will do very soon] . I am interested in learning what other people have done with these horn and driver to effect a CD compensation, and if anyone bothers to deal with the slight hump in the 1 to 7 K region.

Last year I found and read a JBL document that had a number of suggested schematics that had some EQ lift at the top, but I have lost the link, or if I ever had it, the .pdf. It was very long handbook or app note format, not a data sheet/support document for a specific component like a JBL passive crossover. I have re-found the cinema installers manual, but it just has theory of acoustics and how to make good sound in the audience, nothing about engineering a speaker system to do that with. If anyone recalls a handbook or contracters manual that discusses CD EQ and has schematics, I would appreciate a link... I just wasted 3 hours looking all over here and the internet for something and came up zero so far.

Please drop in with your passive EQ solutions. Also interested in EQ if you have installed Be from Truextant...which are flatter in the mid and higher up, as well as less colored. They are not in my immediate future, but farther out, yes.

Cheers
Jennifer
Here is the hand drawn plot of the impedance and the output....I had impedance in WT-2, and output in a borrowed AP System 2, so to see the data together I just made this sketch....


This would be my desired curve to dip the bulge in the upper mids, and lift the highs a little bit


This is my proposed network. Because the actual impedances are bumpy up and down, I just estimated the average over the band area if interest to run the calculations...


http://www.mh-audio.nl/spk_calc.asp This fellow has a nice website for doing calcs..It IS a good place to become familiar with if you DIY or even if you do design for a living, and need some calcs for which you don't have the specific program.

Hi Jennifer,

Firstly I would start from here:

http://www.audioheritage.org/vbulletin/showthread.php?18913-Altec-9844-8B&p=197971&viewfull=1#post197971
http://www.audioheritage.org/vbulletin/showthread.php?24463-Model-19-Crossover-Help&p=246630&viewfull=1#post246630

http://www.audioheritage.org/vbullet...l=1#post128826
http://www.audioheritage.org/vbullet...l=1#post128689



In the honor of our respectable member ZILCH, I would repeat his words:
"..Well, there it is again, I must say!

I worked quite a bit in the Valencia thread with trying to add a tweeter to 811B, and it just didn't happen worth a poop until I mounted a small one inside the horn mouth itself, and even then, there were issues, but none so major that, using this approach, Jackgiff was able to integrate one successfully. You're hearing substantially what I heard, most likely: standing separate, an add-on tweeter sacrifices coherency, and it's quite audible.

You've also found, as I did, that the 811B horn supports VHF, and with even the modest compensation provided by the N800F crossover, 902 will play fully out through 20 kHz. If you move up and down, you'll find that response is somewhat beamy, but the beamwidth is at least 30° vertical, and JBL's UHF drivers like 2402 and 2405 are about the same. The horn needing to be at listening height in order to hear the VHF adequately is the compromise. Bottom line on which it would appear we agree: Two way is better. Make it work.

What first struck me in these most recent measurements is the nearfield LF response. Compare what you measured to the simulated voltage drive of the N800-F, the blue line here:

http://audioheritage.org/vbulletin/s...2&postcount=55

The filter has assumed control of the woofers, and the response is flat as Nebraska. We're quick to criticize Altec engineers for their apparent cavalier approach in using this 16-Ohm crossover with an 8-Ohm load. Here, again, is evidence there's more to Altec designs than might casually be observed; it's US who are the fools.

Tuning now to the HF, generally, with the attenuation at "2" you're still playing that too "hot," by as much as 5 dB, perhaps. Crank it down for better balance. Watch what happens on the RTA display as you do that. The HF should be just slightly lower than the LF for optimum balance. That's encouraging, because it says there's sufficient headroom for a better compensation contour, which I will suggest below.

We again have a notch at 3K15. Let's find out if it's real before doing anything about it. Two suggestions: get that on the display again, and then rotate the horn slightly off-axis, so that the mic is aiming in the first open area off center, i.e., not at the central vane, which may be shadowing that frequency, or generating reflective interference.

Second, lay several layers of fiberglass insulation (or a thick fluffy comforter, folded) on the floor between the speaker and the mic, 6" minimum, paper only on the bottom layer, against the floor. We may be looking at a cancellation due to floor bounce at that frequency. That's the first reflection with a different path length (think inverted triangle,) and it WILL interfere with the measurements.

If neither of those measures mitigates the notch, and you don't discover something else which does, that notch is then coming from the driver/horn, not the filter, and it should not be there. Order up a pair of the Radian diaphragms for these drivers from Parts Express, install one, and compare the response measurements.

There's one more thing I'd like you to try the next time you set up for measurements, and that is to disconnect one of the woofers and see how that alters the total system response. You'll have to crank down the HF more to restore optimum. Do nearfield measurement on the single woofer also. I'm suggesting you try this because there's a simple way to use the second woofer as a "helper" to augment the LF response at the low end.

Finally, with respect to optimizing compensation, Altec used the "T" filter in later iterations of these "Pro" monitor products as well as in Model 19. The schematic differs from M19 in that it does not rely upon a connection in the LF filter path, and thus may be used independently. I'll draw that up and post it here. You may want to build both the LF and HF sections, so you have yet another LF option to try. We can almost certainly improve upon the HF response N800-F is generating in your system.

Thank you again for performing these tests and posting your measurement results. Know that you are contributing to expanding the knowledge base regarding these vintage Altec products and designs, and it is appreciated....

Edit: Model 19 crossover with N604-8H VHF attenuation:..."





The network You have presented us can be dangerous as it passes LF frequency to the 2446, that can destroy its diaphragm.

regards
ivica

[1audiohack]

Hi Jennifer;

I have that for the 2360, but I am traveling for 10 days so, if no one comes up with it by then, at least you will have it then. I will see if I can find it in my down time in the mean time.

All the best,
Barry.

[Jennifer]

"The network You have presented us can be dangerous as it passes LF frequency to the 2446, that can destroy its diaphragm. regards ivica"

Yes Ivica, this is quite obvious. The network as illustrated does not include a crossover or protection capacitor. THIS is just the EQ portion to apply frequency response correction to the bi-radial horn, and in that capacity, it is just my starting point, yet to built and measured. It represents the first starting point to make the horn/driver have improved frequency response compared to raw flat response drive, and after that, the other functions will be addressed.

Your comment does bring up an important point,...for years both on this forum and others, there has been discussion about including protection high-pass caps or not. Electronic crossovers and thumpless amplifiers has made it possible to direct drive compresssion drivers for many years now with reasonable safety, and many people in both recreational and commercial sound do direct couple when using line level crossovers and multiple amplifiers. In my case, I will be using a tube type amp with an output transformer that cannot pass any DC to its load. The input to the amp will be pass banded by active line level crossover at 24dB/Oct Linquitz Riley slopes. Even with this low-risk setup, I do subscribe to the traditional inclusion of protection capacitor. In my case, I do not know what the value for that part will need to be yet. I will not be able to measure the actual impedance of the horn/driver as a system until the compensation network is final and in place. The actual impedance is needed to select a capacitor value, and in addition, it will need to be sufficiently large a value so as to not introduce apprecaible phase shift added upon the phase of the line level crossover, and it will need to be sufficently small so as to limit any low frequency noise that can cause damage. Until I know what the crossover frequency will be and what the impedance is, that will remain undefined. Once a value is determined, it will likely be implemented as a split cap with DC bias, as that usually has improived sound over a single cap that is not biased.

It is my 'hope' that I can build a 2 way with the 18" JBL woofers running high enough to function well with these large horns. If the integration becomes a problem, then I will be in the market for a pair of 8", 10", or perhaps 12" midrange drivers. I am not yet at that bridge to cross. However, for the center 'dialog' channel [ by necessity it has to be much physically smaller ] I will be using a 2404h as the high frequency unit...as this needs to be crossed in no lower than 5KHz, and preferably a bit higher, I may be looking for the perfect 8" or 10" sooner than I think, and using the same mid range driver in all 3 front positions would provide a certain consistancy to voicing. We shall see. I would prefer that for the movie system, to be able to keep it simple and 2 way for the main L and R. These large horns are specified with a cut-off of something below 400 Hz range [ 375Hz comes to mind, ] , so can be low phase shift in its lower output region if actual use is 700Hz and up. I always try to stay about an octave above rated cut-off frequency of any horn for all the reasons that have been discussed and anaysed to death for decades.

The links you provided to discussion of the Altec 811 were interesting to me, in that back in the winter of 1968/1969, I built my first 2 way speaker with those in the high pass, in conjunction with JBL D-130 woofer. At the time, the JBL high frequency units all needed an acoustic lens to work. The 075 was never used with a lens, but I did not like its beamy high energy sound at all. The 175 and 375 on various JBL horns all needed a lens to create dispersion. I searched for alternative that couid be used without a lens. I found the 500Hz Altec horn to have some beamy qualities that were not comfortable to listen to, though it was quite popular in sound reinforcment and high output theater systems back then. I found the sound was less probematic with the 800Hz model. The D-130 had sufficient mid energy that it would run OK with the 811. I have a vague memory of building the crossovers to center at 1.6 KHz, but it was so long ago, that is not a clear memory....it may have been higher. I do recall that I used first order on the D-130 and 3rd order on the 811....Experimenting back then was not easy as parts were costly for me, just a kid of 16 years. The D-130 resided in 14 cubic foot sealed infinite baffle, the 811 sat on top. I always wanted to try a JBL compression driver on the Altec 811, but never had the opportunity. I just used the Altec driver as supplied. Also one should note that very rarely back in those days, did anyone in the DIY community use fine tune EQ networks. Most just purchased pre built crossovers such as from the JBL line. If we built our own from caps and chokes, mostly it was just frequency dividing and we let the horn/driver do its thing going up to where it would just roll off.

I had a pair of Pilot mono integrated tube amps at the time, 6BQ5 push pull outputs, so maybe 9 or 10 watts. It was plenty....

[baldrick]

This is what JBL used for 2x2226 and 2446/2360:

[Jennifer]

Hmmmm I see they like the variable reactance of an inductor in parallel with the voice coil. In the case of keeping max total effeciency, I can see why they would do that... Some other JBL crossover examples I saw used a tapped inductor to change the value, allwing one X-Over to be tuned to different applications by changing strap connections. In my case, loosing some total energy is fine. We are starting with 116dB/1W/1m into what amounts to a living room space, not a stadium or performance hall. My rational so far is that with a build-out series resistance and a resistor parallel to the voice coil, I can get some attenuation, and flatten the imedance change magnitide with the parallel resistor, making any network upstream a bit more linear in its performance, with a less variable load. One other side effect of the R in parallel with VC is to provide some degree of local damping, at least in a theoretial sense. With the inductor in parallel with voice coil, we arrive at in essence, a variable resistance, low R at lower frequency, and higher R at higher frequency. I always worry about time domain effects of reactive components, absent in a resistor. However, with the inductor, there may well be some energy loss in the area of the hump as it presents a lower impedance bypass of the VC at decending frequency...This may well be worth some investigation by testing actual results, even if it not needed on the arguement of total higher effeciency in the upper range. If it eliminates the trap network to create the droop, or at least reduces the magnitude of effect the trap needs to create. as an overall sound quality, it might well be worth it. I notice the spell checker is not functioning..Please accept my spelling errors if you find any, it is not really deliberate, nor a sign of gross ignorance, just of fast typing and not taking time to export to a spellcheck and then back into post reply. I shall add experimentation of inductor in parallel with VC to see how it behaves... I do very much appreciate the input, this is how we learn, exchanging ideas and solutions....

[JeffW]

The schematic in #5 shows two 2226 L.F. and a single 2245 L.F., not sure if the 2245 L.F. should be 2445 H.F. or what, just a heads up.

[Jennifer]

The schematic in #5 shows two 2226 L.F. and a single 2245 L.F., not sure if the 2245 L.F. should be 2445 H.F. or what, just a heads up.

I think its a typo...I have seen a few errors here and there in the old supporting lit. Graphics dept. not engineers. Obviously the compression driver is going to be either 2445 or 2446 depending on when built, and there is one of them following a high pass. The important part is to read the schematic, and hope those parts values are correct!

[Jennifer]

http://www.jblproservice.com/navigat...chematics.html
Just discovered this page....going to spend some time looking at a LOT of crossovers in the next few days.

[ivica]

Hi Jennifer,

Just for experiment

regards
ivica

[Jennifer]

Very insightful.....plus it includes an actual high pass crossover element. I have to get busy now and build up a few of these to try and measure them out. Friend of mine has Audio Precision System Two... I bring one of my Microtech-Geffel instrumentation capsules on a Josephson mic body, and a Millennia Media HV3D mic pre....just stuff from my recording rig...but we can make some decent measurements with it all out on his deck, open to the sky. I am hoping for pretty flat to 15KHz, and do not expect any higher as the throat will not support it.
.
THANK YOU for posting the schematic, it is one that I had yet to come across...it shows yet another solution ..I may end up with a combination of this and my original, borrowing some of the good ideas here...or even pretty close to this solution...

To help those not yet fully fluent in schematic, here is a basic functional decode.

C1, C2, L1, R9, form the high pass 'crossover', based on a classic 3rd order, modified by the R9.

C3, and associated resistors R1,2,3,and 4 form the high frequency boost, and a little bit extra attenuation in the stop band via the resistance to the minus side.

L1, C7, R12, and R5, form the mid droop curcuit to offest the slight natural hump in the horn natural response

R7, R8 form a voltage divider to attenuate the final output, with R8 doing double duty in parallel with the voice coil to reduce the magnitude of the natural inductive VC impedance rise, and also to provide a touch of local damping.