Uneven response on 2440 with new diaphragm

[Pellets]

Hi all,

recently I fitted new Radian 1245 diaphragms to my old 2440 drivers. The old diaphragms were battered and worn so I expected a change for the better. Well I can't say the new ones have made a big change and I tried to measure the response with may AudioTools app. The response looks quite ragged to me. Is this what to be expected?

I don´t have the standard H93 horn, instead I use the Selenium HL14-50N which some say is a better horn for this driver. Measured with pink noise through a 800/8K bandpass filter.

Best regards

[edgewound]

Hi all,

recently I fitted new Radian 1245 diaphragms to my old 2440 drivers. The old diaphragms were battered and worn so I expected a change for the better. Well I can't say the new ones have made a big change and I tried to measure the response with may AudioTools app. The response looks quite ragged to me. Is this what to be expected?

I don´t have the standard H93 horn, instead I use the Selenium HL14-50N which some say is a better horn for this driver. Measured with pink noise through a 800/8K bandpass filter.

Best regards

Couple things could be going on.

Did you install and test with a sweep generator and listen for anomalies? Did you use any of the included shims? Have you ever had the magnets recharged? Freshly charged magnets can make a huge difference.

[Earl K]

The jaggedness might just be caused by the app's resolution when using Pink Noise.

Maybe you need a better TEST setup ( like REW and a UMIK1 USB mic ) ?

REW works on both Windows and Mac ( and is share-ware >. essentially free ).

Also, try your 2440/Radian combo on a different horn ( if you have one ) to get a sense of changed perspective ( iow; which ripples are horn induced and which are from the driver/diaphragm combo ).

Here's a pretty ancient trace ( made using a Sine Sweep in ARTA ) of one of my 2482 drivers loaded with a Radian R1282 diaphragm and mounted onto an H5038 ( Paragon ) horn.
- Note#1; there's is an 8 ohm resistor with a 3uF cap paralleled to it , both in series with the driver ( this RC combo offers a bit of HF compensation ).
- Note#2; no mic calibration was loaded back then > so the HF is exaggerated by about 3db too much above 10K .




I think my hi-rez curve is a bit smoother than yours.

[Pellets]

Thanks Edgewound and Earl K for your responses. I´ll try to explain better:

The new diaphragms came with shims. I contacted Robert at Radian who said that if the old diaphragms didn´t have any shims then don't use them on the new ones either, so I didn't.
I ran a frequency sweep from 350-3000 Hz through the coil during the assembly and everything sounded fine. The drivers have not been recharged and they seem to have been around for some time. I spent a long time cleaning gap and phase plug.

Test setup: I used pink noise through an electronic L/R crossover with 24 dB slopes and a passband 800-8 kHz. Then through a Rotel power amp to the unit. I picked up the signal with a Pearl studio condenser mic at 1 meter and fed the signal to the SMAART TOOLS app in the Audio/Sound Toolbox on my computer. This is basically a fast RTA which I set at 1/12 oct smoothing with a 8192 FFT size.

What concerns me is the almost 10 dB variation in the passband.

I will try another horn when i can find one. The Selenium horn is not foreshortened and should be able to deliver down to at least 800 Hz, but I understand what you mean that the horn itself can introduce ripples.

And I will certainly try out the REW software to see if the results get better (or my understanding of it)!

Best regards

[withTarragon]

Before you get too caught up with REW, I would go back and try what was mentioned earlier using tone sweeps and listening.

My limited experience has been with slightly newer drivers (JBL 2445 & 2446) and using JBL diaphragms. What I found was 1) even there were no shims previously, I had to fabricate one using thin paper (to prevent it from sitting too deeply). 2) using repeated tone sweeps, I had to torque the screws very evenly to see if the response was even. I then had to go back and try torquing with a bit more force in one quadrant vs another. You can actually turn the screws for a loose fit and then simply push on the diaphragm while the tones are sweeping. This gave me the ballpark positioning.

Two observations 1) when it was sitting too deeply, there was a harshness (harmonic distortion) at the lowest frequencies (quite audible). 2) when the diaphragm was not centered, there was low pass filtering effect. The output was decreased overall, but even more decreased at the higher frequencies. In your case, a 10 dB difference would be "audible" as about "half as loud", Ultimately REW will verify this.

Two comments, 1) In the past, some said these are self-centering diaphragms and you do not need any adjustments using tone sweeps and ultimately REW. That is not the case for the 2445 / 2446 units. The 2440 is older so my guess, and it is only a guess, you may be having the same problem. 2) this is a tedious back-and-forth process and will take some ingenuity and dexterity (I assume the pros have some sort of jig to help out). It may not go quickly, so it is much faster to do it with tone-sweeps and your ear for the initial positioning. Stopping to do REW measure every time would take forever. Save REW for the last stage.

Also, I know you mentioned that you cleaned out any debris (and I assume you did not use composed air). Are you confident you did a thorough job?

good luck,
-Tom

[grumpy]

I don't know... if I eyeball average, it looks like a quite expected first cut at a phone measurement.
Definitely room for both kinds of tools for the task at hand.

[Pellets]

Hi again,
I´ll try to wrench the monster out of its box this weekend and have a go at the alignment and the shims issue. Radian said that the shim is mostly used by those who need a greater clearance between diaphragm and phase plug which might be necessary at higher power levels. The high frequency rolloff will then be lower.

When you fit the diaphragm there are two locating pins securing it into a centered position. Maybe there is some play there anyway. But you should be able to hear some unwanted buzz when you run the frequency sweep and it's not properly centered, otherwise I don't now how to proceed with this.

I took my time to clean the driver before installing the new diaphragm. The gap is wide enough to be inspected with a light and magnifying glass. I was mildly surprised to find all that debris in the gap though!

So hopefully I´ll be back with some improved response curves soon.

Best regards

[toddalin]

I assume that your measurement was conducted in an actual habitable room with furniture as opposed to an anechoic chamber and this can make a big difference.

[Pellets]

Yes absolutely. The 2440:s sit in Olympus cabinets in my living room. They are not easily moved about. I measured at one meter distance from the midrange horn without the grille. The 2440:s are a devil to disassemble but I will do it.

On the other hand there is this school of measuring real close to the radiator thus reducing the room effects. It's easy to check whether this is of any importance or not. I´ll come back to that.

Best regards

[Pellets]

Hi again.
I got the driver and horn out of the cabinet today and I opened it up for inspection. The gap was clean and after replacing the diaphragm I ran a frequency sweep which was OK. There is no way to move the diaphragm assembly once it is set onto the locating pins.

I made a first test with pink noise at one meter distance and one close up to the horn mouth. See attached graphs. After that I fitted the shim that came with the Radian diaphragm and ran the test again. To me the response looks much worse with the shim. I have adjusted the output level between the readings in case you wonder.

It seems now that there is a variation of about 5 dB or so in the passband. Maybe that's as far as it goes with this driver/diaphragm. What do you think?

Best regards

[Mr. Widget]

If the diaphragm is snug on the pins and there is no buzzing, you are likely properly centered.

As for the the apparent choppy response, have you tried other horns? This type of response can easily be caused by the horn itself. Most horns are far from linear.


Widget

[grumpy]

what are you using for measurement settings? averaging? (yes? or 4-8s delay) "Advanced FFT settings"(Hamming window, 50% overlap)?
There's an unusual very low-resolution look to the plot that has me wondering about the settings...
The FFT plots from the StudioSix AudioTools app on my phone looks quite similar, but much better resolution (including when noise is used as stimulus).
I expect your driver is fine, and there is something going on with the measurement.

[Odd]

As recommended earlier here download REW (free)
Support Norwegian here
Support Forum

[Pellets]

Hi again.
Sadly I don't have a 2" horn available right now. I can guess that neither the H93 nor the Selenium are perfect, and as soon as I can I´ll buy - yes, what? Would a horn like the 2380 fit? I read somewhere that the throat geometry is different between old and newer JBL drivers.

The difference in response between closeup and one meter distance are maybe due to room effects. It actually looks better at one meter though.

As for the SMAART Tools setup - I don't have the FFT windowing selection feature and I selected a FFT speed of 8192 because it was recommended as a good tradeoff between accuracy and speed. Nor do I have an Average decay setting - I have used 6 seconds delay but maybe I should have tried up to 10 secs (Infinites seems to save the top readings). For readout I used the 1/12 octave RTA line setting. Perhaps it's better to go for the solution that Earl K and Odd recommend with the REW software.

It's interesting though that once I got the driver/horn out and onto the top of the cabinet the response became notably smoother. But I can't have it like that, people here already think the speakers look a bit overwhelming.

Best regards

[Pellets]

Hi again. It took a while to sort out the REW software but now it seems I have a grasp of the functionality. After some calibration I ran a curve of the 2440 through my electronic crossover (800Hz-8k@24 dB/oct).

The settings in the REW RTA were 1/12 oct 8 average 50% overlap. I used the PN pink noise as recommended.
Here is a picture of the response. This time though the driver/horn was mounted in the cabinet and not free standing as in the previous pictures.

The curve looks quite similar to the previous one apart from the very deep notch at 2.2KHz or so - this could be seen on the previous curves but not that deep. Maybe it's exaggerated by the baffle. Anyhow it seems that the response is quite ragged with at least 5dB variation in the passband. What can be done? Can I measure better?

I'm on the hunt for 2311 horns but they are very scarce. The 2380 is too big for the cabinet. Any ideas?

Best regards