2440 vs. 2441 Diaphragm in 2445-driver

[JoeNelis]

They absolutely will, with one caveat, that there is no large discrepancy in the phase plug height and or diaphragm height.

Often there will be a plus or minus number on the driver top plate made with a felt tip marker and one written in ball point pen inside the the voice coil on the former. These are matched up fairly closely when new.

The maniacs among us will buy a dozen diaphragms and mix and match with a dozen drivers to get as close as we can get.

If you are just doing a couple you get what you can get. The vast majority of the time they are close enough, for the majority.

Barry.

Speaking of trying different diaphragms i have 3 jbl 2440/2241 and when my friend took the cap off two of the units had a 120mm width on the locator pins and the other one has 130mm ??? i have not seen or heard of this width with the pins.

The stamp number is 18 so maybe one or the first ever produced.

[ivica]

Thanks a lot Are you shure both these diaphragms will fit in my 2445 without any trouble?

Hi Dr.db,

Here on the Forum, there are much, much more experienced members then me, as

http://www.audioheritage.org/vbullet...hp?285-subwoofhttp://www.audioheritage.org/vbullet...hp?285-subwoof

http://www.audioheritage.org/vbulletin/showthread.php?35014-4-quot-coil-Nd-driver-history-revisited&p=354792&viewfull=1#post354792

".....Well there are a few tricks for each mounting method - in general for the older pin diaphragms drill out the locating holes from 1/8" to 9/64" []3.6mm] and that should give you plenty of room to "wiggle" This is a common procedure around here.. For the shoulder types, the dia is held in position at each mounting screw position against a small portion of a shoulder that is milled into the top plate. Take a NEW, decent size tool steel *right angle* edge ( as would be found on a wood chisel SIDE or machinists block ) and shave down the diaphragm where it meets this shoulder. DO NOT USE A FILE, SANDPAPER, KNIFE EDGE, LAWN MOWER or something LAYING AROUND...Buy it NEW if you aren't a machinist! Because slight offsets and material size differences when making the diaphragm assembly happen ( it is a sandwich if you look close ), there are burrs / waste material / etc etc. By shaving down these areas ( ALL EIGHT ) the diaphragm can move around. Bingo...be sure to remove the burrs you CREATE ! NOW THAT YOU KNOW THIS - it is IMPORTANT to have a low distortion oscillator to align the diaphragm - AND THE DRIVER must have a nominal air mass load at the exit otherwise you will get false response / harmonics that will FOOL you.. NOTE: methods for aligning the NEWER Nd drivers with the dia glued into the back cap are not yet hacked. Someday I will find a need but HELLO, they never blow up right?? Anyways I made a wood box with various holes with wood dowels for guides and lined it with insulation.. stuck a cheapo microphone in the side and connected to the oscilloscope and compared in/out. Wearing earplugs and headphones you can actually hit a driver with some decent power to see if there's any breakup but it REALLY pissed off the cats. Worked great until I gave it away to a tech and never bothered to make another. Hmmm...Maybe I have a market here......."


who can give You very useful advice, but if you have 2445, I would expect that using any of the mentioned diaphragm would not make You any great trouble. Here, on the Forum, You can find detailed instructions how to fix the diaphragm assembly to drivers body.

regards

ivica

[Dr.db]

Often there will be a plus or minus number on the driver top plate made with a felt tip marker and one written in ball point pen inside the the voice coil on the former. These are matched up fairly closely when new.

You wouldn´t have a picture of that, would you ?

[more10]

other one has 130mm ??? i have not seen or heard of this width with the pins.

Could be a 2482.

[Dr.db]

They absolutely will, with one caveat, that there is no large discrepancy in the phase plug height and or diaphragm height.

Often there will be a plus or minus number on the driver top plate made with a felt tip marker and one written in ball point pen inside the the voice coil on the former. These are matched up fairly closely when new.

Is this a problem that adresses all JBL 2" drivers and diaphragms or especially the 2445 and D16R2451



And thanks ivica for the diy-guide

[Dr.db]

BTW; is the advantage of aluminum diaphragms over titanum dia´s just in the high freq. area ?
Because the ti dia´s as the 2445 start to break up into distortion in very high freqs and therefor sound harsh ?

Would there still be a difference noticeable when lowpassed at about 9khz when used with a 2405 on top ?
Would a 2445 ti diaphragm sound smooth just because it is lowpassed

[1audiohack]

Here is a look into a brand new 2450.

The top plate shows -4. The diaphragm is a zero, I would have hoped it would at least have been a -2.

This driver has not been powered up yet so I don't have a PWT TEF sheet on it.

In my testing this combination will in my opinion result in slightly poorer HF response. The extra clearance to the phase plug will allow it to play lower louder.

The bare minimum diaphragm install requires a signal generator and an amp you can trust, a Crown D45 works great and buzz test it at 300Hz with increasing volume until you are satisfied that the coil isn't touching in the gap and the diaphragm isn't contacting the plug.

Here is a little audiohack technique that may disturb the masses. Simply don't do it if you aren't comfortable with it. Do not do this with Be diaphragms!!!

A JBL diaphragm is in close enough proximity to the phase plug when installed that you can touch/push on it gently with a finger tip until it easily touches the phase plug. If it is buzzing while testing you can run your finger around the perimeter and find where it is in closest contact and figure out which way you need to move it. Most of the time I have to file the outer diameter of the aluminum rings that locates the diaphragm assembly in the top plate to move it around so that it is really centered.

I don't intend to get you in deep and get you paranoid or crazy about this but in my opinion this is the minimum required to get them right.

I take this a lot farther on the PWT while watching live via RTA while I push and pull and tighten the screws for spurious noise and bandwidth and with TDS measurements as a final validation.

As a note of experimentation, I have a pair of 2451's with JBL D8R475ND diaphragms that very smoothly go out to 16kHz. This was accomplished via machine work to get the diaphragms very close to the phase plug. The down side to that is they won't play super loud crossed over at 800Hz, they sound like breaking glass when the diaphragm hits the phase plug. They are great for indoors though. I have them on a pair of Woody's Y290's and they are magic.

This may be less than helpful and if it is, I am sorry.

All the best,
Barry.

[1audiohack]

BTW; is the advantage of aluminum diaphragms over titanum dia´s just in the high freq. area ?
Because the ti dia´s as the 2445 start to break up into distortion in very high freqs and therefor sound harsh ?

Would there still be a difference noticeable when lowpassed at about 9khz when used with a 2405 on top ?
Would a 2445 ti diaphragm sound smooth just because it is lowpassed

These big drivers are very linear and clean right up to 9kHz, about 9500Hz they go bananas. Cutting them off at 9kHz makes everything easy. You could just use a 2440 for that.

Barry.

[ivica]

Here is a look into a brand new 2450.

The top plate shows -4. The diaphragm is a zero, I would have hoped it would at least have been a -2.

This driver has not been powered up yet so I don't have a PWT TEF sheet on it.

In my testing this combination will in my opinion result in slightly poorer HF response. The extra clearance to the phase plug will allow it to play lower louder.

The bare minimum diaphragm install requires a signal generator and an amp you can trust, a Crown D45 works great and buzz test it at 300Hz with increasing volume until you are satisfied that the coil isn't touching in the gap and the diaphragm isn't contacting the plug.

Here is a little audiohack technique that may disturb the masses. Simply don't do it if you aren't comfortable with it. Do not do this with Be diaphragms!!!

A JBL diaphragm is in close enough proximity to the phase plug when installed that you can touch/push on it gently with a finger tip until it easily touches the phase plug. If it is buzzing while testing you can run your finger around the perimeter and find where it is in closest contact and figure out which way you need to move it. Most of the time I have to file the outer diameter of the aluminum rings that locates the diaphragm assembly in the top plate to move it around so that it is really centered.

I don't intend to get you in deep and get you paranoid or crazy about this but in my opinion this is the minimum required to get them right.

I take this a lot farther on the PWT while watching live via RTA while I push and pull and tighten the screws for spurious noise and bandwidth and with TDS measurements as a final validation.

As a note of experimentation, I have a pair of 2451's with JBL D8R475ND diaphragms that very smoothly go out to 16kHz. This was accomplished via machine work to get the diaphragms very close to the phase plug. The down side to that is they won't play super loud crossed over at 800Hz, they sound like breaking glass when the diaphragm hits the phase plug. They are great for indoors though. I have them on a pair of Woody's Y290's and they are magic.

This may be less than helpful and if it is, I am sorry.

All the best,
Barry.

Hi Barry,

Many thanks for explanation JBL hand written numbers on drivers body and diaphragm, and very instructive way of precise tuning its position.

Best Regards
Ivica

[Dr.db]

Thanks a lot for your great explanation!!

Is there any possibility to order diaphragms with a certain value written on it ?
Or do I really have to buy a bunch and sort out the best matching ones?

I guess this issue affects all 2"-compressiondrivers, doesn`t it ?

[Dr.db]

I´m still wondering if there is any benefit of using the 2441 over the 2440 when lowpassed at ~9khz?

The 2441 has a more extended freq.-range, but I think this ain´t important in my case as I have a 2405 on top....
But I have the westlake clones that are very close to the 2397. But as seen in widget´s graphs, they have less sensitivity than the 2397 above 6khz
So I would have to use a equalizer and add several db´s in the high-midrange....
The old style 2440 hasn`t extended highs, but has about 4-5db´s more efficiency from 6000-9000hz.
Do you think the 2440 would compensate the sacrifice in highs of the Westlake horns

[Lee in Montreal]

Thanks for sharing the diagram. Got me thinking. Maybe I shall remove my 2360a horns and reinstal my 2350 horns with 2441 drivers on Radian diaphragm. I can still eq the range over 10KHz... ;-)

Lee

[ivica]

Thanks for sharing the diagram. Got me thinking. Maybe I shall remove my 2360a horns and reinstal my 2350 horns with 2441 drivers on Radian diaphragm. I can still eq the range over 10KHz... ;-)

Lee

Hi Lee,

I think, (my experience and measurements), Radian 1245 AL , is not even good as D16R2441AL over 10kHz, if You make high resolution measurements, You can prove that. With Radian 4" diaphragm You can use it up to 10kHz, and over that use 240x driver....that is my suggestion.

regards
ivica