JBL 2404H Low Output

[deafbykhorns]

Hello, I'm new to the forum but a veteran on a couple other forums. Just purchased a pair of 2404H baby cheeks. I am upgrading some Khorns using the JBL horn drivers. The original tweeter is a EVT35 style and has a 104db sensitivity. Now the 2404H has a 105db rating which should make it hotter, it is not. After removing the lense, I found an aftermarket pair of diaphragms. Could this be the cause of the low output? The DCR is about 6.4 ohms which tells me these should be 8 ohm impedance. They look exactly like THESE on ebay with the same number.
Connected to my networks, both are at least 3-5 db down from the K77/EV T35 tweeters.
Are the generics that far off? I have some test equipment to verify this but its obvious the output is much lower.

[hjames]

Hello, I'm new to the forum but a veteran on a couple other forums. Just purchased a pair of 2404H baby cheeks. I am upgrading some Khorns using the JBL horn drivers. The original tweeter is a EVT35 style and has a 104db sensitivity. Now the 2404H has a 105db rating which should make it hotter, it is not. After removing the lense, I found an aftermarket pair of diaphragms. Could this be the cause of the low output? The DCR is about 6.4 ohms which tells me these should be 8 ohm impedance. They look exactly like THESE on ebay with the same number.
Connected to my networks, both are at least 3-5 db down from the K77/EV T35 tweeters.
Are the generics that far off? I have some test equipment to verify this but its obvious the output is much lower.

Well, JBL replacement parts are speced to perform the same, the other brand is just an unknown. Its hard to say for sure - but that'd be my guess.
Its hard to know what the specs of the aftermarket product is.
They may look similar, but you pay for the sound, not for the looks.

[jcrobso]

http://cgi.ebay.com/Diaphragm-JBL-24...item2ea17aacee

The JBL ones are expensive, but you get the quality.
http://www.reconingspeakers.com/prod...phragm-16-ohm/
One you get a good diaphragm you will like the 2404 over that EV35.
I have a pair of home made "K" horns loaded with JBL, love them!
And Welcome!!!!

[deafbykhorns]

I just spoke with the original owner, they purchased these from the site link you mentioned.
That distributor may of used a different supplier a couple years ago

[pocketchange]

I've noticed your experience too and have come to the conclusion that the output of the 2404 is a great deal smoother with a much improved pattern.
I'd suggest enjoy them for awhile and see if they don't grow on you with their over all presentation.
I replaced a dia. in mine (w/the high priced spread) to confirm your same observation and didn't notice any differences other than the (much) improved presentation...
BTW, the thread to the 2404 JBL dia (being 16 ohm) replacement is not correct as the 2404 is an 8 ohm piece

[JeffW]

BTW, the thread to the 2404 JBL dia (being 16 ohm) replacement is not correct as the 2404 is an 8 ohm piece

You might take a look at This thread to clear up any misconceptions.

[deafbykhorns]

I did read that thread and was concerned someone may of mismatched the magnet and horns but it doesn't appear like the phase plug is hitting the diaphragm. I was thinking that might be the issue with the low output after reading about the 2402

http://www.soundspeakerrepair.com/sp...+Instructions/

[jcrobso]

I've noticed your experience too and have come to the conclusion that the output of the 2404 is a great deal smoother with a much improved pattern.
I'd suggest enjoy them for awhile and see if they don't grow on you with their over all presentation.
I replaced a dia. in mine (w/the high priced spread) to confirm your same observation and didn't notice any differences other than the (much) improved presentation...
BTW, the thread to the 2404 JBL dia (being 16 ohm) replacement is not correct as the 2404 is an 8 ohm piece

If you can't get the JBL 8ohm part you can use a 16ohm, but you need to put a 8ohm 5W resistor in parallel with the 2404 so the X-over sees 8 Ohms.

[louped garouv]

If you can't get the JBL 8ohm part you can use a 16ohm, but you need to put a 8ohm 5W resistor in parallel with the 2404 so the X-over sees 8 Ohms.

if the filter is designed for a ring radiator, why would he have to change the value....

although the focial may indicate a certain 'ohm' rating, aren't they functionally equalivent -- despite the focial?

[JeffW]

if the filter is designed for a ring radiator, why would he have to change the value....

although the focial may indicate a certain 'ohm' rating, aren't they functionally equalivent -- despite the focial?

That's what the link I posted pointed out. All the diaphragms for the 2404 and 2405 are the same DCR. The diaphragms for the 2402 are the same DCR, but different material. If you put a 2402 diaphragm in a 2404 assembly, they call it a 2404H-1.

There was another poster recently wondering why the "16 ohm" versions of these ring radiators commanded a higher price on Ebay than the "8 ohm" versions. Since, other than the magnets on the earlier Alnico version, there's really no difference in the diaphragms (in the 2404/2405 family) that would make any difference one way or another. Buy the cheaper "8 ohm" models and slap new diaphragms in there...that you should do even if it's a "16 ohm" version.

[deafbykhorns]

The part number is D16R2405, they dont have a D8 part number so I assume they are all 8 ohm since the DCR measures about 6.4
"Actual transducer impedance will vary depending on diaphragm loading" Can someone explain this?
I think the 16ohm/D16R2405 are higher priced since they are factory replacements?
Anyways, my only concern is could the magnet be a 075 magnet which would require the masking tape shim. Is this possible?
I'll mic these over the weekend with a signal generator to check the real sensitivity. Maybe my hearing is shot and the 2404 is doing its job and the old K77 was not. It's almost sounds like the K77 has a lower crossover point compared to the 2404H

[JeffW]

The best advice I can offer is to just buy the JBL D16R2405 diaphragms and install them. They'll work without any masking tape shims and make the drivers perform as designed. The reason you got a JBL driver was so it'd sound/perform like a JBL driver, and the way to make that happen is to put a JBL diaphragm in it.

The combination of diaphragm, air, frequency, and horn contribute to the impedence of the driver in operation, and you can see all this with an impedence curve. The same diaphragm, in the same driver motor, with a different horn attached, will have a different impedence and impedence curve thru its range of operation. But they all start with the same DCR.

Here's what you want

[deafbykhorns]

I tested the tweeters this morning using a signal generator, RTA software and a friends calibrated mic/preamp. After sending a 4500hz signal to the 2404h, it was obvious something was really wrong with this tweeter. I inserted the Klipsch K-77 and this tested very close to the 104db at one meter. I then reinserted the 2404H and this tweeter was almost 10db down below 94db at one meter. This was the case with both tweeters. Keep in mind both of these have had the diaphragms replaced with a reputable suppliers parts(soundspeakerrepair.com).
Something is obviously wrong with these tweeters and I find it hard to believe its the diaphragms, they just cant be that far down. The measured DCR is within specs so there must be something else going on. I wouldn't think the magnet could be that far out of spec and its consistent with both tweeters.
Could the magnets been mixed up on a previous tweeter replacement using an 075 magnet that requires shimming?
I can purchase the above JBL replacements for $85ea from a fellow JBL dealer but concerned about the magnet assembly.

Update: I loosened the phase plug off the diaphragm and didn't notice any change.

[1audiohack]

Just to back up a bit, the magnet/motor assemblies including the top plate and pole geometry are all the same on all 13 of mine. I bought two of them new when these first came out in the mid / late 80's if I remember correctly, and the last one out the door of JBL not to long ago on the etent sale sight.
I bought seven of them new in all and got three variations. There are two different size phase plugs, one is 1.600" at the base, the other is 1.715". Then of course there is the D8R075 and the D16R2405 diaphragms for a possibility of four combinations, one of which I have never seen from the factory in my new stuff, which is the 1.600" plug withe the D16R2405 diaphragm.

[JeffW]

Keep in mind both of these have had the diaphragms replaced with a reputable suppliers parts(soundspeakerrepair.com)...

Something is obviously wrong with these tweeters

Asked and answered at the same time?

Good luck.