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.

[hjames]

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.

Dang - didn't we start here, days and days ago!
You get what you pay for, and someone bought a cheaper replacement diaphram ...

[deafbykhorns]

Yes, someone bought a cheaper diaphragm but I wouldn't expect it to be 10db down in sensitivity. I would call it cheap chinese garbage, but look at the bright side, it may have a higher power handling rating or maybe not.
I ordered the original diaphragms

[louped garouv]

it may have a higher power handling rating or maybe not.

how much power were you thinking of running through them?

[deafbykhorns]

Well, my username might be misleading but just the typical 1-20watts thru a network. I blow out the cob webs about every 2 months and hit it with about 300w thru a MC352 for about 30 seconds. Enough to piss off the wife when all the knick knacks go flying off the entertainment center. The output is not good enough with the current diaphragm for normal listening but would probably be fine in a PA system.

[scott fitlin]

Yes, someone bought a cheaper diaphragm but I wouldn't expect it to be 10db down in sensitivity. I would call it cheap chinese garbage, but look at the bright side, it may have a higher power handling rating or maybe not.
I ordered the original diaphragms

I agree, 10db is REALLY excessively low. My after markets, which are the SAME as what you have are NOT 10db down, either. They just don't sound like GENUINE JBL, and not good enough, either.

However, when the after market diaphragm was installed in the 2404, if it isn't sitting in precisely the right spot in the gap, there goes the sensitivity down the tubes. a millimeter or two will do it, small though this amount may seem. Or perhaps, when the person installed the diaphragm, they weren't careful, and nicked the windings in the gap, causing a short, where the VC is still conducting some signal, but very very low. And, as someone else had suggested, if the adhesive bonding the VC former to the diaphragm has let go, and part of the VC former is just flopping in the gap loose, THAT would definitely do it. I had a 2402 bullet tweeter with it's original diaphragm from 1983 with this exact condition a few years back, and IT PLAYED, just at an unacceptably low level. When I disassembled the 2402 I found half the VC former unattached to the diaphragm, and I was surprised it worked at all.

On another occasion many years ago, back in the 1980,s my system had ALTEC 15,s. And I had a couple of woofers reconed, I run a commercial system, and occasionally we blow a woofer. So I had the pair reconed at the service center we use to use in Manhattan, NYC, and the recone kits were genuine ALTEC, but whoever did the work must have had a bad day, or whatever, and one woofer of the pair I had serviced just was dead sounding. Since both woofers were in ALTEC 816 cabinets, side by side, it was easy to hear. And I put my fingertips on the cone of the woofer that played very low, particularly in the midrange response, and ever so slightly pressed the cone back a bit, while music was playing. RIGHT AWAY THE LOW MIDS CAME BACK! And when I say I pressed the cone back EVER SO SLIGHTLY, I really mean SLIGHTLY! So, one of two things, the person who did the work did not shim and install the recone kit correctly, or the kit was a defective kit. But, moving the cone back, maybe a nnth of a degree put the VC where it was supposed to be, and the difference in output was astounding! The store/service center reconed the woofer, again, no extra charge to us, and this time, it came back correct. But, YES a few tiny millimeters made all the difference in the world.

Now, your dealing with a JBL device, and a NON JBL part, and my guess, which most have already said as well, is the NON JBL part is NOT made to the exact size specification as the real JBL part. When you purchase genuine JBL diaphragms there is a small pamphlet enclosed in the packaging. The pamphlet says " Centering of the voice coil within the magnetic gap requires specific test equipment and training and is critical to the performance and reliability of this product. The enclosed part is made to critical tolerances. Damages resulting from improper installation by anyone not authorized by JBL will not be covered by the JBL warranty.

This tells it to you verbatim, Centering and alignment of the voice coil in the gap is critical to the performance of the unit! There are a few more sentences in the pamphlet, but I posted the part I feel is MOST relevant to the issue at hand, PERFORMANCE! JBL says the positioning of the VC in the gap is critical.

So, when you get your JBL parts, and either have it installed professionally, or DIY, and it is done correctly YOU will definitely hear two things. One is as long as the VC is where it is supposed to be, your 2404 will produce the proper amount of output, and two, you will DEFINITELY hear the magic of the JBL sound.

And after this, you will probably say the same things WE say on this forum, USE JBL PARTS IN JBL PRODUCTS, PERIOD!

It's CRITICAL!

[deafbykhorns]

Well, received my replacement JBL parts today, all I can say is NIGHT AND DAY difference. These things sound sweet and measure right at 105db at one watt as specified. I don't believe for a minute it was alignment issues, conclusion: chinese parts SUCK!

[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?