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 (http://cgi.ebay.com/Diaphragm-jbl-2404-H-2404H-baby-cheek-tweeter-JBL-/280523322508?pt=LH_DefaultDomain_0&hash=item41507e348c) 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 (http://cgi.ebay.com/Diaphragm-jbl-2404-H-2404H-baby-cheek-tweeter-JBL-/280523322508?pt=LH_DefaultDomain_0&hash=item41507e348c) 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-2404-2405-Peavey-HT94-8-ohm-P-10-914-/200277667054?pt=LH_DefaultDomain_0&hash=item2ea17aacee

The JBL ones are expensive, but you get the quality.
http://www.reconingspeakers.com/products-page/diaphragms/jbl-diaphragms1/jbl-2404-d16r2405-jbl-diaphragm-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 :confused:

[JeffW]

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

You might take a look at This thread (http://www.audioheritage.org/vbulletin/showthread.php?23869-075-2402-076-2403-2404-077-2405) 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/speaker-parts-cp/JBL-2404-Video-Instructions/INST/Installation+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 :confused:
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.

[JeffW]

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.

Do any of your combinations need masking tape to work? :D

[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.

Two of the used ones I bought had aftermarket diaphragms in them and the sounded different than all my others and measured not good. The times I have seen low output
(without obvious reasons) have been voice coils partially un bonded from the radiating element or coils/formers in cotact somewhere in the gap, that just knocks the efficiency and fidelity right out of them. They don't move far enough to click and pop from the stiction like a 2 or 4 inch drive will so you are unlikely to hear it.
If you can take a good hi resolution impedance measurement these have a well defined peak at Fs if they are not dragging in the gap.
If you don't have all the stuff to measure and test, just bite the bullet and send them somewhere that does, look for a shop that can give you a proof of performance sheet when they hand you the bill.

[1audiohack]

No masking tape required! All four combinations require no such buchery.

Sorry I am on the road doing this from an IPhone, I don't know why it sent it out twice partially. No I'm not driving at the moment.

[Earl K]

deafbykhorns

Perhaps your 2404s are fraudaulent copies ( knockoffs carrying a bogus JBL label ), as the poster in this 2445 thread (http://www.audioheritage.org/vbulletin/showthread.php?28758-JBL-2445_46-frq.response) discovered .
- Copies often use lighter weight magnets to reduce costs // resulting in less output .

- "Fraudaulent" ( if they aren't OEM JBL ) but have been stickered with a JBL label .
- Here in North America a seller can be brought up on charges for knowingly selling knockoffs as originals .
- The referenced buyer ( from Serbia ) isn't likely going to get "Interpol" too interested in his case ( unfortunately ) .

Perhaps you could post some pics of your 2404s ( as well as their weights ) so that others can help you make a determination .

<> cheers

[deafbykhorns]

They look like the real deal to me except for the diaphragms

http://i174.photobucket.com/albums/w90/reelmagic/IMG_0028.jpg
http://i174.photobucket.com/albums/w90/reelmagic/IMG_0027.jpg
http://i174.photobucket.com/albums/w90/reelmagic/IMG_0026.jpg
http://i174.photobucket.com/albums/w90/reelmagic/IMG_0025.jpg

[1audiohack]

Those look like real 2404's to me.

Looks like a 2405 diaphragm (by dimensions) with a 1.600" base diameter phase plug, the combination which in my experience gives the best frequency extension.

All bets are off with those diaphragms however.

[scott fitlin]

It is the aftermarket diaphragm. I know those numbers, matter of fact I pulled an aftermarket fram I have out, to look at it, and mine says 31.09 8ohm, same size gold ring. Your 2404 cores are real JBL, get real JBL frams, you should be good to go!

I have two aftermarket frams, I bought a while back, because at that moment I couldn't get a real JBL, and after I tried it, took it out and waited and spent for the real parts!

IT IS WHAT IT IS!

[ratitifb]

It is the aftermarket diaphragm...IT IS WHAT IT IS!:yes:

[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!:D
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.


:blink:

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. :D 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 diaphragmsI 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! :D

[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!

[pocketchange]

If you are looking for OEM replacements...
Check Ebay
2404H OEM JBL Diaphragm
$36.00 per w/free shipping from TX.
21 available (i got my 2) :bouncy:

[deafbykhorns]

I don't think those are OEM, they look like the ones I just replaced.
Your not from Hereford, Texas? :hmm:

[pocketchange]

I can't tell you till I get them but the question was asked if they are JBL OEM and the seller confirmed they were, his return policy and rating are good... nope, I'm in Houston.
time will tell.

[JeffW]

I don't think they are, either. The "8 Ohm" and "+" markings are clues. The JBL diaphragm only has a black dot near the - lead out, and as pointed out earlier in the thread, there are no "8 ohm" or "16 ohm" versions of the diaphragm. They all have the same DCR.

[mech986]

If you are looking for OEM replacements...
Check Ebay
2404H OEM JBL Diaphragm
$36.00 per w/free shipping from TX.
21 available (i got my 2) :bouncy:

It is very UNLIKELY that those are genuine JBL diaphragms. Rather, they are probably aftermarket units.

Here is the likely link: http://cgi.ebay.com/Diaphragm-jbl-2404-H-2404H-baby-cheek-tweeter-JBL-/280523322508?pt=LH_DefaultDomain_0&hash=item41507e348c

The seller says they are a genuine JBL Part. BS! Look at the picture of the part he is selling. Comes in a clamshell plastic case. Marked with a black on red + sticker and a date code 25.07 printed on it. Nowhere is the true OEM JBL part number or the styrofoam 2 piece shipping container that JBL ships all their vintage ring radiator diaphragms with. Now check out these other diaphragm pages:

http://cgi.ebay.com/Diaphragm-JBL-2404-2405-and-Peavey-HT94-8-ohm-/330434690486?pt=LH_DefaultDomain_0&hash=item4cef713db6

Look familiar? This guy says straight out "Aftermarket diaphragm" and the pic shows the same markings as above. Cheaper to boot until you factor in shipping, then the same. If that's true, how much are they buying them for to get profit, maybe $5?

Similar pic here too:
http://cgi.ebay.com/Diaphragm-JBL-077-2404-2404H-2405-2405H-Driver-/380270244501?pt=LH_DefaultDomain_0&hash=item5889df7295

Will be interested to hear of your experience with your new diaphragms against your hopefully intact previous JBL diaphragms. In the instance of JBL drivers, you get what you pay for.

Bart

[JeffW]

I don't think those are OEM, they look like the ones I just replaced.
Your not from Hereford, Texas? :hmm:


And that's another strange thing. Hereford is a really small little town, out in the middle of nowhere. But I see there is an authorized facility in Amarillo (http://www.jblproservice.com/service/texas.html), I was unaware of that.