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retro soulman
09-24-2017, 07:20 AM
Hello! I recently purchased a pair of 2405, i check visual the diaphragms and the dcr of each driver. The dcr in both diaphragm was the same and the diaphragms visual looks
In ok condition. After taking them home i hooked them on my system and i realize that the one plays lower than the other and also with less detail. The diaphragms looks original and the one driver with the issue looks like never been opened before. Whats the problem could be?
7842678427

bldozier
09-24-2017, 09:26 AM
polarity maybe

retro soulman
09-24-2017, 09:50 AM
polarity maybe
What has to do with polarity?

1audiohack
09-24-2017, 10:57 AM
Hi Soulman!

I have seen this a couple of times and found the diapragm not quite centered and or being preloaded (pushed or being slightly distorted) by the bullet or the outer horn.

When you get them free from coil contact with a surface in the gap and external forces they come alive.

I don't know what you have for test equipment but one can usually see this with a high resolution impedance test where the motional impedance peak will be abnormally low if there is any coil to motor contact. Note that these don't have enough excursion to sound broken if there is coil contact, they just sound weak.

On the other hand if the coil is separating or the diaphragm is broken the impedance peak will be very high.

In the absence of test equipment, swap diaphragms in the drivers and see if the issue follows the motor or diaphragm. Usually careful re-assembly is the fix.

Off subject, my family is in your beautiful country and loving every minute of it. :)

All the best,,
Barry.

RMC
09-24-2017, 11:18 AM
Hi Soulman,

Diagnostic based on a picture is always an adventure... That being said, IF we disregard faulty connection (e.g. intermittent) and polarity, then the following MAY be issues seen on the second picture presumably the problematic one (dated 6-30-89) since you didn't say.

These are guesses. Comparing both pictures, on the top one there is a "R" which suggests repaired or replaced? On the bottom picture, the small yellow ring appears to show a larger space (top left) than the other tweeter could that mean "off center"? Also the diaphragm appears to show some dent or bump (bottom left) as well as something on the right hand side. Could these explain the output level difference? I don't know.

I did have a similar level problem many years ago with an "original" Motorola piezo tweeter. When I opened it and compared it to other real originals I have, I realized the one with the level issue had a noticeably smaller diaphragm than the real originals. That meant this particular unit, I had purchased used, had been repaired with other than original part even though it did say Motorola on the tweeter... But that story doesn't APPEAR to be your case here. Regards,

Richard

retro soulman
09-24-2017, 12:25 PM
The problematic one is the bottom one!

retro soulman
09-24-2017, 12:29 PM
So maybe the best is to remove the diaphragm and maybe clean also the vc gap

1audiohack
09-24-2017, 12:53 PM
I brlieve a physical inspection is in order.

Barry.

Tim Rinkerman
09-24-2017, 01:15 PM
Judging by the marks in the aluminum...these diaphragms have been somewhat...abused.

christo
09-24-2017, 02:00 PM
Judging by the marks in the aluminum...these diaphragms have been somewhat...abused.

I would agree, I had the same issue - low output and there was a dent in the diaphram

RMC
09-24-2017, 04:54 PM
Hi Soulman,

Well I'm glad and old man's guesses , like me, in post # 5, weren't that off the track, even though I don't own nor have opened any 2405... Reading Barry's post re "off center" and Christo's and Tim's posts re "dent" tells me close observation and logic can go some way re diagnostic.

That certainly doesn't make me yet a sage man nor a smarter guy, but I sure am working on it. Regards,

Richard

bldozier
09-24-2017, 05:07 PM
Honestly I was mentioning your connections
but, maybe it's the diaphragm
ok bye.

retro soulman
09-24-2017, 06:09 PM
Also the "good one" has worst dents but it plays great! Also it doesn't look off centered. Im a little afraid to remove the diaphragm to be honest.

RMC
09-24-2017, 08:00 PM
Hi Soulman,

Worst LOOKING dents don't mean automatically more damaging. Those of the weak unit may impair the tweeter more than the bad LOOKING ones. Not much else you can do but to follow Barry's advice in post # 4. Unless he has more tricks up his sleeve... The guy knows 2405 details much better than I do.

Richard

1audiohack
09-25-2017, 06:22 AM
... Im a little afraid to remove the diaphragm to be honest.

I understand, that's perfectly rational. As it is though it's not performing properly so your possible losses should you ruin it are small no?

If you choose to take it apart the first real trick is in the unsoldering of the leads. These are very fragile as you can see. I use a wood tooth pick as the tool to carefully coax the lead out of the terminal loop while the solder is melted. Wood wont melt nor will anything stick to it.

After the leads are free, if the diaphragm wont lift out easily you may have to get under it with a thin sharp blade.

Jbl currently does not have any D16R2405's in stock. The due date for more is 09/30/2017.

The pictures taken from on center make it harder to tell but it looks like these are the ferrite versions?

Barry.

retro soulman
09-25-2017, 08:54 AM
Yeap they are the ferrite versions. Today i realize that both tweeters got same sound and less gain than my older ones. The old ones are a little sharper and brighter in sound. But they are also 1ohm less than the new ones!

toddalin
09-26-2017, 01:30 PM
Looking at the diaphragms, it appears that even though it may appear that no one has opened it, in fact they have.

So why is one quieter?

Possibly, (and a very real possability at that), is that when reassembled, the tech/whomever did not secure/hold the phase plug steady on reassembly as they tightened the screw. This will then allow the diaphragm to twist a bit in its mount and this will reduce the volume.

It could be that they will both sound about the same on reassembly, assuming you don't make the same mistake.

BTDT!