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View Full Version : Diaphragms: better new or replaced? Why?



eziodoc
11-04-2008, 04:20 PM
Hello friends,

I hope my questions are clear (english isn't my native language), also if aren't questions from a professional: sorry for this..

About the diaphragms question:

1 - How I can to recognize if a component (driver, supertw) has a replaced diaphragm or the original one?
The component is sealed and after diaphragm replacing is clear the work made on it?
2 - In your opinion is better a driver or supertw with original diaphragm or with replaced one (also if original)?
3 - Why I see always the JBL monitors sold (also on bay, last the 4350 Germany, described on marketplace), described happily from seller "having original diaphragms", with great satisfaction? The original ones are really always better, if not damaged?

Thanks for answer my questions, my old doubts..
Ezio

ratitifb
11-05-2008, 12:54 AM
by taking appart the aluminium/titanium debate, a new JBL original (not aftermarket) dia is better regarding fatigue if pro and well mounted :)

Mr. Widget
11-05-2008, 08:45 AM
1 - How I can to recognize if a component (driver, supertw) has a replaced diaphragm or the original one?It varies from driver to driver. In some cases it is very difficult to know for sure.


2 - In your opinion is better a driver or supertw with original diaphragm or with replaced one (also if original)?Most of the vintage drivers that I have tested are no longer in spec. I always prefer to buy drivers with blown diaphragms and replace them with new factory fresh diaphragms from JBL. Even if the drivers are mint looking with original diaphragms, it is rare that they perform as new.


3 - Why I see always the JBL monitors sold (also on bay, last the 4350 Germany, described on marketplace), described happily from seller "having original diaphragms", with great satisfaction? The original ones are really always better, if not damaged?If you are talking about a vintage museum piece where acoustic performance is secondary, then an original diaphragm makes sense, but if you are interested in a high performance audio system then you may not want an original diaphragm.

Widget

scott fitlin
11-05-2008, 09:55 AM
Recording studios seem to feel diaphragms change over time, and not for the better.

Lots of TOP studios used to change the diaphragms every two years.

Allanvh5150
11-06-2008, 01:17 AM
I have found that if they are not overdriven diaphragms will remain very good for a very long period. But knowing if they have been driven correctly is the trick.

scott fitlin
11-06-2008, 04:45 AM
Interesting point. A woofer shows its use, soft or sagging suspension, etc.

But how do you tell with a compression driver diaphragm?

eziodoc
11-06-2008, 02:06 PM
by taking appart the aluminium/titanium debate, a new JBL original (not aftermarket) dia is better regarding fatigue if pro and well mounted :)


It varies from driver to driver. In some cases it is very difficult to know for sure.

Most of the vintage drivers that I have tested are no longer in spec. I always prefer to buy drivers with blown diaphragms and replace them with new factory fresh diaphragms from JBL. Even if the drivers are mint looking with original diaphragms, it is rare that they perform as new.

If you are talking about a vintage museum piece where acoustic performance is secondary, then an original diaphragm makes sense, but if you are interested in a high performance audio system then you may not want an original diaphragm.

Widget
Hi Mr Widget,

thanks for clear answers and thanks also to all: the problem is clear', isn't easy to confirm if a diaphragm needs to be replaced or if it works yet fine..
Last question: a component unit come from factory "sealed"? Or better, if I open a component and I replace the old diaphragm with a new one, an other guy can to recognize the component was opened? A component is really "sealed" and after this replacing operation appears clearly to be a no longer "sealed" component?

Sorry for for questions, for you surely idiot, for me new things..

Thank you.
Ezio

mvaldes
11-06-2008, 09:54 PM
If you can run a frequency response test and compare it with a new driver or diaphragm, you can see if it is “on spec” or not.
But you need some testing equipment.

Michele

Mr. Widget
11-06-2008, 11:51 PM
I have found that if they are not overdriven diaphragms will remain very good for a very long period. But knowing if they have been driven correctly is the trick.My experience is anecdotal at best. I have measured a dozen or so used drivers purchased from eBay. These drivers were used in wide ranging applications. Virtually none of them measured anywhere near the specified response that JBL publishes. Virtually every new driver I have measured has exceeded the publish specifications and fully charged used drivers will meet or exceed original specs with new diaphragms... usually.



Last question: a component unit come from factory "sealed"? Or better, if I open a component and I replace the old diaphragm with a new one, an other guy can to recognize the component was opened? It depends on the driver. Most older JBLs did have some sort of seal. For some it was a wax seal. For others it was a drop of paint... and others it was the foilcal. In all cases an unscrupulous seller could hide the fact that the driver was opened to varying levels of success. In most cases the new JBL diaphragms are obviously different that the old original ones. A knowledgeable inspector will know if the diaphragm is correct.


Widget

Allanvh5150
11-07-2008, 02:07 AM
The only way that I consider actually knowing what the driver has been up to all it's life is if I actually own it and have been kind to it. Second hand, who would have a clue. Throw a new Phragm at it to be sure. :)

mvaldes
11-07-2008, 02:21 AM
Virtually every new driver I have measured has exceeded the publish specifications and fully charged used drivers will meet or exceed original specs with new diaphragms... usually.

Widget


Widget,
when you measure a driver, and found some discrepancy with factory spec for that driver, how can you understand if the driver is not fully chargeed or if it's a diaphragm problem ?
I don't have a gaussmeter and I've have a pair of 2421 that want to check.....


Michele

Mr. Widget
11-07-2008, 07:17 AM
Widget,
when you measure a driver, and found some discrepancy with factory spec for that driver, how can you understand if the driver is not fully chargeed or if it's a diaphragm problem ?
I don't have a gaussmeter and I've have a pair of 2421 that want to check.....You need proper test equipment to know for sure. Without it and the knowledge of how to use the test equipment, your best bet is to have the driver recharged and a new diaphragm put in it... recharging is cheap, diaphragms are not, but without going through these steps, you really have no idea what you've got.

We are talking about compression drivers here, but vintage woofers also need to be charged and re-coned. All loudspeakers start out too stiff, they break-in after several hours of play and then eventually after many years of play they break down.


Widget

Robh3606
11-07-2008, 09:25 AM
your best bet is to have the driver recharged and a new diaphragm put in it... recharging is cheap, diaphragms are not, but without going through these steps, you really have no idea what you've got.


Well maybe it's me but I wouldn't have any Alnico compression drivers, underhung Alnico's woofers, or any other driver that fit's into the description Greg uses in his post remaged. If you read Gregs post these driver types should not need to be recharged. They will not loose gap strength due to driver. If you decide to have them recharged the guys doing it should be up front about how they are going to verify that the job is done correctly and you end up with the correct gap flux.

http://www.audioheritage.org/vbulletin/showthread.php?p=177175#post177175


Rob:)

mvaldes
11-07-2008, 10:45 AM
You need proper test equipment to know for sure. Without it and the knowledge of how to use the test equipment, your best bet is to have the driver recharged and a new diaphragm put in it... recharging is cheap, diaphragms are not, but without going through these steps, you really have no idea what you've got.

We are talking about compression drivers here, but vintage woofers also need to be charged and re-coned. All loudspeakers start out too stiff, they break-in after several hours of play and then eventually after many years of play they break down.


Widget

Thank you very much for your answer.
I normally make my measurement with Clio, and thought that having a close look to some data, can give a clue on the mag condition.
So, the question could be:
which are the figures that change on a alnico degaussed compression driver (or woofer) ?

Michele

Robh3606
11-07-2008, 12:06 PM
which are the figures that change on a alnico degaussed compression driver (or woofer) ?

BL and reduced sensitivity as well as reduced high frequency response. You should be able to model the effects in a box program.

Rob:)

coherent_guy
11-07-2008, 12:20 PM
Sure would of been helpful if JBL had put their logo on the diaphragms, or their part number. Not always possible of course, but on compression driver diaphragms, the plastic mounting ring sure could have something put on it. I don't have much experience with JBL compression drivers and their diaphragms, having only pairs of 2420s, 2425s, 2402s and 2405s. I think the 2402 had a number on the edge of the diaphragm, and I think my 2420s (labeled LE85) were redone, they are missing the wax seals, and I've never opened the 2425. So JBL never marked their compression driver diaphragms at all? Seems kinda odd... :blink:

Allanvh5150
11-07-2008, 12:43 PM
It would be far to easy for a JBL logo to appear on the diaphragms. I have never seen an ID on the cone kits either.:)