4344MKII and 275ND problem
Hello,
I am a happy owner of a pair of JBL 4344MKII ... but I have a big problem : the level of one of the 275ND compression drivers is 6 dB under the normal level. Of course, I reversed the two 275ND to be shure that it was not a filter problem. Then I changed the diaphram with a new one and the problem remains. So it seems obvious that it is a compression driver problem, perhaps a magnet problem ?
My préamp is a TACT RCS2.2x and the amps are TACT 2150. As the preamp is a room correction préamp, it succeeds in giving a flat response curve by applying corrections and amplifying the frequencies between 1.3 and 8 kHz.
I mailed to Harman USA but never got an answer and Harman France told me that is was not possible to re magnetize the magnets of a 275ND.
Have you ever heard of such speakers problems ?
Excuse my very poor english and thank you for your help.
Pascal
Re: 4344MKII and 275ND problem
Quote:
Originally posted by spirou38
... Of course, I reversed the two 275ND to be shure that it was not a filter problem. Then I changed the diaphram with a new one and the problem remains. So it seems obvious that it is a compression driver problem, perhaps a magnet problem ?...
Pascal
Pascal,
Just try the following:
Test the new diaphragm in the good 275ND as you may have a new defective diaphragm.
If the diaphragm is fine, try the bad one in place of the good one.
Thus will let you know who is responsible!
Bonjour,
Voici une méthode d'investigation:
Placer ne nouveau diaphragme dans le bon moteur pour vérifier un éventuel défaut du diaphragme neuf.
Placer le "mauvais" diaphragme dan le moteur qui est bon pour déterminer si c'est un problème de diaphragme ou d'aimant!
Neodymium can be re magnetized
Hi Pascal
If you find out that the magnet in the bad driver is weaker than that of the good ones
( you have to get it confirmed by a serious measurement at some factory or university or at the JBL/Harman-France) then you can have the 275ND re magnetized
The only thing is that Neodymium is much harder to re magnetiz than other magnetic materials (eg. Alnico, Cobolt, Ferrite etc), and one must use a lot more of
power/energy to magnetize ND-materials. Because of that there is not all of the magnetizing factories that have the necessarily equipment to do such a work.
Hope its not a magnetic problem with your 275ND-driver.
How old are these drivers ?
Best Regards
4344MKII and 275ND problem
Hi Yuri,
Here is what I did :
- I reversed the two 275ND in the 4344MKII -> the probem that was on the left channel is transfered to the right channel ;
- I tried the new diaphragm in the good 275ND ( to be sure that it was a good diaphragm ) -> OK ;
- I tried the old diaphragm that I suspected in the good 275ND -> also OK ;
- I tried the new diaphragm in the bad 275ND -> more than 6 dB under the normal level :confused: ;
So I'm sure that the problem comes from the driver, not from the diaphragm ; I'm also sure that the diaphram is correctly centered. It's why I suspect the magnets. Do you think it is possible to re magnetize the neodynium magnets ? Or where could the problem come from ?
Pascal