Jbl 375 issue

[Doctor_Electron]

I am curious. If 375's or other comp. drivers are used in a stereo configuration of two loudspeaker systems, with a 375 in each cabinet, and one is damaged magnetically should both drivers' magnetic assemblies be re-magnetized to ensure balance? Is there a type of gaussmeter that can be used to check the flux level?

regards, -D_E-

[script56]

I sent both to remag so they both came back recharged. Only $20 each.

[toddalin]

I am curious. If 375's or other comp. drivers are used in a stereo configuration of two loudspeaker systems, with a 375 in each cabinet, and one is damaged magnetically should both drivers' magnetic assemblies be re-magnetized to ensure balance? Is there a type of gaussmeter that can be used to check the flux level?

regards, -D_E-

Typically,no. They just recharge them until they are saturated and call it good.

[Mike Caldwell]

I sent to Great Plains audio for re mag. Diaphragms are factory new Jbl.

As for the new JBL diaphragms, about a month ago I went to replace a diaphragm in one of my 2426 drivers with a new JBL replacement that had been on my parts shelf for about a year. First it would not fit in the milled alignment recessed area with out getting stuck and it had a couple globs of glue on the voice coil that would rub in the gap. You could also clearly see the aluminum ring that holds the diaphragm did not get punched out cleanly leaving large burr along one side.

JBL service would have nothing to do with the diaphragm since it was out of warranty, they did not know how it had been stored and if it had been installed correctly. The guy I talked to gave me the impression he had never changed a diaphragm!

I was able to salvage the diaphragm by filing the aluminum ring smooth and oh so very carefully scraping the globs of glue off the voice with an xacto knife.

So in short, a new diaphragm these days may not be without issues.

[Flodstroem]

Is there a type of gaussmeter that can be used to check the flux level?

regards, -D_E-

Yes, for example F.W. Bell produce and have produced many models that could be used for checking the gauss-flux level. However, the probe must be the transversal type of probe, not thicker than approx 1 mm / 0.039" The gauss meter must have a scale up toat least 10 kGauss (for paper cone models) or at least 20 kGauss for most of the compression drivers.
When magnetizing an Alnico magnet as toddalin mention it have to be enough magnetized so it saturate. Any flux levels higher than that will have no effect as soon as it have ben saturated.
So its relative easy to remag Alnico (5) just zap the magnet with a magnetic pulse larger than than saturation level and all the magnets will become the same as they where when they left the factory.....
The flux level in the magnetic gap then depends on the mass of the Alnico magnet combined with the structure of the magnetic motor, pole pieces, diameter of the center pole etc etc..