Help with changing hf diaphragms / cleaning gap

Hi all, looking for some advice.
I'm replacing the diaphragms on my jbl mp415s with bms 4540s as they are a direct replacement.

Just been cleaning the magnetic gap with a business card and masking tape.

If I go as deep as the voice coil does or a bit deeper it is clean. However if I push as deep as I can there seems to be a seemingly endless supply of non magnetic material.
It appears to be bits of black acoustic foam?!

Not sure what to do... At the depth the vc sits it's clean but I don't know what or why this stuff is?!

Tempted to blow the gap out with compressed air...
What do you all think?

Cheers

I'd advise against using compressed air. It will just blow anything sticky further into the magnet assembly and make it harder to remove.

The best way is to use a vacuum cleaner. This works best if you make a reducing nozzle for the end of the hose. You can do this with heatshrink tubing, just keep adding layers until it's stiff enough to avoid collapsing from the suction. I find about half an inch diameter (when shrunk) works well. Repeatedly running it around the gap will pull out a lot of the crap, before cleaning with the usual the sticky tape and card.

I wonder if your driver had a layer of foam over a rear air vent, that has disintegrated over the years?


Edited by madboffin - 17 August 2017 at 5:50pm

madboffin wrote: I'd advise against using compressed air. It will just blow anything sticky further into the magnet assembly and make it harder to remove. The best way is to use a vacuum cleaner. This works best if you make a reducing nozzle for the end of the hose. You can do this with heatshrink tubing, just keep adding layers until it's stiff enough to avoid collapsing from the suction. I find about half an inch diameter (when shrunk) works well. Repeatedly running it around the gap will pull out a lot of the crap, before cleaning with the usual the sticky tape and card. I wonder if your driver had a layer of foam over a rear air vent, that has disintegrated over the years?

Ah ofcourse, don't know why I didn't think of that ... Damn... I went nuts on it with 8 bar of compressed air but kept going in a circle to coax it out. A fair few bits did fly out including some big enough to need teasing out with a bit of card.

They're jbl2406s fitted with bms 4540 diaphragms and they sound amazing.
If one of these bits of foam gets into the gap and interferes with the voice coil what's likely to happen?

Cheers