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In Reply to: RE: found problem with 808-8A frequency response ... posted by deathtube 667 on March 19, 2015 at 05:55:31
Being AlNiCo drivers high SPL (read high temperature) doesn't bother them. Indeed less than any other magnetic material, AlNiCo is the only one which remains magnetic even if heated to red hot.
However AlNiCo is VERY susceptible to physical shock. They will weaken considerably if dropped or generally being thrown around in their enclosures. Unfortunately this is also common if used in a touring PA.
Follow Ups:
If you take off the top plate it will need to be remagnatized.
I removed the back cover and diaphragm so I could shine a light thru the phase plug and see if the bug screen needed cleaning.Bill at GPA suggested removing the bug screen, but I have read that it can collapse the magnetic field of the driver, so the bug screens were left alone.
I was not sure how to properly take the driver apart any further without damaging it, so that was as far as I went with the process.
There is a local prosound/MI/electronics repair depot close to home and I dropped off the drivers for their speaker tech to evaluate.One of the sales guys said they might have re-mag equipment in the shop, perhaps later today I will know if they can help or not.
Edit : the local repair depot failed to produce results, so I sent the 808's off to GPA.
Bubble wrapped and doubled boxed them to survive UPS delivery goons, but IME they can trash anything.
Edits: 03/20/15
Cutting out the bug screen won't do anything to the magnetic field unless you pull apart the entire motor assembly to get the screen out.
In one of your previous posts, you noted your 808-8A's had a weak pull on a screw driver compared to a Dayton driver. The 808's have a center Alnico ring inside a pot structure. This is very well shielded - it doesn't have a lot of stray flux outside the structure, thus weak pull for a screwdriver. The Dayton driver has a ceramic ring magnet on the outside of the magnetic system. This has tons of stray flux and thus has exerts a high force on a screwdriver held near it. In other words, that observation is completely as expected. I guess a bit late now as you already had them remagged.
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