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In Reply to: RE: Mechanical buzz in JBL D123-question for speaker repair gurus posted by airtime on June 07, 2017 at 08:19:06
I just removed perhaps 5 or 6 small pieces of particle board from the surround using tweezers, right down close to the frame, although I won't have time to test it until later. The largest was a good 3/32" across, so I'm hoping that was the problem. Will report back later.
That COULD do it - let's hope!!!
After one pass of removing debris, I was confident I heard an improvement, but could still detect some buzz. This was with the speaker out and sitting on its back for testing. I then did another pass of debris clearing and found perhaps another 6 smaller pieces, but again, right up near where the surround meets the frame. It's a very awkward place to get to and I needed a small flashlight, reading glasses, a toothpick, and tweezers to do the job.
I also tried a trick I thought of based on the comment by DJK, that the cone may have sagged over the long haul and could be rubbing at the voice coil. I put a piece of thread around the cone where it meets the spider and tied a large loop. I was then able to apply some gentle force by pulling the loop in the opposite direction to how the cone would have sagged *if* it had sagged. There was no effect, so it seems unlikely that internal rubbing is the problem.
I tried again after the second debris clearing pass and felt there was a substantial improvement, perhaps even no buzz, but I couldn't be positive because I was also suffering some aural fatigue from listening so critically for every little thing at volume higher than I normally listen at. I put the speaker back in the cabinet and was disappointed to hear obvious buzz. It's a 14 x 12 x 24" speaker cabinet with the tweeter hole boarded over, a bass port, and the back open.
I then started putting pressure on the cabinet sides, and other places while playing (using a looper pedal to generate signal for hands free testing) but when I pulled on the bass port, the buzz kicked up considerably, and could be controlled depending on how I applied pressure to it. So, it seems as though I had compound issues. Now I have to solve the cabinet. What's interesting and new to me is that the buzz from the debris in the surround (the speaker buzzed even when it was apart from the cabinet, so it was definitely a good part of the problem) is remarkably similar to the buzz now coming from the cabinet, to the point one could easily confuse them. My lesson learned is mechanical buzzes can manifest anywhere and sound similar regardless of where they come from. I'll report back once I've had a chance to address the cabinet with some glue, screws, or what have you.
I'm completely stumped. I thought I had solved it, but it's still there, even with the speaker out of the cabinet. I've tried moving the tinsel. I've tried different guitars and different amps. I've tried pressing on the surround on every inch, but nothing works. My new guess is something loose under the dust cap.
I'm sure I'm going to get warnings not to proceed this way, but how would one go about removing the dust caps? Is there a solvent to soften the glue joint? Any good books to recommend on speaker servicing?
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