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In Reply to: RE: Mechanical buzz in JBL D123-question for speaker repair gurus posted by mac55 on June 06, 2017 at 08:06:25
Hi, didn't have time to check all replies, but first check for
a broken glue joint on dust cap...those can buzz at certain frequencies.
Well just remove it and check for buzz again. If buzz gone, re-glue cap
If buzz still present, you can inspect the cone/bobbin joint. Those are
known to come loose...use epoxy. Also look for any contact of
the bobbin on the pole piece while moving the cone. Check for
Next is the spider to cone glue joint. Those can come loose and buzz or click. Epoxy is best here.
Let me know results...
I tried holding the surround at virtually all points from underneath and above, but nothing changed the buzz. I also tried what I thought was a novel idea of using masking tape applied to the cone to pull on it in various ways while listening for a change in the buzz. Nothing changed it. Visually, everything looks dead mint, and no rub is remotely detectable. I also made a slim tool out of wire to press on the internal grill in case it was buzzing, to no avail.
With respect to removing the dustcap, I watched a youtube video of a tech sliding an exacto knife around the cap. Here's my question. Is there a flange or lip to these dust caps, or are they literally a section of a sphere with a sharp edge?
And I'm sure I'll catch heck for not disclosing the whole story, but I actually have two D123's, and they both exhibit the same buzz. Now I'm sure the first thing everyone will think is that it has to be something other than the speakers, and that's part of the reason why I didn't complicate things by mentioning it at the outset, but the speakers buzz with multiple amps and multiple guitars, and my other speakers, of which I have many, do not buzz with those same amps and guitars.
You just cut the cap at the very outer edge ...maybe 1mm
away from the crease. You don't need the lip to glue it back
on. Set it on the cone, then run the bead of glue around it.
I don't think it's a surround problem, but one of the three
The mystery deepens. I dug out an HP signal generator (yes, I realize I should have done this much earlier) and connected it to my amp and one of the speakers. No remote buzz anywhere in the audible spectrum, even at moderate power. However, very oddly, there is a resonance at 120 Hz. In other words, if I sweep just north or south of 120, I can hear beats, which increase in tempo as I sweep north or south. It's not at all like it manifests as buzz when playing, but I cannot account for it. And it's present in both speakers! Any thoughts?
Update: I just tried running the amplifier and the HP signal generator on a Oneac power conditioner I run my stereo through, and the resonance is still there.
Update #2: I just tried another speaker, a 12" alnico Marsland, and I can detect beats around 120 Hz, perhaps to a slightly lesser degree, but they're there.
Update #3: I just realized that it's plausible the 120 Hz (60) resonance is coming directly from the power supply of HP tone generator, which is at least 40 year old.
Yep, bad 40 yr. old filter caps in pwr. supply.
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