MusicMan 4x12GS EVM 12L speaker trouble

[torpethin]

Hello! this is my first post to the forum, nice to meet ya'll.

I recently acquired a Music Man HD 150 with matching 4x12 Gs guitar cabinet. I'm really happy with it so far, with one exception, which is a speaker problem.

The cabinet contains 4 12" EVM 12L II speakers. They sound incredible with the high watt Music Man; they're loud and clear with a great range and response. This is a sealed cabinet made out of a heavy wood, and the addition of 4 20 pound speakers makes this a heavy cabinet indeed. But its worth it, since it sounds so good.

The problem:
t
he top left speaker makes a funny noise. I noticed this when I bought it, and was able to talk the seller down. The sound is mild distortion, more reactive to lower frequencies. No flapping sound like its blown, just a distortion that comes from this one speaker. I probably wouldn't have noticed it if this amp and all the speakers didn't produce such a clean signal.

Oddly, this speaker has no visible damage and all the wiring looks good.

I'm stumped. I know these speakers are known for their reliability and the fact that the speaker is in great visible condition makes it hard to understand what could be wrong.

If anyone has some insight, I'd be delighted. Trying to figure this out on my own before I take it in to a pro.

[Jazz P Bass]

Sounds like the speaker in question is exhibiting "coil rub".
The coil is rubbing on the former.
You could try flipping the speaker 180 degrees.

[torpethin]

Did a bit of reading on it, and this is indeed voice coil rubbing.

Thanks for the helpful diagnosis, at least I know what's wrong. It actually rubs pretty badly, so I'm not sure that rotating it will work. I'm going to leave it overnight and hopefully gravity will help me out.

Other options include reconing the speaker, which will not be cheap. Weber does reconing for EVM @ $95, but these damn things weight 20 lbs, so shipping will be a nightmare. I'll search locally.

Anyone have experience with the reconing kits? Not sure that I trust myself do it, unless others can verify that it's as easy as advertised.

[jrfrond]

Voice coil rub is caused by one of two things: overheating and blistering of the voice coil (kind of unlikely in your case), and gravity. Specifically, when a speaker sits in one position, over time, the spider and cone sag downward, particularly in speakers with heavy voice coils like the EV's, which are wound on an aluminum former. This is heavier than the more common Kapton.

I've never tried it, but you can turn the speaker 180 degrees and hope the problem EVENTUALLY straightens itself out by sagging the OTHER way, but the REAL fix is a recone. In addition to the speaker parts being fatigued, voice coil rub can change the impedance of a voice coil because adjacent windings can short out.

[J M Fahey]

Before reconing you can try a cure or kill medicine.
*Very* carefully cut the speaker dome around, with a new very sharp box cutter, all around where it's glued to the cone or voice coil.
The idea is that you stay always slightly over 1mm away from the voice coil or cone, so you do not damage them, only cut the dome/dust cover.
You will see the voice coil and the metallic center pole.
Fashion a strip about 1" wide by 4 or 5" long out of old X-Ray film or similar material a, slip it between voice coil forner and center pole and move it around sweeping the very thin gap between them.
It should move freely full circle in a good speaker; yours will find a tighter spot where it will be difficult to move (if the VC sagged as suggested) or you will clearly feel a "bubble" or feel something scratchy (dust).
Move it back and forth in the problematic area, make sweeping movements towards the outside (you might have dust, sand or some minuscule metal scrap there)
You have a great possibility of repairing the problem.
If clearly sagged to one side, insert a double or triple thickness of film i the narrow side, so you force it towards the other side.
Later, pulling the strips, it should work in most cases.
You can carefully reglue the cut dome with some silicone sealant or a ring of contact cement, which can be reinforced 1 day later.
Do not use rigid adhesives as epoxy or crazy glue/cyanoacrilate, because they crack or unglue in the furure and buzz horribly.
Good luck.

[Jazz P Bass]

Purty slick J.M.
I have seen all sorts of stuff in the coil.
My favorite is when the filter on the magnet deteriorates & gets in there.