Author Topic: Speaker voil coil rub/buzz?  (Read 1676 times)

lars

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Speaker voil coil rub/buzz?
« on: December 06, 2014, 07:22:14 PM »
Anyone else ever have a problem with this? I have a fairly new 12" Eminence RedCoat Governor that has developed a faint "buzzing sound", especially on bass notes. I've tried it on different amps and in free air, and the buzz is always there. The speaker is definitely the source. The coil still measures out fine on my meter, and I can't feel any coil rub when I move the cone up and down manually. I don't think the frame could have been bent in any way. I've never dropped it, and there's no visible signs of damage or warping anywhere. Could some debris have somehow made it's way into the voice coil gap, even though it's not a vented speaker? It would stink to have to trash this thing.
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morganp

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Re: Speaker voil coil rub/buzz?
« Reply #1 on: December 06, 2014, 10:16:35 PM »
One thing to check (fairly) easily before trashing it, is to look in the through the basket at the spot where the cone joins the spider, and see if there is anything stuck in there.  The probability is slim, but sometimes something like a staple or a paperclip can get attracted to the magnet and end up rattling against the spider.  Again, it's rare, but it's easy to fix if that's the case.

lars

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Re: Speaker voil coil rub/buzz?
« Reply #2 on: December 07, 2014, 11:10:42 PM »
That is an outstanding suggestion! I wouldn't be surprised if I find a metal clipping from a pcb hanging around in spider. I think a rare earth magnet could overpower the speaker magnet and pull any loose stuff out of the valleys.
Thanks.
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morganp

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Re: Speaker voil coil rub/buzz?
« Reply #3 on: December 08, 2014, 01:45:50 AM »
Before you do that, I'd suggest looking in there with a mirror and flashlight; that stuff (cone & spider) is pretty fragile and I'd hate for either to be the only things keeping some powerful magnets apart. 

lars

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Re: Speaker voil coil rub/buzz?
« Reply #4 on: December 09, 2014, 05:26:44 PM »
Well, I checked all over for any loose pieces of metal or debris in the spider...nothing. I tried it out again and listened really carefully. The buzzing sound is definitely from inside the speaker, like there's something rattling around in the voice coil gap. So the next step sounds crazy, and way more invasive, but it makes sense:

"Lay the speaker on its back with the cone facing up and with a scalpel, carefully cut out the dustcap, leaving about 1/16" of dustcap where it is glued to the cone. This is important because the voice coil wires pass through this point and you want to make sure you don't cut them. Next, use a vacuum cleaner or clean, dry pressurized air to suck or blow the dust and other debris out of the gap. If you hold the speaker upside down with the cone facing downward it will probably help getting the dust and debris out. Next, take a 3x5 index card and cut it into a strip that is the correct length so that you can form it into a circle and stick it down into the gap between the inside of the voice coil and the outside of the pole. This will help form the voice coil back into a circle. Next, lay the speaker back down on its back. Take a Q-tip or small paint brush and dip it into a bottle of acetone. Spread a small amount of this acetone on a couple of the rings of the spider, which is the brownish/yellow corrugated disk attached to the backside of the cone at the base of the basket. Next, place a jar lid or other disk on the cone where the dustcap was and let the speaker set overnight. The lid or disk will prevent dust from getting into the gap overnight, and the acetone causes the spider to relax and reposition slightly, thus repositioning the voice coil."
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wgc

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Re: Speaker voil coil rub/buzz?
« Reply #5 on: December 09, 2014, 05:45:27 PM »
You should contact the manufacturer first. Sometimes they have issues, bad glue, debris, etc and a few sneak out into the field. Nothing to lose.
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lars

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Re: Speaker voil coil rub/buzz?
« Reply #6 on: December 09, 2014, 05:58:41 PM »
I guess the basket somehow got a tiny bit bent, or the cone was glued in slightly out of alignment from the factory. Maybe it's been like that all along and nobody noticed, because it still sounds great for 90% of the notes you play, except on random low notes with the bass level up. You would never hear it under normal playing conditions, certainly not in a noisy practice room environment. I've already got the dust cap off, didn't damage anything doing that (whew) and slipped a 3x5 card in there. It's amazing how tight their tolerances are on these gaps (no wonder a tiny bit out of alignment would cause buzzing). I'll use the acetone method on the spider and let it sit overnight. We'll see if it centers things back up :o
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lars

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Re: Speaker voil coil rub/buzz?
« Reply #7 on: December 10, 2014, 11:00:40 AM »
Well, that whole process was a no-go. It's definitely a bent basket. I can put pressure on various parts of the outer rim to make the buzzing better or worse. It seems odd that this basket could bend so easily from normal use/installation. Guess it's a lesson to be learned: don't buy speakers that have massive magnet structures unless they have a cast aluminum frame. Pressed steel frames are just too flimsy. I think the weight of the back end of speaker itself put the frame out of round; it's a lot heavier than other 12s.
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cooder

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Re: Speaker voil coil rub/buzz?
« Reply #8 on: December 10, 2014, 11:43:42 AM »
If it's the weight of magnet that bent the frame out of alignement maybe you can use that to bring it back into alignement again by mounting it 180 degree reversed, gravity taking the weight the opposite way than before?!?
If you mount it that way maybe you find the coil rub disapears?
At least a very non invasive try...
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lars

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Re: Speaker voil coil rub/buzz?
« Reply #9 on: December 13, 2014, 05:36:34 PM »
Mystery finally solved, and I'm not too happy about it. I noticed the buzzing sound seemed to be louder from behind the speaker around the spider, so I really inspected it closely. I noticed one edge looked a little loose, so I tried to pry it up a little with a small flathead. The spider immediately started to pop off the basket! The glue they used to attach it to the basket is extremely weak and brittle. I was able to separate the spider cleanly off the basket all the way around without creating any damage to it. It's like it was tacked on with sticky note adhesive >:(. (power handling was probably 2 watts in that condition) No wonder the voice coil got out of alignment! Hopefully the cone is attached with the same weak stuff, and I can just reset the whole assembly like a recone project. If only I hadn't cut the dust cap, I might have been able to get a warranty replacement because this is definitely a manufacturer defect, not abuse. Oh, well.
Anybody know a good adhesive for attaching voice coil spiders, so it stays in place permanently?
The #1 personal survival tool you need to save your family? A tactical flashlight of course! (not things like water or food or clothing).