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Voice coil rub


BottomEndian
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Just a quick question... er... what it says in the title. Rehearsal last night, guitarist's rig starts making nasty scratchy noises from two of the speakers in his 4x12. Sounds OK when played [b]very[/b] quietly, but if he hits a note with mid-to-high vigour, the noise is there. It's very reminiscent of a dodgy lead (scritchy, scratchy, sputtery, crackly distortion), and we've narrowed it down (via swapping leads, heads, everything) to just the cab, and the top two 12s in particular.

Sound like voice coil rub? Bear in mind he tunes down to drop-G, uses heavy fuzz and these are speakers voiced for guitar... and you'll see why I suspect the coils may have given up the ghost. :) Lots of energy ploughing through those poor little things.

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[quote name='wateroftyne' post='1176988' date='Mar 26 2011, 10:22 AM']Turn the cab on its side / upside down and see if it still does it...[/quote]
Yeah, I think that might be the next course of action. It only started playing up towards the end of the session, so we didn't have much time for muckin' aboot.

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[quote name='BottomEndian' post='1176991' date='Mar 26 2011, 10:24 AM']Yeah, I think that might be the next course of action. It only started playing up towards the end of the session, so we didn't have much time for muckin' aboot.[/quote]

Hi Owain

Sounds like they are gonners. They voice coils start to drag when they get over hot, they may stop when they have cooled but it is unlikely, It usually sounds as you have described barky, scratchy etc, which is the expanded coil catching the sides of the magnet on its travel.

If you want to test the damage, place the cab on its back and push the coils gently by hand and if you can feel it catching then its buggered. :)

If you cant move it at all then it has welded itself to the magnet, This has happened to me before when i lent my monitors to an ex student for PA hire, how he manged to blow 2, 15 inch monitors capable of handling 500 watts each and not realise at the Head of Steam is beyond me :)

Tell Tim, Phil Poolan at work has an old pair of Burman 12s which he has no use for.

Cheers

Dave

Edited by cd_david
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[quote name='BottomEndian' post='1177126' date='Mar 26 2011, 12:29 PM']Cheers Dave! Do you know the impedance of the Burmans, by any chance?

Ta for the PM too... I'll have a chat to Tim, but I'm about to be away for a few days.[/quote]

No hurry mate, let me know as and when, I will ask Phil monday but at a guess 8 ohms at 50 watts

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Hi there. I am said guitarist with the scratchy speakers.

I will try out the suggestions made - thanks.

Hi Dave. Cheers for the offer on the Burmans. Really I would need some 16 ohms so I can wire the cab to 4 ohms. The speakers I have in the cab are all Eminence Tonkers. Given that two have most likely gone forever, I suspect it's only a matter of time before the other two go. Owain and I briefly discussed fitting some bass 12s. We'll see :)

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