Here's What Coil Rub Sounds Like...

cooljuk

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This early 1970s Marshall cab recently came into the shop and has speakers that range from no rub to just terrible rub. I shot a couple videos to show the differences. I wasn't sure if the phone camera was going to pick up the individual speakers well but it actually came through very obviously.

Here's what coil rub sounds like over a test signal:


Here's what it sounds like mechanically by manipulating the spider/cone:


If you could feel the speakers moving with your own hands, you'd notice that they felt just exactly like they sound. The one without rub, smooth and dampened with no resistance. The one with the terrible awful grainy sound, it feels like there's sand and gravel in the coil gap. The other, in between.
 

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Is there a fix for the rub? Like some lubrication. Or is it a permanent misalignment thing
 

cooljuk

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Is there a fix for the rub? Like some lubrication. Or is it a permanent misalignment thing
It's caused by either misalignment, crud in the gap, or both. Typically, a speaker would get reconed, with just about everything but the frame and magnet replaced.

I have a few greenback Celestions, even older than those creambacks above, that have fine Pulsonic cones but the coils are rubbing. I'm going to attempt to remove the coils and clean the gaps, then reinstall and realign the original coils. I've not yet attempted that process and it's a little intimidating. At the moment, they are useless, though., The very worst thing that can happen is I mess up the old parts and have to send the frames to Weber for reconing, which just puts me back to where I am now, anyway. At least I'll get to learn something and gain some experience, if I try.

I have been able to fix one or two easy ones that just need a little re-alignment by setting up a jig and, with strong but slow and controlled force, pushing the magnet against the frame in some particular direction opposite of whatever impact caused its misalignment. Same as would happen in auto collision repair. That's only useful on speakers with very slight rub and no crud in the gap.
 

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I watched a YouTube vid where the guy removed dust cap, cleaned the crud out, wedged a plasticised paper all round the voice coil gap so it’s held centered and then used isopropyl alcohol on the spider, just wetting it enough to loosen the fabrics glue or whatever it is that provides the rigidity of the spider , I think the idea is when it rehardens it centres itself as the paper wedges force it to align to a centred position. He did something with the driver as well, but cannot remember what exactly, cannot find the vid at mo, will post if I find it.

found it.

 
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Soul Tramp

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Another cause of this is the VC winding coming apart. You'll see this in speakers that have been pushed too hard for to long. The extreme heat generated by the abuse can cause the VC to de-bond.
 

cooljuk

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Another cause of this is the VC winding coming apart. You'll see this in speakers that have been pushed too hard for to long. The extreme heat generated by the abuse can cause the VC to de-bond.
That's intense! I didn't know that. That must take quite a bit of heat.
I've seen PA speaker coils that arced and opened or welded themselves. I guess that's from what's essentially DC voltage at the top and bottom of a severely clipped signal?
 
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ehb

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You mean a woofer AIN'T supposed to travel like the suck & blow valve on a steam locomotive?

So that's why th... Oh never mind....

:cool2:
 

ehb

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That's intense! I didn't know that. That must take quite a bit of heat.
I've seen PA speaker coils that arced and opened or welded themselves. I guess that's from what's essentially DC voltage at the top and bottom of a severely clipped signal?

Them damn duty cycles'll get ya every time....

Saw a cone in a floor catch fire once.... Waaaay too much wattage.....no crowbar.....


Decades back, worked at a musico and boss loved renting out small PA stuff on weekends.... I usually spent time first of week replacing drivers.... Kept a pile of motorola cheap ass tweeters and the little horns in the shop...
DJ mixer into a PA mixer channel into a power amp into drivers.... Rented by folks that think when they see blinking leds, everything is cool....especially them red ones... What can happen? :laugh2:

Like a damn game of which stage goes sq wave first... Don't much make a damn what the driver is when you feed it sq wave... Has no chance to cool moving from +peak to -peak through the region where current flow is decreasing to zero and then reversing... It can start cooling right off of peak as current drops.... Square wave positive peak does not drop. It BECOMES negative peak. Transition is almost perfectly vertical...no time duration between alternation, no cooling time....
What all gets smoked is determined by who didn't follow worst case scenario design step in component ratings...


Mondays were sometimes like reruns... and they wouldn't usually 'volunteer' they blew shit up either... If a 300lb anvil was a speaker, some of the boss's regular equipment renters could tear the damn thing up in ten millisecs.... with a used toothpick.... just trying to turn the damn thing on....

I just did what I was told....and replaced drivers... and worked on occasional amps... I let him deal with the Bufords on replacement charges....
 

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There's another Pulsonic cone G12H 55Hz greenback I have that's entirely seized up. The coil reads fine and the speaker passes a signal and sounds pretty normal at very low volumes (I didn't dare crank it). The cone won't budge even a little, though. It's as if there's some glue or gummed up something in the gap. It's a very clean speaker, physically, though. I've never made a decision about what to do for it, so its just sat on my shelf of old injured soldiers, waiting for me to learn surgery so I can fix them up. I'm collecting a small army of old guitar speakers, so I had better learn!
 

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There's another Pulsonic cone G12H 55Hz greenback I have that's entirely seized up. The coil reads fine and the speaker passes a signal and sounds pretty normal at very low volumes (I didn't dare crank it). The cone won't budge even a little, though. It's as if there's some glue or gummed up something in the gap. It's a very clean speaker, physically, though. I've never made a decision about what to do for it, so its just sat on my shelf of old injured soldiers, waiting for me to learn surgery so I can fix them up. I'm collecting a small army of old guitar speakers, so I had better learn!

I make no attempt to fix speakers. I just send them off and let the pros do it.
 

cooljuk

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I make no attempt to fix speakers. I just send them off and let the pros do it.
That's what I've always done in the past, too. Weber has generally sent me back reconed speakers that sound better than the others from the same cab that were original and in fine shape. It's those old Celestions, though. The Pulsonic, RIC and maybe even later Kurt Mueller cones. That's where all the monetary value is. I definitely hear it, too, at least with the Pulsonics, so I'll put some real world useful tool value on the Pulsonic cones, too. Without the original cone, they just sound like modern reissues and loose their voice. I think my goal now is to learn surgery on the RIC cones, then to a great job on the Pulsonic cones.

I have a bunch of old wire in various sizes and insulations that might work for repairing the coils, too. I do have at least one with an open coil. Repairing a voice coil is the one part of the job I'm very confident in being able to complete well.
 
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Soul Tramp

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That's what I've always done in the past, too. Weber has generally sent me back reconed speakers that sound better than the others from the same cab that were original and in fine shape. It's those old Celestions, though. The Pulsonic RIC and maybe even later Kurt Mueller cones. That's where all the monetary value is. I definitely hear it, too, at least with the Pulsonics, so I'll put some real world useful tool value on the Pulsonic cones, too. Without the original cone, they just sound like modern reissues and loose their voice. I think my goal now is to lear on the RIC cones, then to a great job on the Pulsonic cones.

I have a bunch of old wire in various sizes and insulations that might work for repairing the coils, too. I do have at least one with an open coil. Repairing a voice coil is the one part of the job I'm very confident in being able to complete well.

You know, there probably is therapy for this compulsion/obsession! :rofl: :rofl:
 

cooljuk

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Them damn duty cycles'll get ya every time....

Saw a cone in a floor catch fire once.... Waaaay too much wattage.....no crowbar.....


Decades back, worked at a musico and boss loved renting out small PA stuff on weekends.... I usually spent time first of week replacing drivers.... Kept a pile of motorola cheap ass tweeters and the little horns in the shop...
DJ mixer into a PA mixer channel into a power amp into drivers.... Rented by folks that think when they see blinking leds, everything is cool....especially them red ones... What can happen? :laugh2:

Like a damn game of which stage goes sq wave first... Don't much make a damn what the driver is when you feed it sq wave... Has no chance to cool moving from +peak to -peak through the region where current flow is decreasing to zero and then reversing... It can start cooling right off of peak as current drops.... Square wave positive peak does not drop. It BECOMES negative peak. Transition is almost perfectly vertical...no time duration between alternation, no cooling time....
What all gets smoked is determined by who didn't follow worst case scenario design step in component ratings...


Mondays were sometimes like reruns... and they wouldn't usually 'volunteer' they blew shit up either... If a 300lb anvil was a speaker, some of the boss's regular equipment renters could tear the damn thing up in ten millisecs.... with a used toothpick.... just trying to turn the damn thing on....

I just did what I was told....and replaced drivers... and worked on occasional amps... I let him deal with the Bufords on replacement charges....

I maintained some pretty big club PAs in my day. For some reason, DJs are the worst with redlining their mixers. For most of them, there's hardly any musicianship involved and all they have to worry about is the sound, but for some reason they all want to start at unity gain and work their way up well beyond that, over the course of an hour or two set. Of course, no club owners want to pay to over-spec the PA so headroom is never a solution. Usually, it involves the son or nephew of a club owner sitting on a stool and occasionally reaching over the DJ to turn a gain knob down. There can be quite a bit of ego for even nephews with the longest arms to reach over. Not a job I'd want.

In a rental situation, there's no nephew or son. I know the pain of those rented systems. One of my first professional gigs repairing music gear was an authorization for Panasonic, so I could maintain all the Technics SL-1200s that got regularly trashed in Baltimore. Though they are tanks, as far as turntables go, turntables probably see about as much abuse in a club or a mobil rig as a gigging pedalboard.
 
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