What now? (cabinet troubleshooting)

[Noose]

GK 410 SBX +
Speakers were working fine until about an hour into band rehearsal, i start noticing a buzzing speaker

I checked all the screws and everything is tight. Looked over the cones of all the speakers from the outside and found no visible damage except for a small hole in the dustcap of one of the speakers. It looks like a small screwdriver had punctured the dust cap and the previous owner had patched it with some type of rubbery black sealant. (possibly liquid elctric tape) Just to be sure, I put a small patch over the are using a peice of coffee filter and some Krazy glue. This didnt change anything in regards to the buzz.

So i took the speakers out of the cabinet. Pushing in on the cones produces no scratchiness. Did the battery test, but Im not exactly sure what I am looking for using this method. The cones of all the speakers push out when I put the battery to the terminals. No strange sounds, no scrathiness from the voice coils. I assume this means the voice coil isnt burnt. Not all of the speakers are buzzing, but all of the speakers behave the exact same way when pushing in on the cone or using a battery. I cant find any places where the glue has failed, no loose wires, nothing at all.

What next? Is there something else I should be looking for that is common? Should my next step be to take it to a repair shop?

[craig.p]

Just a guess here, but it's possible the drivers were abused just enough to have caused the coil forms to go and remain out of round just enough so that now, when they heat up, they go just further enough out of round to scrape. By the time you shut down and begin to investigate, things have cooled down and have returned to approximately cylindrical. Not perfectly cylindrical, but cylindrical enough so that the scraping no longer occurs. We're talking tiny fractions of an inch here.

Again, just a SWAG on my part.

You said not all the speakers are buzzing, so I assume that means you've narrowed it down to one or two.

The other thing to check is that the drivers are snugged down in the correct sequence, i.e. star pattern rather than circular pattern, so you don't warp the frames. A warped frame can cause the same symptoms you describe. And remember, don't sock those screws down, just snug 'em up.

[Noose]

Originally Posted by craig.p

Just a guess here, but it's possible the drivers were abused just enough to have caused the coil forms to go and remain out of round just enough so that now, when they heat up, they go just further enough out of round to scrape. By the time you shut down and begin to investigate, things have cooled down and have returned to approximately cylindrical. Not perfectly cylindrical, but cylindrical enough so that the scraping no longer occurs. We're talking tiny fractions of an inch here.

Again, just a SWAG on my part.

You said not all the speakers are buzzing, so I assume that means you've narrowed it down to one or two.

The other thing to check is that the drivers are snugged down in the correct sequence, i.e. star pattern rather than circular pattern, so you don't warp the frames. A warped frame can cause the same symptoms you describe. And remember, don't sock those screws down, just snug 'em up.

Man I hope you are wrong but I'm beginning to worry that you might be right.

[Electricblue]

Check that no wires are resting against the back of the cone, give the terminals a wiggle when the speaker is making sound, give everything a firm knock and see if it stops.

Try running the speaker not mounted in the cab if possible.

Write down all the stuff you have checked and eliminated.

[Electricblue]

Sorry for the double post, you said it had a hole in the dustcap? make sure nothing is in there, it may have been shot with a bb gun or something like that.......

[craig.p]

> Try running the speaker not mounted in the cab if possible.

Don't do that.

[Electricblue]

Originally Posted by craig.p

> Try running the speaker not mounted in the cab if possible.

Don't do that.

Obviously not at full beans, just to check that the rattle is not cab-related.

[Noose]

Originally Posted by Electricblue

Sorry for the double post, you said it had a hole in the dustcap? make sure nothing is in there, it may have been shot with a bb gun or something like that.......

Can that be done without removing the dustcap?

[Electricblue]

Originally Posted by Noose

Can that be done without removing the dustcap?

Shake it vigarously, give it a whack from behind to dis-lodge anything that might be in there.

[christw]

Originally Posted by Electricblue

Obviously not at full beans, just to check that the rattle is not cab-related.

+1

It's an easy way to do the "push test" and listen for any speaker related rattles.

[mikeddd]

I just returned an Eminence Basslite 2010 for this same problem. But mine was new in the box. Sorry...no contribution to this thread...just sayin.' Carry on.

[Noose]

Oh I left out what may be important info to mention.

The buzz isnt noticable unless I am playing low notes. Can't hear it when I'm playing in the upper part of the neck or if I'm playing fairly quietly.

Not sure if that changes anything.

When people refer to wires rattling against the cone, are they referring to the two small wires that are attached to the cone? If so, is there a way to keep them from doing that?

Also, I was considering applying a bead of silicone or caulk to act as a gasket where the speakers mount to the cab. Is this a bad idea?

[Electricblue]

Originally Posted by Noose

Oh I left out what may be important info to mention.

The buzz isnt noticable unless I am playing low notes. Can't hear it when I'm playing in the upper part of the neck or if I'm playing fairly quietly.

Not sure if that changes anything.

When people refer to wires rattling against the cone, are they referring to the two small wires that are attached to the cone? If so, is there a way to keep them from doing that?

Also, I was considering applying a bead of silicone or caulk to act as a gasket where the speakers mount to the cab. Is this a bad idea?

Are you pushing the speakers too hard?
Is it your bass thats rattling?
Are the wires rattling?

[craig.p]

> Also, I was considering applying a bead of silicone or caulk to act as
> a gasket where the speakers mount to the cab. Is this a bad idea?

Speaker gasketing is available. I think Parts Express has it, and probably others, too.

What do the current gaskets look like?

[billfitzmaurice]

The only way to isolate the source of buzzing is with a sine wave generator, so you can sweep the frequency and listen closely without an instrument in your hand. Google tone generator to download one to your laptop, you'll need a 1/8 to 1/4 cord to send the signal from the laptop to your amp.

[craig.p]

Lower notes and/or higher volume = more cone movement. Lines up with that you've already told us.

Yes to your question about the two small wires. You can either tie-wrap them down somewhere (wrap them in electrical tape first so you don't pierce the insulation, and go easy on the tie-wrap tension), OR you can rotate the speaker so the wires hang away from the cone. I usually do it the second way, FWIW.

[Noose]

Originally Posted by craig.p

> Also, I was considering applying a bead of silicone or caulk to act as
> a gasket where the speakers mount to the cab. Is this a bad idea?

Speaker gasketing is available. I think Parts Express has it, and probably others, too.

What do the current gaskets look like?

Non existent. The cab is covered with that rat fur stuff and it extends all the way to the cut out that the speakers sit in. I'm guessing this was done on purpose for it to act as a gasket.

E

[Noose]

Originally Posted by craig.p

Lower notes and/or higher volume = more cone movement. Lines up with that you've already told us.

Yes to your question about the two small wires. You can either tie-wrap them down somewhere (wrap them in electrical tape first so you don't pierce the insulation, and go easy on the tie-wrap tension), OR you can rotate the speaker so the wires hang away from the cone. I usually do it the second way, FWIW.

Didn't think to try that. Sounds like a good tip.

[delta7fred]

Originally Posted by craig.p

Yes to your question about the two small wires. You can either tie-wrap them down somewhere (wrap them in electrical tape first so you don't pierce the insulation, and go easy on the tie-wrap tension), OR you can rotate the speaker so the wires hang away from the cone. I usually do it the second way, FWIW.

I think Noose is referring to the flexible wires that connect the terminals to the cone, not the wiring in the cab. Don't tie-wrap the former to anything.

[mikeddd]

Tone generator. http://www.burninwave.com/generator_dl.htm