Speaker Problem

[GregS]

A while back at a gig there appeared to be a problem with a speaker cabinet which I had built. It was making a crackling noise (best word I can find to describe the symptom) when the guitar was played through. We tried another amplifier head and the crackling was still there so it was not the amplifier. We took the pedal board out and went straight into the amp so that wasn't the problem either. We didn't try another guitar. However I don't think that would be likely as if there were a bad connection in the guitar wiring I would expect to hear the problem all the time - playing or not. Also, it seemed to me that the crackling was coming from one of the two 12" speakers which would isolate the problem to the speaker.

The speakers are Celestion G12H Anniversary Edition and are only 2 years old. The cabinet has not seen too much use and the speakers have never been pushed anywhere near the limits.

Afterwards, I checked that the solder joints and wiring were all good in the cabinet - both with close visual inspection plus I hooked up my Ohmmeter to it and pulled and wiggled all the wires and joints. The meter was steady as a rock at around 3.8 Ohms the entire time which rules out an intermittent connection. I played the cabinet for about 20 -30 minutes at all volume levels and could not recreate the problem.

The gig we played was outside on a very hot day with intense sun right on the speakers. I used a screen door mesh for the grill cloth which does little to block the speakers from the light. I'm wondering if the speaker heated up abnormally causing parts to expand and possibly the voice coil was contacting something in the gap it moves in? - and now that it has cooled and everything shrunk back to it's normal size it's moving freely again? Or maybe some piece of junk got into the gap and has now found its way out?

Any input on why this happened and why it's not happening now would be greatly appreciated. I'd hate to assume all is ok and have the problem re-appear at another gig.

Thanks,
Greg

[Jazz P Bass]

If you did indeed narrow the issue down to the one speaker, then that is the one to keep an eye (ear?) on.
The sunlight very well may have been the problem.
The "gap" in the voice coil ideally should be perfectly centered.
Sometimes this is not always the case & weird stuff happens.
If you have to play the cabinet "in the sun" maybe you should use a real grill cloth.

[guitician]

How did you space the grill cloth/screen from the baffle? I had a problem where the cloth was slapping up against the baffle causing noises. The vibration of the cabinet can transfer into the screen causing it to rattle against the baffle. Those speakers are made with some pretty good adhesives that can take a lot more heat than the sun shine would bring.

[g1]

Loose bracing or a crack in the cab could also cause this. You need to isolate whether it is indeed one particular speaker or the actual cabinet.

[GregS]

Thanks for the replies.

How did you space the grill cloth/screen from the baffle? I had a problem where the cloth was slapping up against the baffle causing noises. The vibration of the cabinet can transfer into the screen causing it to rattle against the baffle. Those speakers are made with some pretty good adhesives that can take a lot more heat than the sun shine would bring.

This problem only occurred on one occasion so I don't think this likely. It has been used for a number of hours without problem. Also the sound was too loud and didn't seem like the kind of sound that that would make.

I was thinking more about parts expanding as a result of becoming extremely warm such that the voice coil was no longer moving freely in the gap. The heat on the equipment was serious - probably almost enough to melt plastic. We had to cover as much of the equipment as we could with blankets we had.

[GregS]

Loose bracing or a crack in the cab could also cause this. You need to isolate whether it is indeed one particular speaker or the actual cabinet.

There is nothing loose or cracked in the cabinet. It's made from very substantial 3/4" plywood and is very solid. I'm not able to zero in on whether it was one speaker or what it was at this point as it's working fine now. I can't recreate the problem. My concern is that it will resurface at an inconvenient time - like at a gig again. Anyway unless it re-appears I think it will be forever inconclusive as to what caused it. The only thing I can do now is use it regularly and get some confidence level that all is ok before taking it to another gig.

If you have to play the cabinet "in the sun" maybe you should use a real grill cloth.

I am going to change it to real grill cloth. I have been using proper grill cloth on cabinets I have built since and it looks a lot better as well as protects better. I had another one of my cabinets at the same gig with real grill cloth and it did just fine.

Greg

[gbono]

Look at the tinsel leads that go from the VC to the terminal block on the speaker - are they rubbing on the diaphragm (cone)?