Celestion G12T-75 Speaker Rattle problem

[zw44]

Hi,
There is a distinct rattle from one of the Celetion G12T-75 speakers in my jcm900 2x12 combo. I have taken the speakers out of the enclosure to ensure it wasnt something in the cabinet rattling. I am certain the rattle is coming from just one of the speakers. It only occurs at certain frequencies. I have measured its DC resistance and it seems normal for a 16 ohm speaker. I can't see any cuts or holes in the speaker cone. It sounds very much like a rattlesnake!

What the hell could the problem be? It seems more pronounced when playing clean, but I assume that is because it doesnt blend in with any distortion.

Any help is greatly appreciated!

[52 Bill]

What the hell could the problem be? It seems more pronounced when playing clean, but I assume that is because it doesnt blend in with any distortion.

There are any number of things that can rattle or buzz. Check anywhere there is a glued contact, like where the cone meets the frame, or where the spider meets the coil former or the frame, etc. The dust cap is another common item that will cause that kind of buzz.

I like to send a signal through the amp that will cause the buzz and then I'll lightly touch the different parts of the speaker, to see if I can cause the buzz to stop or change tone, which will usually lead me to find the loose component.

[leprof31]

I do have the same problem with my G12T after I pushed my Combo Marshall JMP very hard on overdrive(Hendrix way). The rattle is audible when I play clean, without distortion. I think these speakers are just gone... like if the center have shift a bit. Very sad, they was old 70' speakers.

[gbono]

maybe check the tinsel leads from the voice coil to the tag panel. If the leads touch the cone during excursion you will get all sorts of noise (usually at low frequencies).

The cone and VC may be off center as well. You need a signal generator to really get a good diagnosis - maybe find a "software" based signal generator (does anyone have a favorite = cheap/free??).

If you are really nurdy you can find a way to measure the impedance plot for the driver and the drivee in its enclosure- again you might find a cheap software solution for this as well - MLSSA and Liberty Audio (PRAXIS) are very good tools but $$ and the learning curve is steep.

[tubeswell]

Does the same rattle happen without that speaker in the cab? (Could be in the cab??)

[zw44]

I do have the same problem with my G12T after I pushed my Combo Marshall JMP very hard on overdrive(Hendrix way). The rattle is audible when I play clean, without distortion. I think these speakers are just gone... like if the center have shift a bit. Very sad, they was old 70' speakers.

Yea I ended up giving in and replacing the speaker. To make it all worthwhile I tore the old one apart to check out the internals.... there isnt much to see!