Reducing vibrations & rattles - seeking ideas on cab design

[tubeswell]

Okay I want to eliminate as many vibrations as I can. The amp chassis is mostly quiet on a lot of notes but F# and G on the low strings seem to make the chassis vibrate hell for leather when its cranked. I pulled out all the unconnected/loose socket pins and tightened all the screws and nuts I can find, and have tapped endlessly all over the chassis trying to find the source of any noises. I also put door seal strips between all metal and wood surfaces.

So I am thinking it must be some kind of resonant frequency thing going on, that could possibly be amelioraed with improved cabinet design. I have the baffle mounted on two side battens from the rear, with 4 PK screws in each batten. (see pics - please ignore the crappy speaker).

Is there a better way of mounting the baffle to reduce the amount of vibration gettig through to the chassis? (Should I remove the number of contact points between the baffle and the battens - possibly by taking out some of the length of battens?, or should I add more battens to top and bottom?)

[Sir Cuitous]

One of my co-workers had a resonant frequency on an immaculate '66 Fender Pro that he had just bought (uh-oh). The only way we could diagnose was for me to "crank" the notes and for him to carefully check the cab/chassis by hand pressure. It was the electrolytic, filter caps which are on their own little board and covered with a metal cover on the bottom of the main chassis. Fender must have known that the small board with the caps would vibrate so they put a strip of padding between the caps and the metal cover. Over time the padding had dried up and allowed the small board and cap assembly to vibrate. We literally shimmed the padding on the inside of the cover back up to hold the caps in place and the resonant frequency was gone. Can you get someone to play those F#s and Gs while you check?

[tubeswell]

Yeah it could be something like that - its hard to detect when I am trying to play the notes and dampen various bits of outside of the chassis with my hand. It doesn't appear to happen on all frequencies, only the ones around F# and G. Is there some scientific (or pseudo-scientific) way to 'tune' a cab's resonant frequency to get it below bottom E - or bottom D if dropped tuning ;-)?

Would adding battens to the inside top and bottom of the baffle reduce boominess?

[cminor9]

Pseudo-scientific? Wave a dead chicken over it. Sheeps' bladders have been known to stop vibrations, as well. Finally, if all else fails, drink a concoction consisting of...

Or not. Do you know where it's coming from? As in the chassis or the cabinet? How did you do your cabinet joints? Did you adequately glue all your finger joints if that's what you used? Maybe try sitting on your cab to see if that dampens the rattle? That would probably tell you that you have a loose joint somewhere.

Also, the strips around the perimeter of the baffle like to vibrate if you don't glue them down well enough. Mine sure did. Maybe try pressing against them at various points to see if that stops it?

When I built my cabs, they didn't rattle (finger joints) but after a few weeks the perimeter around the baffles did. A few screws fixed the problem for me. Guess I didn't glue them well enough and they vibrated loose.

[tubeswell]

Hmmm... dead chicken aye? Maybe I could sacrifice my neighbour's cats, who indiscriminately poop all over my back lawn ;-) Caused me no end of grief yesterday morning when I accidentally trod through the house with remnants of it still attached to my boots'n'all (which coincidentally was Friday 13th).

Anyhow I'm sure it's in the chassis, because I can dampen the vib by touching the chassis top. I guess I'll just go on plodding along.

But I was wondering whether it is possible to reduce cabinet boominess by various means, but whether it involves tightening the cab by putting in more internal battens, or loosening it by removing some, or adding ports to teh baffle or filling the box with accoustic padding - I guess I need to do some more experimenting to find out. The cab is quite big, so maybe it needs some rethinking

The idea of a floating baffle - is that to 'deaden' the cab resonance a bit?

[cminor9]

From what I have read, and I am certainly not an expert, the floating baffle is designed to enhance the cab's vibration. A floating baffle is usually made of thinner wood (< 1/2"). Using thicker wood, or a baffle that is *part* of the cab or surrounded completely by battens would reduce baffle vibration. Many opine that would be bad and would result in a "dead" cabinet. You asked about more battens to the top and bottom. That was the first thing I thought when I actually took a good look at the pics. But you think it sounds like it's the chassis, so maybe you don't need them. I'd try to let it float as much as possible. Like I said, I am not an expert but I have done a lot of reading and it just makes sense that a floating baffle would be more resonant in a good way.

Since you can isolate it to the chassis, I would try first making sure that the chassis itself (or something attached to it?) isn't rattling against the cab. Hope it's not some internal part, that would be a pain to troubleshoot.

Are your filter caps vibrating against the board? I used silicone caulk to attach mine to the board. I saw someone else suggested damping the "doghouse" over your filter caps. Looking at your pic, the transformers look very close to the baffle. Might that be vibrating against the baffle and then transmitting the rattle through the chassis? Sorry if that sounds crazy, just trying to brainstorm.

[tubeswell]

follow-up

Well yesterday I went over the whole cab and chassis and put rubber door seal strips between all the contactable surfaces and spacers between the terminal tag strips and the chassis in the doghouse. I tried it out tonight at band practice and the rattles seem to have gone. Here's hoping they don't come back anytime soon ;-)

So thanks for that suggestion Cminor9. (BTW Hope you can make up your mind easily about your next build. I get tied up in knots about the choice. I am thinking about a 5E3 next (or maybe a 5E5a? )