Cab / Head vibration issue...

[Ant1977]

A few examples for you to ponder over

Why is it...

When I use my Marshall 4x12" Cab (which is on casters)
On my carpeted basement floor, my head begins to vibrate off...

Have not noticed the same on bare concrete floor.

Also,

When I am at rehearsal, using my GenzBenz 2x12" (not on casters
but on my guitarist's Workout Mats, like these) -
http://www.sportsauthority.com/produ...entPage=family
My head begins to vibrate off...

Again, have not noticed the same on bare concrete floor.

And this is no light head... It's my Mesa 400+... In a rack... with a Monster Rack power supply... The whole thing is heavy as hell.

Because I do not know what the floor conditions will be from gig to gig, what can I do to prevent my rack from ever vibrating off the cab?

*And please don't say put the rack on the floor as that is almost never an option.

Thanks for the help.

[smogg]

Just put a piece of soft foam or whatever between cab and head/rack.

[Ant1977]

Originally Posted by smogg

Just put a piece of soft foam or whatever between cab and head/rack.

Ok, I just checked it.
The whole rack comes to almost 55lbs
The rack has rubber feet on the bottom which make full contact with the cab.
I would think a piece of foam would make it slide even easier, no?

[Ant1977]

Pics...

[fingertap]

I have the same problem, head vibrating off cab.

The initially soft rubber feet on the head have turned rather hard and shiny-glazed over the years.

I purchased some "Grip Liner" at a hardware store.
Con-Tact brand from Kittrich Corporation.
Cost about US$ 4.00 for a roll 20 inches by 5 feet.

Haven't tried it yet but I suspect that it will work.
The stuff keeps dishes from vibrating off shelves during earthquakes.


~

[smogg]

Originally Posted by Ant1977

Ok, I just checked it.
The whole rack comes to almost 55lbs
The rack has rubber feet on the bottom which make full contact with the cab.
I would think a piece of foam would make it slide even easier, no?

The feet are probably no where near soft enough, especially on a vinyl covered cab. 1/4" or 1/2" thick soft foam will help absorb the vibrations and limit sliding.

[billfitzmaurice]

The cause of the head dancing is insufficient (if not non-existent) internal bracing of the cab. The resulting vibration of the cab walls causes the amp to move, and also costs you output, as the energy that vibrates the cab is wasted power. The best cure is internal cross bracing. Even a single 1 inch dowel connecting the middle of two opposite panels will reduce vibration as much as doubling the panel thickness.
A piece of 1/2" thick high density foam between the head and cab will stop the head dance; you can get it at any Walmart in the sporting goods section, where it's sold as a camping mattress pad.
But foam only addresses the symptoms, rather than fixing the root cause. If you do open the cab to add bracing while you're in there make sure it's fully lined with foam, fiberglass or polyester damping. Damping, like proper bracing, is often under utilized, if not completely omitted, because you can't see it.

[fingertap]

Every time I have experienced this 'head dancing'
it has been on uneven ground, dirt, grass, or tilted (5degrees+), elevated stages at loud volume.

I know this cab needs some additional internal bracing, and thanks for pointing this out.

Maybe it was a crime for me to fail to indicate to the OP that the measure I undertook was palliative.

The feet under the head have become 'glossy' and much harder
and more slick than they were forty years ago,
when, as I remember, they were much softer
and the cab's exterior (tolex) has been treated with a product (armor-all? or simply age itself)
which has made it more like a 'non-stick' frying-pan coating.

That is my case, the OP's case may be different
and I failed to discriminate.

Busted.