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Vibration damage

rdmjazz

rdmjazz

Aug 29, 2000
474
26
Tampa Bay, Florida
#1
Just curious, does anyone use any type of padding between your head and cabinets?

I just had an amp repaired that had a couple of capacitors break loose. The repair tech said they broke probably from vibration.

I never really thought much about it, but man the low end does really shake the crap out of my rack.:eek:
 
#3
rdmjazz said:
Just curious, does anyone use any type of padding between your head and cabinets?

I just had an amp repaired that had a couple of capacitors break loose. The repair tech said they broke probably from vibration.

I never really thought much about it, but man the low end does really shake the crap out of my rack.:eek:
Click to expand...

I've been doing that for years for exactly that reason. When using a separate head, I bring along a piece of dense foam, 2" thick, cut to the size of the bottom of the head. I don't know if it does anything but I've never had an amp fail from vibration. When I had a large amp head in an SKB rack, I had one extra rack space above the head and I used to slide the foam inside there to carry it around.
 
#4
Except where a desperate lack of space forces us to do so, there's no sensible reason to mount our amps on top of / in physical contact with our cabs at all. We still do it, though.

Well.... Looks good, dunnit. :D
 
#7
I use a 2" thick foam pad inbetween my rack and my 2x15 cab, mainly because of the rattling noises I could hear from the rack case vibrating, and the spring loaded handles on the cab. Works great.
 
#9
Your head would suffer far more vibration damage in a single load-in/load out cycle than from sitting on top of the cab during the interim. If the cab is vibrating enough to damage the amp it's also vibrating enough to seriously impact performance. You can put a drink atop a well made cab at the beginning of your set and it will still be there at the end. If that's not the case with your cab it's in need of bracing. But beyond that, if cabinet vibration was innately a source of amp damage, what about combos?
 
#10
billfitzmaurice said:
Your head would suffer far more vibration damage in a single load-in/load out cycle than from sitting on top of the cab during the interim. If the cab is vibrating enough to damage the amp it's also vibrating enough to seriously impact performance. You can put a drink atop a well made cab at the beginning of your set and it will still be there at the end. If that's not the case with your cab it's in need of bracing. But beyond that, if cabinet vibration was innately a source of amp damage, what about combos?
Click to expand...

I don't think the drink on top point is valid at the volumes I'm playing at. I'm having to cover rooms without PA help or playing outdoors in concert settings. At higher volumes the sub frequencies are gonna rumble no matter how your cabinet is built.

I have a friend with a repair shop who says he has been getting many powered subs in with damage due to vibration. I would think the manufacturers would take that into consideration when designing the amps.

Anyway, I found a nice perfect sized black vinyl cushion that my rack sits on now, better safe than sorry I suppose since I can't afford repair shop rates!:rolleyes:
 
#11
rdmjazz said:
I don't think the drink on top point is valid at the volumes I'm playing at. I'm having to cover rooms without PA help or playing outdoors in concert settings. At higher volumes the sub frequencies are gonna rumble no matter how your cabinet is built.
Click to expand...

Good point!

Also: even if the cabinet itself doesn't rumble, the stage underneath it might.
 
#12
rdmjazz said:
At higher volumes the sub frequencies are gonna rumble no matter how your cabinet is built.
Click to expand...
Mine don't. When I test my subwoofer prototypes I feed them 30 Hz sine waves at full power to be sure that there's no vibration. If they vibrate they get more bracing. It's more than a matter of being able to use your cab to hold drinks. Energy that's expended vibrating the cabinet walls is energy not radiated as sound. An efficient cabinet is an inert one.
 
#16
If you DO need some isolation you don't need 2" open cell foam - just grab a cheap closed-cell backpacking sleeping mat from Wallyworld or wherever that's maybe 1/4 the thickness and cut it up for this and whatever else you need.

I actually use my 4 space rack for only a one-space Peavey DPC-1400X power amp, so there are three spaces open. But when I'm about the schlep gear I put the foam "isolator" in between the amp and my V-Bass unit and various cables and a fold out bass stand I made, to keep stuff from getting scratched or bashed.
 
#18
billfitzmaurice said:
My point is you should never have a drink further away from you than your amp. :D
Click to expand...

And then the drummer next to you looses a stick as he goes to crash a cymbal,the stick hits the half empty beer bottle on your amp, knocking it over, pouring beer all down the front. True story!
 
#20
billfitzmaurice said:
Your head would suffer far more vibration damage in a single load-in/load out cycle than from sitting on top of the cab during the interim...
Click to expand...

There is an element of truth to this. The shock levels caussed by knocking the head around during loading and unloading are probably more than ten times the level of the vibration from sitting on the cab. But the vibration from the cab is sustained over a much longer period of time and that can cause fatigue damage in a poorly designed or a poorly built amplifier.

Large power supply capacitors are especially vulnerable to fatigue damage. If they are left supported only by their leads then they will resonate to low frequency vibration. Eventually the leads fatigue at the solder joints and break off. This could happen even if the cab is well designed and does not resonate itself.

Padding definitly improves the situation but epoxying the power supply caps to the board is an even better solution.
 

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