Anti-shock feet for amp?

**Matthew_84** · #1 10-26-2011, 07:05 PM

Hello TBers,

So in another thread today it came to my attention that I need some feet on the bottom of my power amp to prevent the vibrations coming from the cab that the amp is sitting on.

There is one condition though, my cab has a single handle on the top of it, so I need the feet to be at least 3/8" thick to clear the handle.

Right now I have 4 pairs of round felt pads that are stacked on top of each other, but I'm not certain if the felt pad feet are really doing much to absorb the vibrations, and not transfer them to the body of the amp.

Any suggestions or opinions are welcome and very much appreciated. Thanks,

Matt

will33 · #2 10-26-2011, 07:26 PM

The felt is probably doing the job. I don't know of any actual shockmount feet but softer rubber tends to soak up vibrations more than the harder rubber or plastic.

**Matthew_84** · #3 10-26-2011, 07:39 PM

Hmmmm... Yeah, I'd like to try out some kind of rubber feet, but the felt pads are somewhat soft.

I still plan to move the rig outside to isolate the rattle sounds, but I do know that the top of the amp housing rattles...

I'm going to place the amp on another surface to see if still rattles, which will tell me if it's a vibration by location issue, or if it's related to certain frequencies.

waleross · #4 10-26-2011, 07:57 PM

In my studio, I use Auralex acoustic Gramma Panels(large ones) . They are foam bottom boards that stabalize my bass heads on top of the cabs. These are used to place underneath cabs but I tried it this way and it works. They are expensive ($85) but being versatile I get use out of them . This is just a suggestion...........................

will33 · #5 10-26-2011, 08:01 PM

The gk mb cabs don't have any bacing inside and can vibrate at louder volumes. That may be part of it. Wood floors, other stuff in a house (like china

) can vibrate sympathetically with frequencies and thus vibrate the rig that's sitting on the floor. Smart move to separate all the components to isolate the problems. There's a fairly long thread in here somewhere about bracing and lining the mb cabs so they're more solid, improved performance, etc.

johnk_10 · #6 10-26-2011, 08:10 PM

i make my own out of sorbothane. IMO, nothing provides better shock isolation than that stuff.

hrgiger · #7 10-26-2011, 08:30 PM

I was thinking, my HK turntable has some really nice large 'floating' anti-shock feet on it, you may be able to get some sort of DJ turntable feet. it really depends on the weight of your amp, it would require more feet then I suppose it would work well.

ebay has an assortment maybe a good starting point for your search to at least see what I'm talking about.

I believe turntable feet are more to isolate 'impulse' type shocks not sure they would isolate consistent vibrations from a cab.

**Matthew_84** · #8 10-26-2011, 08:40 PM

Well, I seperated the two and the rattling went away. Ran into something funny though: the amp's housing only vibrates when it is on top of the cabinet AND when I play an E, but not any E, only the open string E, the 12th fret on the E string, and the 7th fret on the A string. It does not rattle on the 2nd fret of the D string or any other E note on the D or G strings for that matter, and it also doesn't rattle on the 19th fret of the A string. But, the rattling is the strongest on the 12th fret of the E string, or the 7th of the A, it is actually a bit tamer on the open E string and again comepletely non existant on the 2nd fret of the D string.

Quote:

Originally Posted by waleross

In my studio, I use Auralex acoustic Gramma Panels(large ones) . They are foam bottom boards that stabalize my bass heads on top of the cabs. These are used to place underneath cabs but I tried it this way and it works. They are expensive ($85) but being versatile I get use out of them . This is just a suggestion...........................

Good idea, I actually built my own gramma pad, custom fitted for this cab and it works great and only cost me about $50 to make. The ground doesn't rumble at all, very impressed. I basically looked at various photos and made my own out of a plywood board with a couple thin sweaters stapled down onto it and wrapped a black leather sheet around it and stapled on the underside. I used pink styrofoam insulation, glued three 1" sheets together and used those at the feet, and wrapped them in black tape to not show the pink, and I put some egg-carton foam on the underside.

Maybe recreating a smaller version isn't such a bad idea.

Quote:

Originally Posted by will33

The gk mb cabs don't have any bacing inside and can vibrate at louder volumes. That may be part of it. Wood floors, other stuff in a house (like china

) can vibrate sympathetically with frequencies and thus vibrate the rig that's sitting on the floor. Smart move to separate all the components to isolate the problems. There's a fairly long thread in here somewhere about bracing and lining the mb cabs so they're more solid, improved performance, etc.

Will, if you're talking about this thread, GK 410MBE Mods then I am already on it. I am planning on putting a pillow worth of stuffing in there in the next day or so... just so busy fiddling round with other things.. LOL, but that's a good point to bring up and I'm glad you did, maybe the two issues are related. If the link I posted is not the link you're referring to, can you please let me know? You don't have to find the link, I can do that myself. And thanks again for your help Will.

Quote:

Originally Posted by johnk_10

i make my own out of sorbothane. IMO, nothing provides better shock isolation than that stuff.

that stuff looks pretty pricey, but it's making me think again about a revised amp gramma pad.

But maybe the gramma pad I made isn't working as well as I thought, or else a bunch of stuff in the room wouldn't be rattling as well? Well I guess it could be with the airborne frequencies no? As mentioned in another thread, a lof of the stuff that's rattling is china, and different things rumble on different notes. I haven't found one thing rattle on two seperate notes, even chromatic ones.

**Matthew_84** · #9 10-26-2011, 08:41 PM

Quote:

Originally Posted by hrgiger

I was thinking, my HK turntable has some really nice large 'floating' anti-shock feet on it, you may be able to get some sort of DJ turntable feet. it really depends on the weight of your amp, it would require more feet then I suppose it would work well.

ebay has an assortment maybe a good starting point for your search to at least see what I'm talking about.

I believe turntable feet are more to isolate 'impulse' type shocks not sure they would isolate consistent vibrations from a cab.

Thanks, I will check those out as well, would likely be cheaper than my endeavour, since I threw most of the materials out.

will33 · #10 10-26-2011, 09:47 PM

I was thinking of this one. Just opened up my 210MBE.... but I think we're talking about different cabs here. The sealed 410 appears to have some degree of bracing but I've never seen the whole inside of one. Yours should be lined at the least. Perhaps more or less stuffing to taste. Would just have to listen to it.

That thread is pretty long but there are some pics in there somewhere from folks who did the mods. If yours doesn't vibrate when you play it outside on the ground it's fine. Your vibrations would then be soundwaves vibrating the floor in the house and in turn, vibrating the cab that's sitting on the floor....like a loose wooden stage.

seamonkey · #11 10-26-2011, 09:49 PM

You can keep them separated with a stand for the head
This one is actually very sturdy and fully adjustable.
QLY-02 Keyboard Stand from audioMIDI.com

**Matthew_84** · #12 10-26-2011, 11:36 PM

Thanks for posting that link Will. I had actually ran across that thread a couple of times but completely forgot about it.

Well, it really seems like I have to line this cab. I do find it to be on the boomy side tonewise, and I'm pretty sure that reducing this boom will also cure some of the vibrations I'm dealing with.

I'm actually kind of annoyed with GK over this and other things I've mentioned in other threads today... It really is a load of BS that the cab wasn't lined initially, and I'll void the warranty by doing it myself. But really, after waiting 7 months to get the cab in the first place, I'm not likely to send it back to them, only to get it back a year from now.

And thanks Seamonkey, that's a great idea but unfortunately, I don't have any extra room at the moment.

EDIT TO ADD: But I just re-read your last post Will, and you're right. I'll test it outside first and see how the vibrations are after. My guess at the moment is that the vibrations on the other items around the room are caused by the soundwaves hitting the floor, but I think the amp's vibrations are coming directly from the cab. But I will see outside before I do anything else. Thanks again.

B'Boom · #13 10-27-2011, 06:46 AM

As johnK10, I think that feet in Sorbothane are the most effective to protect circuits electronics and tube. KAB Electro Acoustics http://www.kabusa.com

crguti · #14 10-27-2011, 06:54 AM

bracing the cabinet is the cure. I started a thread about but it was buried.
I put some wood stick inside my cabinet and the vibration from the cab to the head was stopped. I'm a happy man now.

**Matthew_84** · #15 10-27-2011, 10:36 AM

Quote:

Originally Posted by crguti

bracing the cabinet is the cure. I started a thread about but it was buried.
I put some wood stick inside my cabinet and the vibration from the cab to the head was stopped. I'm a happy man now.

Yeah, it certainly did not pass the "knucke test" in my opinion anyway. So I will be bracing the cab as well as lining it.

A question about bracing though. I know to use three 1" x 1" lumber (top to bottom, side to side, and front to back), but how did you secure the braces in there? Did you glue them? Did you screw in some L brackets with 1/2" screws or something? Exactly how did you get them to stick in there?

Quote:

Originally Posted by B'Boom

As johnK10, I think that feet in Sorbothane are the most effective to protect circuits electronics and tube. KAB Electro Acoustics http://www.kabusa.com

Yeah, even though I'll be bracing and lining, I still think I should use something like this as well.

Thanks guys,
Matt

will33 · #16 10-27-2011, 10:42 AM

Cut the braces so you have to force them into place a little bit and use a healthy dose of glue. If yours are square 1x1, you can cut a little block to glue to the wall for the end of the brace to sit on. Make it easier to fit it all together and more glue surface.

**Matthew_84** · #17 10-27-2011, 10:47 AM

Quote:

Originally Posted by will33

The sealed 410 appears to have some degree of bracing but I've never seen the whole inside of one.

The cab is somewhat braced, it's not completely hollow. I'll describe it like this. Imagine you took a stop sign and cut it into four quarters (so if you were looking at the bottom-left piece, it would come come staight down for two inches, make a 45 degree cut towards the centre for about 6", and then another 45 degree cut to have it running horizontaly). These four pieces are glued to the back on the cab in the centre of all four sides bracing the back to the sides.

So it is definitely braced. However, when I do the knuckle test near the centre, top, or bottom. It is a nice high pitched sound, but as I do it in the centre of the speaker cavities (or a quarter of the way up and three quarters of the way up), it sounds very hollow.

Would adding 1x1 boards from the centre and sides and stuff really help out in this case, or should I focus on bracing right behind the speakers where the knuckle test sounds its most hollow?

**Matthew_84** · #18 10-27-2011, 10:53 AM

Quote:

Originally Posted by will33

Cut the braces so you have to force them into place a little bit and use a healthy dose of glue. If yours are square 1x1, you can cut a little block to glue to the wall for the end of the brace to sit on. Make it easier to fit it all together and more glue surface.

Ahh... Very smart! Thanks Will

will33 · #19 10-27-2011, 10:54 AM

You can use screws to help hold things together but after the glue is set, the screws are redundant so you don't need them. PL Premium construction adhesive or Gorilla Glue expands as it cures, takes up any little gaps from cutting and makes things solid. PL comes in caulk tubes you only need a little bit of, gorilla comes in little bottles but costs the same as a tube full of PL. You will find it handy to tighten up other things around the house too, loose doors, wobbly table legs, etc.

**Matthew_84** · #20 10-27-2011, 10:58 AM

K, coming up with an idea for the bracing and thinking of doing more of a tic-tac-toe grid to help out the areas behind the speakers? I will line the back wall first.

The back wall doesn't really need bracing though, I guess because of the four boards glued to it. So I won't add any additional bracing there, only on the sides.

Question though, other than additional weight, is there such a thing as over-bracing?