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Theory / custom practices for sand filled stage construction (?)

post #1 of 10
12/26/12 at 11:28pm
Thread Starter 
First, I'll start off apologizing if this already exists somewhere, I haven't found it with the search, but my keywords may have been flawed. Have asked about it a couple of times with no pointers either.

So, I'll start this and see if someone will redirect me, or else start gathering information here.

Two things have been playing on my mind and they both are "decoupling" issues. I believe in the examples I've seen that the upper floor part of the stage has been anchored to the frame (is that so?). In that case - should anything special be done to decouple it from the floor - rubber mat or something like that, or is the pure weight and sand contents enough to prevent any transmission through the wood parts?

The second thought I've been having is if one couldn't bring the sand more into play by building the floor part in such a way that it is floating on the sand rather than being connected to the frame?

Do we have any stage experts around? (Or can someone point me to a thread where all this has been dealt with before?)
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post #2 of 10
12/27/12 at 12:07am
Have a look at this thread - http://www.avsforum.com/t/1048045/acoustic-properties-of-sand
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post #3 of 10
12/27/12 at 12:21am
Thread Starter 
Thanks Elill, that answers some of it.

Another question could be - how high does it have to be to be useful? Would say... 4 inches be enough? 6 ?
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post #4 of 10
12/27/12 at 12:46am
Thats a question for Big.....I'd check out some of his recent build threads - http://www.avsforum.com/u/60657/BIGmouthinDC

Scroll down to the bottom to his signature, there are about 4-5 with lots of really good info
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post #5 of 10
12/27/12 at 6:08am
I think you may be over analysing the situation. First you build the stage such that framing is spaced away from any walls to eliminate that source of vibration transfer, you fill it to the brim with sand and pack it down. You cover with 2-3 layers of decking. Three layers of 5/8 OSB works well. Put green glue between layers. Carpet. Floating the frame on resilient pad would be defeated by the weight but might have a good placebo effect. I use roofing felt to help the frame sit more securely to the concrete floor, If building on a subfllor over concrete none is needed.

Floating the top of the stage on the sand and not attaching to framing is IMHO just a bad case of OCD.

If you are building the stage on floor joists over other parts of the house or crawl space then sand may not be a good choice because of the weight. You can fill a few sections directly under the sub for a partial benefit.
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post #6 of 10
12/27/12 at 6:53am
Thread Starter 
Quote:
Originally Posted by BIGmouthinDC View Post

I think you may be over analysing the situation. First you build the stage such that framing is spaced away from any walls to eliminate that source of vibration transfer, you fill it to the brim with sand and pack it down. You cover with 2-3 layers of decking. Three layers of 5/8 OSB works well. Put green glue between layers. Carpet. Floating the frame on resilient pad would be defeated by the weight but might have a good placebo effect. I use roofing felt to help the frame sit more securely to the concrete floor, If building on a subfllor over concrete none is needed.

Concrete. I'll be using weight-matched soft feet for the speakers, I assume that will do just as well or better than carpet. I don't intend to show off the stage so I don't need to carpet it for visual purpose.

3 times 5/8 = 15/8? That's something like 5cm.... that's massive. How about MDF, would that be just as think?
Quote:
Floating the top of the stage on the sand and not attaching to framing is IMHO just a bad case of OCD.

biggrin.gif I was just thinking of making sure the sand got some action. wink.gif

BTW, has anyone tested building a stage like this without sand to determine if it has the desired contribution? Or compared it to putting the speakers directly on the concrete (on soft feet) ?
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If you are building the stage on floor joists over other parts of the house or crawl space then sand may not be a good choice because of the weight. You can fill a few sections directly under the sub for a partial benefit.

Ok, but that would be about all of it anyway - it will be two stacked at each front corner and two in some manner in the middle.
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post #7 of 10
4/7/13 at 8:40am
OK, BIG I have built my stage (6" high) and I have 3/4" plywood on top for now. I only have enough room to add another 3/8-1/2" at most and can put GG between the layers. Is this necessary or rather what benefit do I get (if any) from adding this extra layer?

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post #8 of 10
4/7/13 at 10:29am
When you stomp your feet now on the stage how does it sound? There will be some difference if you add a 1/2 inch layer with GG. Will you you be able to hear it? , hard to tell. It is one of those things that you aren't going to take up the carpet and redo at a later date. So if you already have the Green Glue on hand I would just do it. Just like you accepted the fact that you needed the sand.
Edited by BIGmouthinDC - 4/19/13 at 4:57am
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post #9 of 10
4/18/13 at 8:46pm
Thanks as always, BIG
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post #10 of 10
4/20/13 at 1:17am
There's more to the carpet than aesthetics. Lots of frequencies bouncing around back there. Unless you treat the ceiling, I would recommend carpeting the entire stage.
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