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post #31 of 55 Old 12-31-2011, 08:35 AM
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I recently built a stage and riser for a client both with three layers of 5/8 OSB with green glue (A Dennis Erskine design). The stage had sand and the riser had insulation. There was a definite difference walking and thumping on the stage versus riser. If you are going to place beefy subs on the stage, use sand it will help dampen vibrations that the subs will want to send through the floor to the rest of the house. I hate carrying sand down flights of stairs but it is worth the effort.
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post #32 of 55 Old 01-02-2012, 04:57 AM
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Quote:
Originally Posted by Kensmith48 View Post

I don't know why sand is used. I put some sand under my stage (approx. 3-4 sq. ft.) and then I decided on insulation. I packed alot of fiberglass insulation inside my stage and I don't have any problems. I have 2 subs on it and I can't tell the difference between that and where the sand is.

Dennis has chimed in before (in BritinVA's thread) that those little sections don't have enough mass to make a difference. As to the why, I have pulled this quote out a few times:

Here is what I pulled together in another thread:

[quote]
Quote:
Originally Posted by Jet Captain View Post

Dennis Erskine, uses insulation in upper floor builds and I am sure it doesn't hurt your room, just doesn't help as much. I was just reading his posts on the topic yesterday, and this is his discussion of what you are giving up. Makes me almost want to put one in my next build, even though I am not sure I have the room. Here is the quote:

Quote:
Originally Posted by Dennis Erskine View Post

The sand filled stage is a functional portion of a good home theater which, fortunately, can be disguised as something architectural and belonging in the room (such as stage, for example). First, the stage must be constructed AFTER the drywall is installed. Second, when it is built, it should not come into contact with any of the walls (and idealy be isolated from the floor or that great sound conductor called a concrete slab). Here's what it does:
1. the subs are anchored to the stage. For optimal subwoofer performance, the sub must be anchored to something of considerably more mass than the sub itself.
2. The dry play sand provides the mass; but, it is not a solid mass that would allow vibrations from the sub (and the other main speakers) to pass through on their merry way to the rest of the house...the sand is an absorber reducing (rather dramatically) the amount of kinetic energy entering the structure.
3. Because the kinetic energy is not being transferred to the structure, your walls do not become occasional speakers injecting distortion artifacts into the room.

[At the lower frequencies, the vibration enters the structure...within the home their a lots of walls of different sizes, shapes and mass. Each of this has a resonance frequency. When that resonance frequency is equal to or a harmonic of the frequency being produced by your sub, that wall becomes a speaker...and, a surprisingly loud one at that.]

Here's another POV. You're spending a bunch of money on your gear (and many times a few grand on your subwoofer). For $300 to $500 are you willing to bet it (the stage) won't help.

Until you've heard truly smooth bass response and the sound in a well calibrated room, you cannot imagine what you're giving up...and, I've a demo room for just that purpose.

EDIT - and check out this thread for some good build diagrams.

http://archive2.avsforum.com/avs-vb/...&&#post8162230

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post #33 of 55 Old 01-02-2012, 07:47 AM
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You guys can haul sand in your basement if you want to do more work than necessary, but insulation did the job in my basement. I,m also wondering why we build stages. When the speakers are on the stage aren't the tweeters too high? I thought they should be at ear height when sitting.
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post #34 of 55 Old 04-30-2013, 05:34 PM
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An ancillary question as I get ready to order sand from the supply yard....

 

Assuming one thinks it is a reasonable thing to line the stage-filled-with-sand with a poly liner of some sort, would it make any difference on how one used the poly?

 

1) lay down poly before the stage is framed and then frame the stage as is typical.  This would leave you with one big "tub" of poly with a bunch of 2 by's crossing over the poly comprising the rest of the structure of the stage.  The poly would be nailed through the end caps of the stage where the perimeter of the stage framing is secured to the "interior" stage framing.  Then sand is put into the big tub section by section and then screeded.  Any excess poly around the perimeter could be folded over the framing members and then the top put on as per typical.

 

or

 

2) frame the whole stage first and then lay the poly up and over each framing member sequentially leaving a "wavy" layer of poly the goes to the floor, up and over a framing member, back down the the floor, up and over the next framing member, etc.  Then sand would be used to fill each "cavity" sequentially.

 

I guess the main difference would be whether sand in contact with the framing members is a good thing or a bad thing and whether there is any concerns about the poly being fragile enough to rip or tear with all that weaving up and down or whether the weaving causes any issues with filling the cavities.

 

I'd be interested in hearing peoples' thoughts on this one.


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post #35 of 55 Old 04-30-2013, 08:41 PM
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I've been lining each well independently and trimming at the top, not up and over. Fill each well 2/3 full and pack into the corners then trim the plastic. Then fill the remaining space and level with a straight board.
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post #36 of 55 Old 05-01-2013, 01:03 PM
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I suspect that all methods would function identically, but one way may be easier, less messy, or have less chance of problems?


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post #37 of 55 Old 05-01-2013, 07:11 PM
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I found the same thing that Logan did with Home Depot storing at least some of their sand outside and Lowes inside.

What calculation should I use to determine how much sand to get? I have seen 100lb=1cubic foot. Is this accurate? It gets a little tricky when you have a curved stage though.

And the best way to vibrate the stage to settle the sand........is the recipro saw without blade the best way to go?
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post #38 of 55 Old 05-02-2013, 02:32 AM
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Quote:
Originally Posted by BIGmouthinDC View Post

I've been lining each well independently and trimming at the top, not up and over. Fill each well 2/3 full and pack into the corners then trim the plastic. Then fill the remaining space and level with a straight board.

With all the vibration, wouldn't sand ever leak out of the stage? Potentially into the room? Sorry if this is a dumb question...
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post #39 of 55 Old 05-02-2013, 06:01 AM
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Sand does not act like jumping beans amigo. the top is screwed down tight, it's never been a problem. If your OCD meter is always reading 10 and you wake up at night concerned that the sand is escaping while you are not looking in an effort to make it back to some beach, you put a bead of caulk on the top edge of the stage framing before screwing down the cover and another under the front lip before the carpet goes on.
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post #40 of 55 Old 05-02-2013, 09:33 AM
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Quote:
Originally Posted by jedimastergrant View Post

What calculation should I use to determine how much sand to get? I have seen 100lb=1cubic foot. Is this accurate?

Anyone know if this is correct?
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post #41 of 55 Old 05-02-2013, 12:52 PM
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post #42 of 55 Old 05-02-2013, 12:53 PM
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post #43 of 55 Old 05-02-2013, 02:13 PM
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Just a thought too --

But make sure the sand is DRY. Frequently even bagged sand is somewhat moist.

When I filled my stage I had to let it dry out for about a week while running a dehumidier..and these were sealed bags without holes/leaks. The last thing you want is to enclose moist/wet sand in your stage.

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post #44 of 55 Old 05-02-2013, 07:03 PM
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Quote:
Originally Posted by Kensmith48 View Post

You guys can haul sand in your basement if you want to do more work than necessary, but insulation did the job in my basement. I,m also wondering why we build stages. When the speakers are on the stage aren't the tweeters too high? I thought they should be at ear height when sitting.
If you don't have a riser, than the tweeters might be too high, but most of us have risers for a 2nd or 3rd row of seats. In those cases, the tweeters height is a compromise that good equipment can take care of (Audyssey).

As for sand vs. insulation, I'm glad the insulation worked for you. I helped a buddy build a theater after he saw mine and he wanted to forgo the sand. We filled his stage with insulation instead and when it was all buttoned up, it resonated like crazy. He ended up moving his sub to another section of the room, so things worked out, but after "hearing" that, I always recommend sand.

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post #45 of 55 Old 05-03-2013, 08:49 AM
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Quote:
Originally Posted by BIGmouthinDC View Post

Sand dies not act like jumping beans amigo. the top is screwed down tight, it's never been a problem. If your OCD meter is always reading 10 and you wake up at night concerned that the sand is escaping while you are not looking in an effort to make it back to some beach, you put a bead of caulk on the top edge of the stage framing before screwing down the cover and another under the front lip before the carpet goes on.

a lil cantankerous today, eh? smile.gif

thanks for the info/advice
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post #46 of 55 Old 05-03-2013, 08:51 AM
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Dry Sand?

That warning comes up a lot in this area but let's think this out a bit more. First I would not advocate putting wet sand in a riser but it doesn't need to be bone dry either. First the construction lumber has a high moisture content and has to be sold that way by code I was told. So a bit of additional moisture from some not completely dry sand is not going to make it that much worse at all.

If the sand is moist, it will dry over days or weeks through evaporation though the wood. Here, the plastic is actually a hindrance. Now if your slab is dry, how is the sand ever going to get moist again? If you have a slab moisture problem, that sand will get wet no matter how dry it is when poured in. And it will stay moist too.

So IMO, it's all about the concrete moisture. If your slab is dry, the sand will dry out on it's own and stay dry. If you have slab moisture, you need to fix that because your "bone dry" sand will be wet again within a day or two.

If you are building on a second floor, moist sand is really not an issue at all. So yes, dry out your sand but don't go crazy over it. A little moisture left in the sand is not a problem.

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post #47 of 55 Old 05-03-2013, 09:15 AM
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Quote:
Originally Posted by Kensmith48 View Post

You guys can haul sand in your basement if you want to do more work than necessary, but insulation did the job in my basement. I,m also wondering why we build stages. When the speakers are on the stage aren't the tweeters too high? I thought they should be at ear height when sitting.

At least in my case, just because I liked the look, and nothing else. Since I'm not using tower speakers, the speaker height has to be adjusted up regardless of whether the stage was there or not.
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post #48 of 55 Old 05-17-2013, 01:10 PM
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Sand does exactly what ? What is the purpose over say.. just stuffing with traditional pink insulation ??

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post #49 of 55 Old 05-17-2013, 01:20 PM
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Originally Posted by Mfusick View Post

Sand does exactly what ? What is the purpose over say.. just stuffing with traditional pink insulation ??

Sand = major mass and some damping. The goal is to prevent vibration from subwoofers and speakers on the platform from transmitting that vibration through the riser structure into the subfloor below, creating a flanking path for sound to escape from your theater. It also eliminates any possible hollow "drum" sound if the cavities were left unfilled.

Or as Dennis Erskine explains it in a previous post in this very thread: http://www.avsforum.com/t/1379811/how-to-fill-a-stage-with-sand/30#post_21429312
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post #50 of 55 Old 05-17-2013, 01:26 PM
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In these sand filled stages is the top surface that the subs rest on floating on the sand? Or is it screwed down to pieces of dimensional lumber that are then fixed to the subfloor? Is there a design drawing around that someone can point me to?

edit: looked on first page and found drawing

Doesn't the sub vibration just go straight into the subfloor?

The top of this stage is very stiff (3 layers of OSB) and there is a hard mechanical connection to the floor via the dimensional lumber used for stage framing. The whole structure is very stout and will resist vibration. Any vibration from the sub is pretty much coupled straight into the floor.

Wouldn't it be better to decouple the sub? Put it on some isolation mounts, float it on acoustical foam or fiberglass? If you used sand surely it would be better to sit the sub straight on the sand or on a small piece of wood touching only the sand and nothing else e.g. http://www.cognitivevent.com/sandbox.html

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post #51 of 55 Old 05-17-2013, 02:10 PM
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Quote:
Originally Posted by Nyal Mellor View Post

In these sand filled stages is the top surface that the subs rest on floating on the sand? Or is it screwed down to pieces of dimensional lumber that are then fixed to the subfloor? Is there a design drawing around that someone can point me to?

edit: looked on first page and found drawing

Doesn't the sub vibration just go straight into the subfloor?

The top of this stage is very stiff (3 layers of OSB) and there is a hard mechanical connection to the floor via the dimensional lumber used for stage framing. The whole structure is very stout and will resist vibration. Any vibration from the sub is pretty much coupled straight into the floor.

Wouldn't it be better to decouple the sub? Put it on some isolation mounts, float it on acoustical foam or fiberglass? If you used sand surely it would be better to sit the sub straight on the sand or on a small piece of wood touching only the sand and nothing else e.g. http://www.cognitivevent.com/sandbox.html

The recommendation is that these top layers of material have Green Glue in between them for a constrained layer damping system, so two layers of Green Glue in a 3-layer OSB top platform.

I haven't previously seen where they used sheets of polycarbonate sitting directly on sand on top of a substrate on top of... (gulp) ... raquetballs...lol! tongue.gif I am sure it works, but definitely not convenient for normal construction methods. I like the use of isolation mounts and platforms to place the speakers / speaker stands and subwoofers on as a first line of defense against vibration getting into the riser, but it's also smart money to fill the cavities with the cheap mass of play sand, don't you think? Not mentioned, but a lot of folks build these risers on 3/8" Serenity mats to decouple and dampen the entire platform structure.

http://www.avsforum.com/t/1379811/how-to-fill-a-stage-with-sand/30#post_21429312
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post #52 of 55 Old 05-17-2013, 02:21 PM
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Well assuming sound escaping the theater isn't an issue at all...

Is there other benefits like better sound quality inside the theater?

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post #53 of 55 Old 05-17-2013, 02:43 PM
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It's not an acoustic treatment, just limiting the impact it can have. Of course it can have slight acoustic differences depending on the finish material (wood, padded carpet), but not really the highest priority in the room, acoustically speaking. Refer here in this thread: http://www.avsforum.com/t/1379811/how-to-fill-a-stage-with-sand/30#post_21429312
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post #54 of 55 Old 05-17-2013, 05:18 PM
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Thanks !

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post #55 of 55 Old 05-17-2013, 05:55 PM
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Quote:
Originally Posted by TMcG View Post

The recommendation is that these top layers of material have Green Glue in between them for a constrained layer damping system, so two layers of Green Glue in a 3-layer OSB top platform.

I haven't previously seen where they used sheets of polycarbonate sitting directly on sand on top of a substrate on top of... (gulp) ... raquetballs...lol! tongue.gif I am sure it works, but definitely not convenient for normal construction methods. I like the use of isolation mounts and platforms to place the speakers / speaker stands and subwoofers on as a first line of defense against vibration getting into the riser, but it's also smart money to fill the cavities with the cheap mass of play sand, don't you think? Not mentioned, but a lot of folks build these risers on 3/8" Serenity mats to decouple and dampen the entire platform structure.

http://www.avsforum.com/t/1379811/how-to-fill-a-stage-with-sand/30#post_21429312

Well yes the GG will stop the OSB vibrating at a particular frequency and absorb some energy. Adding mass via sand will lower the resonant frequency of the whole caboodle and I guess the sand also has some natural self damping. All this will basically stop the structure you have just created from resonating. There is still the hard connection to the floor, but breaking that with a serenity mat will add some decoupling.

Is there any evidence out there of the benefit of this structure? An experiment should not be difficult to pull together, maybe using the same measurement equipment used to measure loudspeaker cabinet vibrations.

Test 1) sub on serenity mat on floor
Test 2) sub on sand filled stage on mat on floor

Look at resonance in the floor structure and compare. Best waterfall plot wins.

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