# sand calculation

#### corona13

##### Stunt Coordinator
completed the framing of my stage. Planning on filling the stage with sand as my subwoffers will sit on the stage.

How does one calculate the amount of sand to purchase.

I assume you must calculate the volume of each area to fill, but need some help here.

stage is 2.5 feet wide X 13.5 long with standard 16 inch oc studs. height is 3inches (used standard 2x4s)

#### Jeff Gatie

Senior HTF Member
7.5 cubic feet should do it.

You have a (2.5 * 13.5 * .25) total area = 8.4 cu.ft.
Minus the studs (.25 * 2.5 * .125) = .078 * 11 studs total (~13.5 / 1.3 + 1) = .858

8.4 cu.ft. - .858 cu.ft. = 7.52, round it to 7.5 cu ft.

#### corona13

##### Stunt Coordinator
thank you very much!

#### Jeff Gatie

Senior HTF Member

No problem. Gives us geeks a purpose in life.

#### slide90

##### Auditioning
I'm a bit of a novice at this. Could you explain the purpose of using sand in your platform?

#### BruceSpielbauer

##### Second Unit

If left empty, you may end up with the largest bass drum you have ever dealt with, a big empty hollow structure which reverberates horribly every time the subwoofer kicks in, and amplifies that low frequency "thoomp" to the point where it reverberates and echoes and overlaps all other sounds for an unnatural period of time after its sound should have ceased altogether. That structure will have its own frequency, and when the subwoofer kicks out that same frequency, watch out! Each framing member is also likely to have its own frequency, as well. Ditto.

Many subwoofers end up on top of that stage, or even in that stage, which can make this problem even more pronounced.

Sand is a reasonably inexpensive means of solving that problem. Some have tried just using bats of insulation, and similar tricks, but still experienced issues.

There are a few lesser reasons, as well.

-Bruce

#### PeterK

##### Supporting Actor
so this is on the front stage that you would use to put like a tv and ur speakers on? so you fill the entire thing with sand? do you line it with something first, or just start pouring sand into your room?
would the same thing go for seating stages? or a raised theatre floor?

#### BruceSpielbauer

##### Second Unit
It is becoming very common to fill the front stage with sand. Dry sand. Typically, the same stuff that is used in sandboxes, but it is very important that it be as dry as possible when it is poured.

Most people line each cavit between the framing members with some sort of plastic liner, and then pour the sand into that. If speakers will be sittin on top of that stage, this can be important. If one of those speakers will be a subwoofer, this becomes even more important.

As for the seating platform or riser, this is usually not as critical. However, it is still important to fill it with something. I am using regular fiberglass insulation. Again, the purpose is to avoid ending up with a huge hollow structure which will pick up certain frequencies and re-amplify them, or reverberate them. The hollowness of such a wooden structure could make it a very very large musical instrument, one which might completely change the acoustics in the room, and probably not for the better.

Below is a link to a page at Ted White's excellent website, which discusses this:

Here is a link to one guy's stage:

http://www.cinemawizards.com/photos/StageSand.jpg

Here is a link to another guy's stage. On this page, you need to scroll down a ways:

-Bruce