How to construct a stage platform to reduce footstep noise / bass?
July 21, 2015 5:44 PM   Subscribe

Historically I have not been an incredibly handy person, but I currently find myself in the process of DIY building a few modular stage platforms from 2x4s and 3/4" plywood which will be clamped together to serve as a stage for a blackbox theatre space that I run (used for improv, sketch and stand-up comedy). Does anyone have any construction tips or recommendations to dampen the noise from footsteps?

Currently the platforms are structurally sound, but I'm unhappy with the amount of noise they produce when walked upon. When there are multiple people on stage moving at the same time, it's like each platform is a bass drum that kicks whenever someone takes a step. As the room itself is already prone to echoes, this isn't ideal acoustically.

I've built the platforms following these instructions. I'm considering adding two extra 3'9" support beams to each frame to really make sure they're stable and reduce the size of each "drum cavity".

Note that I have *not* put the legs on and added skirting to the platforms yet, so I have yet to determine how being raised off of the ground will affect the acoustics. My guess is that raising them off the ground will help somewhat as the geometry will be less drum-like with open air under the platforms. This might be a major part of the solution, and I'm putting too much importance on the flooring materials. Any thoughts there?

As for adding additional flooring materials on top of the plywood, I've read a few different articles with a few different suggestions for damping (e.g. adding a thin layer of foam or cloth above the ply, and then a thin layer of hardwood or A-grade ply on top of that).

I'd like the final product to be black, and I plan to paint once construction is done.

Any thoughts, advice or anecdotes would be appreciated. I'd like to hear the performers' voices, not their feet!
posted by adamk to Media & Arts (10 answers total)
Yes, add two more 3'9" supports for stability.
This type of platform is usually built with two center supports. You can build them with one, but they aren't as sturdy this way, and they will sometimes flex visibly when stepped on. Two is better, more rigid.
The platforms will be much quieter once they are in the air. You can staple carpet scraps or egg crate padding to the underside to further deaden noise. Your layering plan will also probably work fine, but be more expensive. Which, hey, if you've got the money to spend, more power to you!
posted by Adridne at 6:03 PM on July 21, 2015

Hmm... I'll ask my brother, who basically builds stages for a living, but I'd staple old carpet upside down on the top board, or foam like you said, or some other material, and then put another board on top of that. I'd probably cover it with a later of something too, maybe rubber.
posted by gryftir at 6:08 PM on July 21, 2015

Sound bounces off hard surfaces. You want to have something disrupting the sound bounce. You have two big surfaces here - the stage and the floor. Cheap carpet remnants stapled to the bottom of the stage and one on the floor would make a huge difference.
posted by 26.2 at 6:09 PM on July 21, 2015

Once you get the platforms up, make sure they are all clamped or bolted with each other as well (big old metal c-clamps are great for this.) In my experience, a stage that's more like one big unit will be less wobbly and noisy than a small one.

The 6 legs given in the tutorial are good, but you could also add another leg right in the middle of the platform. More of the 3'-9" bracings should help as well. I like the plan above to have 2 cross braces (one every 2.6 feet, rather than one every 4)

Make sure you don't have any wobbly or short legs -- they'll give you a "clunk" of a different but still annoying kind.

I've used Sound Deadening Board (usually used for walls) as part of a layered stage floor in the past -- If you can find it near you, it might help. Could then deck that with a layer of Masonite to get the smooth and paintable floor back.
posted by Wulfhere at 6:10 PM on July 21, 2015

Carpet on the top, Fiberglass insulation on the bottom.

My guess is that raising them off the ground will help somewhat as the geometry will be less drum-like with open air under the platforms.

Hard to say - you might just wind up changing the frequency (pitch) of the drum sound.
posted by soundguy99 at 6:41 PM on July 21, 2015

Spend $20 on a two pack of Boom Mat, stick it to the underside, and see how it attenuates the noise. If it works, get enough to finish your project. (Keep in mind 100% coverage isn't necessary.) If not, you're only out $20.
posted by ob1quixote at 7:23 PM on July 21, 2015

From my brother, who has a degree in Technical Theater and builds stages professionally, based on what I told him I was going to suggest.

"Does the top layer need to be wood? If not adding carpet padding and carpet is a cheap way to go. The theater solution is typically to put homasote on top of the plywood and then a thin top layer like 1/4" duron Masonite. This deadens the sound but still gives a solid walking surface. "
posted by gryftir at 9:34 PM on July 21, 2015 [1 favorite]

Another type of sound deadening board you can use is Soundstop for the floor of your platform.
posted by Deflagro at 10:09 PM on July 21, 2015

I've built a lot of home studios and rehearsal spaces, and I've found the best way to approach the problem is to understand that the best way to amplify the sound and make it travel as far as possible is to use materials that are as rigid and lightweight as possible. The best resonator would be infinitely rigid and have zero mass.

So basically, you want to do the opposite and make your stage as heavy and soft as possible. If you won't be moving the stage, the simple solution is to seal it up and fill it with playground sand. Works amazingly well and cheap.

If you are going to be moving the stage, or setting it up and tearing it down a lot, you may find the sand adds too much weight. In that case the first thing I would focus on isolating the individual sections of the stage from each other and from the floor. Heavy rubber is the best choice for this. You can get it for free in the form of worn tire treads from a used tire shop. It'll take a bit of work to cut it all to shape and screw it into place, but new rubber gets expensive quick (see Dynamat), so it's probably worth it.

You want rubber to rubber contact between each section of the stage where they meet each other, and the floor. It's also a good idea to add some rubber to the bottom of the stage on the inside to damp footsteps. Your goal with the underside of the stage is to add mass, so 3 layers affixed to the center of the panel will do more for you than complete coverage.
posted by Anoplura at 10:30 PM on July 21, 2015

...Couple of other notes, just in case:

1. In my experience, DIY materials can achieve much better results than commercial sound-deadening solutions*. But that assumes you have experience and know what you are doing. There are a lot of "sound-proofing" solutions that are serious fire hazards. (I'm looking at you, eggcrate foam and carpet remnants on the walls) You can get in a lot of trouble trying to DIY it inside the theater space itself or in any other public space.

2. If you end up doing the used tire tread thing, please use a utility knife or other sharp blade to cut the rubber. Power tools or a serrated blade (hacksaw ect) will leave you with a mess of rubber dust that is very bad for your lungs.

*I believe the main reason for this is that adding mass (weight) is more effective add damping sound than simply adding soft surfaces, but that shipping heavy, acoustically effective solutions is prohibitively expensive.
posted by Anoplura at 10:53 PM on July 21, 2015

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