how to make a transparent soundproof box

August 11, 2006 2:00 PM

What are the best materials for making a transparent soundproof box?

I'm trying to construct a large soundproof cube, with an edge of, say, two feet. It's for an art idea. I was thinking plexiglass attached with screws and sealed with epoxy. What minimum thickness of plexiglass would I need and is that the best way to seal/soundproof it? And what's the best way to cut plexiglass? (I'm a total newbie when it comes to tools.)

An additional issue is that I would need to drill a hole so that a cable could go into the cube, but I need to soundproof that opening as well. Should I simply coat the interior of the hole with epoxy, which will hopefully prevent sound leakage while simultaneously preventing the cable from slipping in and out?

posted by ObeyScient to media & arts (16 comments total)

Before you spend a lot of money, remember that you'll never really be able to soundproof something like that.

Soundproofing involves mass and dead air. Plexiglass is not likely to provide enough of either.
posted by jon_kill at 2:04 PM on August 11, 2006

Maybe a plexiglass cube inside a plexiglass cube? The air (or vacuum, if you could swing it) between the two should create some kind of sound buffer. But jon-kill's right, you're never going to get a perfectly soundproof box with plexiglass an epoxy.
posted by Terminal Verbosity at 2:12 PM on August 11, 2006

"...plexiglass and epoxy," obviously.
posted by Terminal Verbosity at 2:15 PM on August 11, 2006

I absolutely support Terminal Velocity- use vacuum to prevent sound transmission, buy the thickest acrylic/plexi you can afford, make the void between the cubes as large as possible, and construct with epoxy. I've done a number of projects like this for a movie sound studio, and they're tough. Use closed-cell foam and rubber to seal the cable hole.
posted by wzcx at 2:22 PM on August 11, 2006

When (if) you do the double cube approach, make one cube out of a different thickness of plex than the other. Acoustical consultants that I work with tell me this works (for more than just plex cubes, natch). It blocks a wider spectrum of sound than using the same thickness everywhere.
posted by misterbrandt at 2:28 PM on August 11, 2006

A vacuum between two cubes would be great in terms of soundproofing. The best way would be to support the internal cube with magnets, therefore eliminating mechanical transmission of sound. Making a hole for a cable vacuum-proof may be tricky though, and also you would have to build a connection for a vacuum pump. (Also not impossible)

Your plexiglass will have to withstand a force of 15psi of course, and make sure the center doesnt flex too much pulling your glued edges apart...

Another thing. This is an art installation right? Is there a way you can pretend it's a soundproof box, by turning off the speaker while the box is closed? I mean, it's soundproof, so if you hear nothing, it must work right? Embed a microswitch in the right place, and the sound would come back on while opened? (Or drop the volume substantially, so it's almost soundproof, but you can hear a whisper?)
posted by defcom1 at 2:37 PM on August 11, 2006

If your budget does not allow for sending it to a machine shop for cutting you can do it on a bandsaw, make a few practice cuts and lay out lines to follow. This will be kind of rough and even if you have skills it will be at least .050 out of flat along the edge, this stuff files pretty easy and the epoxy will help to mask the roughness. When you drill drill .020 under your finished hole size and then finish drill. On both drilling pass's make a real effort not to push too hard, maintain a controlled downfeed to avoid chipping. The second pass is for a better finish as the first will leave a rough melted surface in the hole.
posted by Iron Rat at 2:41 PM on August 11, 2006

You can use a dremel for cutting... They have cutting wheels or big-based cutters that cut through plexiglas very quickly. You'll still need a way to mount the dremel, and a good sized table to do all of the cutting.
posted by hatsix at 3:55 PM on August 11, 2006

A vacuum would probably work. Sound will still travel through the material supporting the inner cube, so make it tough. I would suspend the inner cube by thread. Use the thinnest wire possible for your cable. Wirewrap wire would be ideal. Seal the hole with epoxy. You will need some sort of valve on the cube to allow attachment of a vacuum pump and then seal in the vacuum. Perhaps it can be hidden in the support or some other feature of the work.

Cut the plexiglass on a table or radial arm saw with a fine blade and something attached to the faces of the plexiglass during the cut to protect them from scratches. You will want to get a good straight edge and that is what these tools are designed for. You might be able to get a millwork shop to cut it for you for a small fee.
posted by caddis at 3:57 PM on August 11, 2006

Lookup resources on constructing clear plexiglass computer cases, there's excellent advice all over the net from obtaining plexiglass to measuring and cutting the plexiglass to making your own plexiglass-based clear glue.
posted by crunchyk9 at 4:01 PM on August 11, 2006

Thanks, everyone, for the suggestions.

defcom1, I did consider whether I could just pretend it's soundproof by turning off the sound. The concept involves people thinking that the box is indeed soundproof (thus allowing the assumption that there is sound). What I'm getting from y'all is that a single box may not even *look* soundproof to knowledgeable folks--leading people to wonder if the volume is just turned off. While the concept might be enhanced if people then wonder if there actually is any sound inside, that wasn't the original point...

...although that might make an excellent sister exhibit!
posted by ObeyScient at 4:56 PM on August 11, 2006

A vacuum would work really well, but there's no way you're going to seal it well enough for a vacuum to sustain for very long (i.e. more than a minute or so). Making something like that tight is a real pain. You'd need to maintain a pressure below about 20 torr, I would think, and that's really hard for a garage-shop project. At 100 torr you're not going to be soundproof any longer.
posted by Steven C. Den Beste at 5:56 PM on August 11, 2006

If you are going to pull a vacuum use Lexan instead of plexi in case of failure. Plexi shatters into all sorts of big, nasty, sharp shards; Lexan doesn't.

One thing that would make your sealing job easier is to make the box out of two rectangular sheets X wide and 3X long where X is the desired final size of your cube. Then bend the sheets using heat into a squared off U shape. The two Us will fit together to form your box (like the casing on a baseball) and you'll have reduced the number of joints by 4.
posted by Mitheral at 6:39 PM on August 11, 2006

What I'm getting from y'all is that a single box may not even *look* soundproof

Even a single box would be pretty soundproof with no media inside through which to transmit the sound. Pull a vacuum on it. However, without the media I am not sure you could really say that any sound was being produced. If a tree fell in a vacuum, . . . ?
posted by caddis at 9:50 PM on August 11, 2006

Also, designing a pressure vessel to withstand an external pressure of 15 psi is no big deal. Just make good glue joints and all will be well. The real issue is getting a pump which will be able to pull a pretty good vacuum. You may very well remember a grammar or high school experiment in which your teacher placed an alarm clock into a bell jar and let it go off first with no vacuum (loud but slightly muffled by the glass of the jar) and then under vacuum (essentially silent). Those vacuum pumps could not be that powerful or expensive. Find something like that and you will be golden.
posted by caddis at 10:06 PM on August 11, 2006

Use Armor All as a cutting fluid, spray your drill bit, saw blade,
and you won't melt the plexie.
posted by hortense at 11:30 PM on August 11, 2006