Posted by Rick Denney on February 13, 2004 at 12:04:36:
In Reply to: Soundproofing a Home Tuba Room posted by David C. Ellis on February 13, 2004 at 09:58:47:
Don't confuse reflectance with absorption. Unfaced fiberglass will limit the reflection of certain frequencies, but it will do very little to keep the sound--especially in the low frequencies--from escaping into the rest of the house.
You adjust reflectance to control how things sound inside the room. That is an entirely separate process from keep the sound from escaping the room.
Sound travels through air efficiently, but it travels through elastic solid materials even more efficiently. The only way to stop sound is to force it to travel through damped materials that absorb the energy rather than transmit it. Isolation is the key here.
The conventional construction technique for building a sound-proof wall is to stagger the studs, so that the wallboard on the inside of the room is attached to one set of studs, and the wallboard on the outside of the room is attached to a different set of studs. The studs are offset frome each other so that the wallboard and studs for the inside surface does not touch the wallboard and studs for the outside surface. This will do a lot right off the bat, but low freqencies will still get through--the two surfaces will vibrate as a result of the air between them vibrating. You control that by constraining that vibration using a damping material, such as a viscous foam between the two surfaces. You have to worry about the edges of doors and windows, too. Preferably you'll have no windows into the rest of the house. For doors, what works best is two exterior-grade metal doors with foam insulation between them, mounted so that they open apart from each other like the doors between the rooms in hotels. You'll still get sound through the doorframe, but that may not be objectionable.
If you must have a window, use two panes of glass, with one slanted from the other so that they are not parallel. This is how radio and TV stations build windows into sound studios.
You can do all this and still leave the interior surfaces of the room with a hard surface, so that it has as much interior reverberation as you want. Lots of people line their walls with reflection-control material like Sonex, which does not provide soundproofing, but which does make the room sound dead and tubby when you play in it. This is my beef with the Wenger practice rooms.
10' x 12' with an 8' ceiling will not provide a lot of reverberation, so I would leave the walls hard-surfaced to the extent possible. But I'd kill echo without killing reverberation by setting up panels along the walls that eliminate opposing parallel surfaces. If you can open up the ceiling at all, do so, and an irregular ceiling surface will kill the echo with the floor. But don't forget that soundproofing might be a problem through the ceiling, too. If you have rooms above the practice area or a common attic with other rooms, you have to build an isolation ceiling similarly to the isolation walls to stop that sound. Likewise floors.
Rick "who once had complaining neighbors but who now lives in the country" Denney