# How To Soundproof A Rehearsal Room

May 11, 2013February 26th, 2014No Comments

If you are going to answer the question on how to soundproof a rehearsal room, you must first define what you are rehearsing. Is it vocals or instruments? Is it one vocal or many. Is it a single instrument or a small band. You need to know the amount of energy that will be created within the rehearsal room to plan accordingly for the correct soundproof method to employ both to the inside and outside of our rehearsal room.

## How To Soundproof A Rehearsal Room – Main Considerations

Energy Assumptions

Lets first make some assumptions. Lets take a small choir, say 10 vocals and an 8 piece band. Lets use these two as our sound generating sources. These two sources will become the benchmark, so we can illustrate how to soundproof a rehearsal room. They both produce energy in similar but different parts of the frequency spectrum.

Concrete Shell

Once we know how much energy we are going to produce in the room, we can design the shell or barrier that will keep the sound generated from within our room, inside where it belongs and the noise generated from outside our rooms, outside where it belongs. A good start is concrete which will provide the barrier protection we need. We should make ours walls 8″ thick and poured concrete into molds is preferable to block. Block is a good second choice if poured concrete is not an option.

STC – Sound Transmission Loss

Sound transmission loss is the ability of a structure to reduce sound transmission from one side of the wall to the other A 8″ poured concrete wall will provide a sound class rating of 56. This means that if we have a sound source on one side of the wall that measures 90 dB, it will be 34 dB on the other side because the concrete barrier will reduce the sound pressure level by its sound transmission rating.

Dual Wood Framed Walls

if block or poured concrete is not an option, one can use a wood frame structure or rather two wood framed structures. We construct a 2″ x 4″ wall and then another 2″ x 4″ wall. We leave an air space of 4″ – 6″ whatever our physical location will permit. We isolate each wall from each other with the air space and we mechanically decouple each wall from the existing structure. This dual wall structure will afford almost the same STC value as a poured concrete wall. The poured concrete wall has a STC rating of and the dual wall has a STC rating of.

Room Size Critical

Once we have chosen our barrier configuration, we must focus on the inside of our room. If our room has been “acoustically sized” then we can begin right away with the acoustical treatment. If no thought or consideration has been given to the rehearsal room’s size then we must address that issue before we go any further. If we are rehearsing a small band then we need the correct room volume to accommodate the band’s frequency range which is a larger requirement than a vocal rehearsal room.

Room Modes

Room modes or resonances build up inside a room that is not large enough to accommodate the complete frequency range that is produced by the rehearsing source. Resonances, especially those created by lower frequencies, have no place within our rehearsal room. A microphone or band member placed in one of these modes, may not be able to hear themselves and the microphone will not be able to record the correct information because the sound needed to be recorded will be smothered by the resonances. For a small band rehearsal room make sure you have at least 30′ in one direction of the room. For a vocal room, make sure you have at least 15′ in one direction. Always choose higher ceilings for both rehearsal room sources.

Sound Absorption

Acoustical room treatment for your rehearsal room can be absorption. Low frequency absorption must be used to manage low frequency modes. It can not be foam or panels filled with building insulation. One must use tuned low frequency absorbers that can handle the low frequency energy created within room locations. Middle and high frequency absorption can be used to tame rehearsal room reflections to manage reverberation times. Make sure you choose the correct rate and level of absorption that compliments your use.

Sound Diffusion

Diffusion can be an important tool in dealing with room boundary reflections. Diffusion can take the reflected energy from the wall surfaces and spread that energy out in a fan like array in two dimensions. This spreading out of energy allows for a smoother presentation of energy at the microphone position. Two dimensions of diffusion can be achieved within your rehearsal room by using quadratic diffusion.

Variable Acoustics

Variable acoustics have gained popularity. One can have absorption panels that can be absorption on one side and diffusion on the other. An engineer can alternate between absorption and diffusion to suit the recording engineer’s acoustical palette. Portable low frequency absorbers can be rolled in to handle room resonances at certain places within the rehearsal room.