10 important facts about acoustics for microphone users
By audio specialist Eddy B. Brixen
- Reverberation – The time it takes the sound to die after the sound source has stopped. “A dry room” has a short reverberation time and “a wet room” has a long reverberation time. Depending on the use of a room an optimal reverberation time exist. A control room is typical below 0.4 sec. A concert hall for symphonic music typically around 2.2 sec.
- Sound insulation – The sound reduction from one room to another. Good insulation is obtained by using heavy materials and by avoiding/minimizing building parts in each room to have rigid connections.
- Absorption – In acoustics a property of a material. Absorbing material converts sound energy. The absorption of a given material varies with frequency. Some materials have a high absorption at high frequencies, other at low frequencies or perhaps at medium frequencies.
- Reflections – Hard and thus not absorbing, surfaces reflect sound. Reflections are the reason for reverberation. In large rooms, the reflections may provide sound distribution and the perception of spaciousness. Strong single reflections can, however, result in colouration of the sound.
- Diffusion/scattering – The spread of reflected sound. Absorption or diffusion can remove reflections. However, in contrast to absorption, diffusion keeps the sound energy in the room.
- Standing Waves– Waves that fit into the room dimensions can affect the distribution of the sound. All rooms have standing waves.
- Room size – The room size influences the sound of your recording. Larger rooms also have higher reverberation time. Too small rooms like speak-boxes may sound too boxy.
- Background noise – The unwanted noise from installations, outdoor traffic, etc. In good rooms for audio, this noise should be kept as low as possible.
- Mechanical vibrations – Mechanical vibrations may eventually end up as sound in the microphone. This is why it is recommended to apply mechanical damping of microphones.
- Headphones – Important tool in many forms of audio production. The sound level should never be so high that the microphone catches it.