My Home Studio - Construction and Design

Conclusions From Initial Research

For acoustic music, I want a partially live room, not as dead as some pop multi-track studios. At the same time, my room is on the small side, not really large enough, nor shaped optimally to have the best acoustics. For small rooms, the best bet is to have a significant amount of absorption to eliminate as much of the room as possible. Also, in my case, the single room will serve as both recording space and a control room, which ideally require different acoustics. For mixing, one wants a fairly dead room, while the recording room can be more lively. I will strive for a compromise and see what I can do.

Main Issues

Room Modes

Every room has "modes", resonant frequencies that are a function of the length between the various hard surfaces. Modes are relatively easy to calculate. For a room with 2 parallel walls X feet apart, there is a fundamental mode at 1128/X, the frequency where the walls are one wavelength apart. There are also modes at all multiples (harmonics) of this frequency. Ideally modes are spaced somewhat evenly and relatively close together, so that no one frequency stands out. Problems arise in small rooms where there are sparse modes through the lower frequencies, and also in rooms whose shape produces the same mode from multiple dimensions. In the worst case, a square room, 10 X 10 X 10, has the same modes in all three dimensions, which will reinforce those frequencies.

One way to reduce the impact of modes is to introduced broadband absorption, to absorb the resonant frequencies. One can also build traps tuned to specific frequencies if needed.

Reverb time

The reverberation characteristics of rooms are measured as the time it takes the reverberation of an impulse, like a clap, to be reduced by 60 DB. This time is called the RT60 of the room. This time can be calculated based on the room size, shape, and materials on the walls, and it can also be measured. The RT60 is frequency dependent and may vary at different frequencies. I will be using the ETF software to measure the RT60 of my room. Fairly dry studios have an RT60 of 300 milliseconds or less. Acoustic music is usually aimed at 600 milliseconds. For my purposes, somewhere in between this range seems appropriate.

Reflections

Even with a short reverb time, strong reflections can make the room difficult to mix in. A reflection that causes a short delayed version of a sound to be mixed with the direct sound creates "comb filtering", which is the effect exploited by phase shifter and chorus guitar stomp boxes, and that can certainly impact the way music sounds. For the mixing area, I need a "reflection free zone" where I hear the monitors, not immediate reflections off walls and other surfaces. Parallel surfaces may also cause reflections that bounce between walls and ceiling and floor, causing problems, so I may want to do somethign to help break up the parallel walls.

What I can do about these

There are three basic types of surfaces I can work with to address both room modes, reverberation time, reflection, etc.

Reflective

Hard surfaces that reflect sound. This is what the room mostly has to start with.

Absorptive

Ssurfaces that absorb sound, like acoustic foam. It's important to absorb sound at all frequencies. Simple acoustic foam, or carpets may absorb highs but not the lows, leaving the room sounding bass heavy and muffled. To absorb lower frequencies, one can use "bass traps" or various structures designed to resonate and absorb sound at specific frequencies.

Diffusive

Ssurfaces that diffuse sound, essentially bouncing it around. This is similar to reflection, but scatters the sound in many directions rather than bouncing in a single direction, mirror-like, from a reflective surface. Diffusion is claimed to make a room sound bigger, and more alive, which is intriguing for acoustic music. However, there are seems to be issues with using diffusion in small rooms. Commercial diffuser products are expensive, but the information for building your own seems to be readily available (The patents from RPG - a company that makes diffusors - are fascinating to read, and tell you exactly how their products are made if you want to go that much work yourself), so this may be an interesting area in which to experiment.