acoustic room question

Every dimension of the room has associated "modes". For example, a room might have a dimension that produces modes at 60, 120, 180, and 240 Hz. Let's say the dimension is 16 feet. If a second dimension is also 16 feet, then you double the magnitude of the modes. If the ceiling is also 16 feet, you triple the magnitude of the modes. This is bad. The room will sound best if the modes are spread-out. I made a spreadsheet using room modes to help me pick the dimensions of the theater room in a house we had designed by an architect. I ended up with 10.5 foot ceiling height (flat), 19.5 foot width, and 23.5 foot depth. That room sounded different than every room in the house, even before it was finished with drywall. Next... you don't want dimensions that are all divisible by the same number... so 8x14x18 would be bad because each dimension can be divided evenly by 2. That will cause modes to stack-up also. 9x12x15 is also bad because all 3 dimensions are evenly divisible by 3. 9.5 x 11 x 17 would be better.

The other major factor is absorption and scattering of the strongest reflections. Put a mirror on the side wall. Sit in the main seat. Have someone move the mirror until you can see a speaker in the mirror. That's a reflection point. You can use a diffuser on some reflections, and an absorber for others. Absorbers work best for anything beside and in front of you. Diffusion works better for the sound behind you. Diffusers have unequal/uneven reflective surfaces. Absorbers grab sound and trap it to remove the reflections.

Next, long expanses of ceiling or wall (or floor, if it has a hard surface) are really bad for echoes. Do as much as you can to interfere with long expanses of unbroken wall, ceiling, or floor. There are decorative "beams" made for interior ceilings. Those can be wrapped with fiber-fill and then be wrapped with a loose-weave fabric to allow sound to get through the cloth and trapped in the fiber-fill. It's surprising how much better a room can sound without audible echo in the seating area.

Never use too much absorbtion or diffusion. Sound quality will actually get WORSE if you over-do either one. There should be a nice balance of absorbtion and diffusion in the room.

briannarichardson2 said:

What are the key factors to consider when designing an acoustic room for music production or sound recording purposes? How does the size and shape of the room impact the acoustics and what methods can be used to mitigate

any negative effects? How can materials such as wall insulation, ceiling tiles, and flooring impact the sound quality of a room? Is it necessary to use specialized acoustic treatment such as bass traps, diffusers, and absorbers, and how

should they be strategically placed within the room for optimal sound quality? What role does room resonance play in the sound of a recording, and how can it be adjusted to achieve a desired sound? How do room reflections and

reverberation time affect the overall sound quality, and what techniques can be used to minimize their impact? Finally, what are some common mistakes to avoid when designing an acoustic room, and how can one ensure that the final result meets the desired acoustic goals?

Click to expand...

Sounds recording is often done in what is called a Live Room, in the sense that sound is created "live" in that room. The size and materials used in such a room, and the acoustic goals, are often quite different from the room in which one listens to the recording, and mixes and masters it. The is often called a Control Room, and has different properties, and acoustic goals.

Things like "golden ratios" in terms of the room size and construction can make a difference.......and many of the best sounding rooms don't conform to any specific shape, but are well treated and well set up. If you have the money to build a room from scratch, including choosing the dimensions of the walls, floor and ceiling, and the materials used, you probably want to spend the first ten thousand dollars of your 200 thousand dollar budget on a expert like PMI engineering, in Marin County, California, or similar, so that you get it right.

But to get a sense of what it takes and what to discuss with the architect and builders, or if this is a DIY project, this book is the best source to start with:
Home Recording Studio: Build It Like the Pros 2nd Edition
by Rod Gervais

Nathan is correct in that studios have more life than control rooms, and many have variable acoustics for different styles of recording, and indeed the different acoustics provide a ‘signature sound’, eg Abbey Road.
The Salford ratios are related to Control Rooms specifically.
Rod Gervais‘ book is excellent, and on my shelf, as is the more introductory one by John H Brandt, both regular contributors on Gearspace Acoustics forum, along with a few other professional acoustic designers.
From experience, and if there’s available space, a larger room with the right dimensional ratios will reduce specialised and expensive treatments.
In my 6m x 9m x 4m room there’s only 3 devices, all on the back wall. The rest is common house insulation and 25mm sheets of Rockwool, simple enough for DIY installation.