Sound control, part II

This is the second part of designing your room. In the previous article we discussed how to build your room. Once you’ve finished the basic construction of the room, then you need to turn your attention to controlling the sound in your room.
Each kind of room has different needs. If you are designing a vocal booth, then you want to cover as much of the room with acoustically absorptive material. If you are creating a reverb chamber, then what you want to is exactly the opposite and have nothing but reflective, painted, non-porous surfaces. However, chances are you have a home or small studio where there is one major room that doubles as the tracking room as well as the mixing room. This article is intended to address just that kind of working space.
What determines a good mixing room? A good mixing room should closely approximate the listening environment of the end user and have a very flat response. Every room has reflections, or echo. When multiple sound waves pile up in the same place, they are called standing waves, or nodes. Nodes create an unbalanced frequency response in the room, and will affect how you mix. Why? Because if the room is bass heavy, you’ll turn the bass frequencies down. If the room is really reflective on the high frequencies, then you’ll turn those down. By taming the reflections in the room you’ll get a balanced mix.
How do you determine the right sound control materials for your room? As always, turn initially to common building materials. Rugs and carpets are a good call, as they will cover the reflective surface of the floor. Don’t forget to allow yourself a small area of smooth wood flooring so your very comfortable mixing/office chair with wheels can scoot around easily. Next, turn to the ceiling. Use of acoustic drop ceiling will prevent most reflections from the ceiling, and are economical. My favorite company, Auralex, manufactures drop-in sections of ‘diffusors’ for drop ceilings, which scatter the sound waves, providing a realistic soundscape.
Your biggest concern will be the walls. Stay away from painted surfaces like painted drywall (which is hard to do nowadays) or painted concrete. These are highly reflective. My favorite construction material is unfinished tongue-and-groove wood. I always feel that wood makes a room look and sound ‘warm.’ Once you’ve build in the walls, use lots of wall coverings such as drapes and curtains. The general rule of thumb is to cover 60% of the room with sound control products (foam). There are plenty of cosmetic foam products available today, so you can truly personalize the look of your room with choices of color and pattern. Never, ever use eggshell foam. While easy to come by and cheap, it’s got two things working against it: it’s a closed cell type, which means that sound waves cannot penetrate and get absorbed, and typically, it doesn’t meet with building and fire codes, which means it will burn up. Please, don’t ever use it to sound proof your room.
Lastly, you need to address the corners. Low frequencies tend to build up in the corners, a phenomenon called corner loading, and there are products that are designed to provide control there, too. Auralex makes a product called the LNRD, which will fit right in the corner and take the ‘boomy-ness’ out of the room.
Lastly, it’s important to use your ears! Take a really great recording (I like to use ‘The Dark Side of the Moon’) and listen to the effect of the sound of the room in the recording: some things will stand out, some things will drop back in the mix. Look around and figure out what’s causing these artifacts and then take the necessary steps to change them.