Isolating Sources of Sound by Marc Schonbrun

Sound travels in waves, and it's always loudest directly in front of the sound source—the amplifier, the guitar's sound hole, the mouth of a singer, and so on. Once sound is released from its source, it can reflect and bounce all over a room. It's very hard to control where the sound goes.

Being able to separate sound is very important in recording. That's why isolation booths are a staple of recording studios. Being able to isolate sound is even more critical to the home studio owner because you don't have the luxury of using soundproofed rooms and isolated sources. So what can you do?

Banish It

Let's set up a scenario: You are recording a guitarist, and the amplifier is right next to the recording device. Unfortunately, because your room is small, you don't have much of a choice about placement. The guitar player, like most guitar players, loves to play his amplifier loud. You hook up a microphone and turn on your headphones, but all you hear is the roaring guitar amplifier 3 feet from you. How are you going to listen for microphone placement, clipping, or anything else for that matter? You need to get the offending sound (or player, whichever comes first) isolated so you can do your work.

If you're just starting out or have never recorded before, your first recordings might depress you a bit; you might not sound as good as you think! Little problems in pitch and rhythm will be very clear when you listen to your recorded music. Recording is, in a word, honest. Many people find it a great tool for learning their strengths and weaknesses.

The easiest way to isolate the sound is to put the amplifier in another room and close the door. The guitarist can monitor his sound through headphones along with you. This way you'll be able to hear what the recorder is hearing and not what the amplifier is forcing you to hear. Closets work well for this because they are small and clothes will also absorb some of the sound. The bathroom can isolate sources pretty well, too! And it's also a great place to record sources, especially acoustic guitars, acoustic instruments, and vocals. Since most bathrooms are tiled, the sound is very reflective and live, which can be really good for adding some ambience and reverb to your recordings. You'd be amazed at how many home studios rely on the acoustics of a bathroom for recording sources.

Using Baffles

A baffle is an object that blocks sound. It's also referred to as a gobo. If you don't have the option of isolating sound to another room, a baffle might do the trick.

Figure 8-5: Drum set baffle

Baffles are often used onstage around drum sets (see Figure 8-5), and are typically made of Plexiglas. These help to keep the drum sound from traveling out on the stage and getting picked up by other microphones. If you plan on recording a live band performance and you wish to retain any hope of mixing signals separately, you'll need baffles because sound has a nasty habit of flying everywhere if you don't control it. The drums will bleed into the guitar microphone and so on, making it hard to separate sounds and mix independently. Putting baffles between instruments can do the trick.

Soundproofing

You can do two main things to defeat sound in its tracks:

• Create dead air. Dead air traps sound and doesn't let it escape. You can trap air with a mattress, cushy furniture, or suspended (drop) ceilings.

• Add mass and density. A massive or dense object stops sound. For example, you can scream as loud as you want at a concrete wall, but you won't be heard on the other side. Because sound is produced by vibrating objects that push the air around them to create sound waves, a substance with little flex (like concrete) won't vibrate well. Less vibration equals less sound.

The best way to soundproof a home studio is to build a room within a room. After the normal drywall is hung, add sound batting, which is an absorbing material. Then hang another layer of drywall a few inches out from the original wall or ceiling. This creates a space between the walls to trap the sound, and it also adds to the mass and density of the wall. This is a common practice in professional studios, too. There are many books and resources available on soundproofing, so check the web, your local music store, and the public library near you.

A mattress makes a great baffle to use at home. Positioned a few feet in front of an amplifier or a drum set, the mattress will absorb and block some of the sounds from overpowering you. It's not a perfect solution since sound reflects to other places, but it can really help you out if you're in a pinch.

You can also isolate amplifiers by building an isolation box for them. By sealing each amplifier in a box, you create a mini–isolation room and prevent sound from escaping. You'll also need to insulate the inside of the box so the sound gets trapped there. Make sure the box is big enough to accommodate the microphone, and cut a small hole in the box to get the microphone cable out. Once you close up the box, you should be able to crank the amplifier and have little sound leakage. You'll never eliminate all extra sounds this way, but you can reduce the sound by almost 90 percent.