Studio Acoustics

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Why Should I Care about my Studio's Acoustics?

The acoustics of your studio have a great effect on your recordings. If the room you are recording in has a lot of background noise, that will often show up on the final recording. If the walls of your room are too reflective, then your recordings may have echoes. Or if the room you're recording in doesn't have enough reflective properties, your recording could sound "dead."

Soundproofing

The most important sound in a studio takes place before an instrument is ever played. The sound of air. For a home studio, the sound of air is often not as silent as one would like. Heaters, water-pipes, traffic, and next door neighbors and alike make noises that can end up on your recordings. Here are some things you can do to minimize them.

How Sound Moves

According to Wikipedia's contributors, sound is "the vibration of matter, as perceived by the sense of hearing. We usually hear vibrations that travel through air, but sound can also travel through gases, liquids and solids. It cannot travel through a vacuum (such as exists in outer space). When the vibrations reach our ears, they are converted into nerve impulses that are sent to our brains, allowing us to perceive the sound."[1]

A sound wave is essentially energy in motion. When a bell is hit, kinetic energy transfered from the mallet to the metal of the bell makes the bell. That energy is what makes the bell vibrate. When the bell is vibrating, it acts like the mallet against the air, thus transferring the bells kinetic energy to the particles of air, making the particles vibrate. When those particles hit a microphone, the microphone vibrates. That is how sounds gets to a microphone.

Whenever kinetic energy is transfered from one medium to another, such as the mallet to the bell or the bell to the air, some of the energy is lost in the transition, in accordance with the second law of thermodynamics (see Wikipedia's Article on Entropy.)

The amount of energy lost depends on the medium. For example, air is generally a poor medium for sound compared to most solids and liquids because it is not very dense. Sound travels about four times further underwater, for instance. The less energy a sound wave has, the quieter it gets.

In order to reduce the sounds, it is necessary to put as many poor mediums between the sound and the microphone as possible.

Soundproofing a New Studio

When building a new studio, there are many effective soundproofing methods.

Walls

Walls of your studio may play the most important soundproofing role in your new studio, particularly if the studio is an addition to a house or in a noisy neighborhood.

Peter Elsea writes "A typical residential wall is made of a frame of 2x4 wood studs covered with 5/8" thick gypsum board. Properly built (no holes!) this will provide about 35 dB of isolation. Fiberglas filler, R-7 or better, will increase this by 5 to 8 dB and decrease wall resonance. Doubling the thickness of gypsum gives another 3 to 6 dB of overall isolation, but its most important effect is lowering the resonant frequency, hopefully below the audio range.

There are two common strategies for reducing coupling between the two sides of the wall. One is to make the gypsum-to-stud connection springy, either by using metal studs or by hanging the gypboard on resiliant metal bars. The most effective trick is to use separate studs for each face of the wall so there is no direct connection. This eats up a lot of space, but can give a transmission loss of over 60 dB. This is actually better performance than simple cinder block or poured concrete construction!" See his article ACOUSTIC TREATMENT FOR HOME STUDIOS for diagrams.

For soundproofing purposes, floors and ceilings should be considered walls.

Windows

Generally, windows to the outside are a bad idea in a studio, particularly if they are open.

However, most studios like to have a window between the control room and the studio space for communication purposes. There are two ways to create this window.

The most effective window in terms of viable sound proofing is a video camera. A cheap camera and monitor can allow an engineer to see inside the studio without a physical mirror. However, this method doesn't allow for easy visual communication between the engineer and the artist.

The second option is to build a window using the idea of a double wall construction. The window should be solid (not sliding) and be sealed around the edges with rubber. There should be two panes and they should be as far as possible from each other, usually also they are not exactly parrallel. The windows frame should not bridge the two studs.

Avoiding Common Building Noises

All buildings make noises that most people simply ignore. Office lighting usually buzzes, sometimes using a floor lamp with an incandescent bulb can bypass this. Air-Conditioners, heat vents, and Water-pipes are also some of the biggest contributors.

Don't run water-pipes in the walls around your studio. This should minimize the noise of toilets flushing, etc.

Air ducts can be soundproofed by using baffles (See Peter Elsea's article ACOUSTIC TREATMENT FOR HOME STUDIOS for construction tips.)

Sound Within the Studio

Once the noises from the outside are silenced, the way a room changes sounds becomes important. There are two ways a room can change a sound: Reflection and Absorption.

Reflection

Reflection happens when a sound hits a hard and flat surface. The effects of reflection include both echo and reverberation (reverb).

Echo is when the first reflection happens a long time after the original sound, often loud enough to creating echos of its own.

Reverberations are quick reflections (and reflections of reflections) that build up, sustaining the sound rather than repeating it.

Reverberation Time is the amount of time it takes a sound to drop 60dB, making it more or less in audible.

Absorption

Absorption is the opposite of Reflection, taking in the sound rather than bouncing it back into the room.

Peter Elsea writes "Every material has some absorptive qualities. This is described by its coefficient of absorption, a number between 0 and 1, with 0 being totally reflective and 1 being an open window. For instance the COE of brick is 0.04, whereas that for heavy drapes is around 0.6. The effective absorption of a surface is simply the COE times the area of the surface in square feet. These numbers can be used to compare materials and to predict the results of treatment. The absorption ability of most materials is frequency dependent, which can cause problems..."

Standing Waves

Wikipedia's article on Standing Waves says "A standing wave, also known as a stationary wave, is a wave that remains in a constant position. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions."

In sound speak, this means that one certain sound or frequency will reinforce itself, causing it to be louder and last longer than other sounds (this is the effect so commonly heard in bathrooms and showers.) Standing sound waves are caused by reflective parallel walls.

To fix standing waves, a studio must either be built without parallel walls or if a room is being retro-fitted to be a studio, diffusers can be put in place.

Diffusion

Diffusion occurs when a sound is reflected off of a round or complex surface, such as a series of pyramids.

Retrofitting an Old Room into a Studio

Pick the Space Wisely

Make sure the room you pick isn't near any loud rooms, such as an entertainment room, bathroom, kitchen, or garage. Also, keep in mind what sort of noise your studio will be making. If you will be recording loud guitars for instance, make sure not to put your studio next to a roommates office.

Fix'n a Hole

Most rooms aren't constructed with soundproofing in mind. This often means that there are holes where sound can get through.

The most common culprit is the room's door. This can be easily fixed by using the same techniques you would to weather-strip a house. See Peter Elsea's article ACOUSTIC TREATMENT FOR HOME STUDIOS an indepth explanation of the weather-stripping methods.

Citations

1. Wikipedia contributors (2006). Sound. Wikipedia, The Free Encyclopedia. Retrieved 03:05, February 12, 2006 from http://en.wikipedia.org/w/index.php?title=Sound&oldid=38846607.

2. ACOUSTIC TREATMENT FOR HOME STUDIOS by Peter Elsea

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