When building a home recording studio or mixing environment, 3 main areas must be considered:
- Sound Insulation
- Working Environment
Sound Insulation is the prevention of sound leakage: both "outside" sound not coming in and "inside" sound not seeping out.
It helps to think of sound as Light or Heat. Anywhere in our building where Light or Heat can escape or enter, sound can also escape or enter. Therefore, the greatest areas of sound leakage will be doors and windows. The second area to look at is sound transmission through walls.
There are 4 key points to follow to reduce sound leakage:
- Increase mass
- Make airtight
- Add absorption to cavities
- Break the vibration path
It is probably wise to remember, at this point, that no matter what you do you will probably always have to compromise in some way or another (unless you have access to unlimited amounts of money, of course!).
Acoustics is the study of how sound travels and behaves within a confined space, such as a room. Acoutics tell us that different sized and shaped rooms sound different, and that the materials that the surfaces are covered with (surfaces being walls, ceiling and floor) also have a big impact on the sound of the room, specifically it's frequency response. We must therefore understand some basic acoustic principles in order for us to build a room that will sound good, or at least meet our expectations and specifications. Indeed, depending on personal taste and on the purpose of the room (see further), we might want our room to be more or less live or dead, as well as whether the room should have a flat frequency response or not. In other words, we need to shape and treat the room to control how sound will react within this enclosed environment. See also acoustic treatment for home studio.
Different needs for different rooms.
The acoustics of a given room need to be designed to meet the purpose of the room:
- Control Room: The acoustics need to be very controlled and predictable so that the engineer / producer & the musicians can trust what they are hearing from the monitors.
- Recording room ( also known as "live" room:or "Studio"): The acoustics may be designed to "enhance" the sound of the recording. You-- may- -alz-o want to consider variable acoustics for this space, .for example very live for drums and then fairly tight for vocals. This can be achieved with thick drapes hung on a belt along some of the walls which can be pulled out when needed, rugs and carpets which can also be rolled out when needed, or the more elaborate (and expensive!) "moving ceiling panels".
- Church or Theatre: The sound needs to project forward into the room.
Special considerations for Control Rooms.
A control room needs to have very careful!y balanced acoustics.
- Frequency response: The frequency response of a control room is critical. If the room is too bassy, you will tend to mix in more high frequencies to compensate for the sound of your control room. The mix will end up being too bright and thin when played in the outside world. The same thing is true of overly bright control rooms where mix will become muddy and boomy. As the saying goes: If you can't take the room out of the mix, you can't take the mix out of the room!
- Liveliness: Same concept as above: when mixing in an overly live or dead control room, we will find ourselves adjusting our mix to compensate for deficiencies in the room rather than the recording. So the reflection= must be well controlled and diffused (see latety. Absorption is not necessarily the answer. If all the walls are covered with foam (whose main purpose is to absorb sound energy), the room will sound boomy and we're back to square one where our mixes will have too much high frequencies and little bass out in the real world. This is because foam is mainly effective at higher frequencies; lower frequencies have larger wavelengths and can travel through the foam, bounce off the wall back through the foam and still come out in the room. The other extreme would be a room with too much bass absorption (see later) causing mixes to sound muddy outside of the studio. Generally, a control room should have only a little less reverb time than the average living room. Dij not over do it: a completely dead room is not the real world and makes it very difficult to get a good mix!
- RFZ: In the mix position ("sweet spot") you will wan.: to setup what is known as a Reflection Free Zon'e: (RFZ). In the RFZ you will want to eliminate any eariy' reflections of sound. By reducing the early reflections you increase what is known as the Initial Time Delay (ITD) gap. This Initial Time Delay gap is the time between the arrival of the direct sound and the first reflections in the room. The purpose of increasing the 1TD is to allow you to hear the time domain localization cues from the i'ecording room before any reflections from the mixing room come in and confuse the issue.
To fine tune the sound of a room, we must first look at the shape and relative dimensions of the room.
- Whatever style we decide on, top of the list is Symmetry: lay out the room so that the left and right sides of the room are symmetrical. This helps with your Stereo balance. This is equally true for all 3 types of rooms described above.
- Next, we must correct any problems caused by the 3 axial modes in the room: rooms with similar • sized width, length and height create waves at different frequencies which will either be in phase (and thus these frequencies will be amplified • unnaturally at certain points within the room) or out of phase (so these frequencies will now be reduced or even cancelled, in extreme cases, at • various points within the room). These problems are clearly to be avoided at all costs.
- We must also correct any problems caused by parallel walls, namely "standing waves". Standing waves are created when you have two parallel facing walls. A frequency whose wavelength is equal to the distance between the walls will fit perfectly and will bounce backwards and forwards between the walls ontop of itself, thus amplifying itself. This will also affect that particular frequency's harmonics. So you should design a room with non-parallel walls or cure an existing room by making one of the walls absorbant or by breaking up the flat surfaces.
So the 3 ideals we are aiming for are:
- 3 complimentary axial modes
- No parallel walls.
There are essentially two ways of controlling :the frequencies and reflections in a room: absorption and diffusion. Absorption removes energy whilst Diffusion spreads out the energy in space & time.
- Placement of Absorption and Diffusion: First of all, we must create our Reflection Free Zone mentioned above. A 20ms ITD gap is a good minimum target. Any surface within 11 feet of the mix position could potentially cause a first order reflection, but treating every surface within 11 feet of the mix position is not possible or necessarily desirable. Levels of reflections earlier than 15ms relative to the direct sound should be treated to reduce them to at least 10dB below the direct sound for ; frequencies between 1kHz and 8kHz. In the area of the room between the monito and the mix position, any surface that has a 21.5 fo complete path between the monitors and the m position can also cause a reflection. One way to find the areas that need to t treated will require two people and a mirror (a plast one is preferred since you may have to tape it to pole to reach some areas). To help find the placement location, have or person move the mirror along the side walls of if control room with the other person sitting at the m position. Whenever the person sitting at the m position can see either monitor in the mirror, mark th position of the mirror on the wall. Repeat this process for the ceiling and bac wall. Any of these points that are less than 11 fel from the mix position will cause early reflections an must be treated with absorbant materials.
- Live End / Dead End: It is often preferable to not have too mud absorption in your room, otherwise it will start t sound unnatural, uncomfortable and cause difficultie when doing a mix, as mentioned previously. A populE approach is therefore to have one end of the roor (usually behind the speakers) really dead whilst th opposing wall (behind the person sat at the desk) ca be live and retain natural reverb. However, this live end should be diffused i order to make the reverb less focused and les intrusive.
- Simple Bass Trap: So far we've mentioned a lot about absorbinc which generally affects higher / mid frequencies. Lai frequencies are more difficult to treat, so what can yo do if your room is too bassy? Well there is on solution: the Bass Trap. Bass Traps are best located in corners c angles of a room as this is where low frequencie naturally build up. A simple bass trap is a resonant panel (c diaphragmatic absorber) used to absorb lo\ frequencies. They work by vibrating at these 1th frequencies and turning the sound's energy into heat. The simple way to build a resonant absorbE is to mount plywood on a 2x4 frame filled wit fibreglass. Leave at least a 1/4" space between th panel and the fibreglass or else the panel won't b able to resonate properly! Approximate absorption frequency peaks for differer plywood panel thicknesses (on a 2x4 frame filled wit 3.5" fibreglass): 1/8"=150Hz, 1/4"=110Hz, 318"=87Hz.
Last but not least, we must carefully decide how our limited amount of space is going to b utilised, and vital considerations such as ventilatior air conditioning, lighting (natural daylight?) and eas access must obviously be added to the equatior Power requirements and future proofing are also very important aspects to carefully consider before launching into the build project!