RECORDING STUDIO ACOUSTICS DESIGNING

BY:SHIVANGI SAINI13/AR/010

RECORDING STUDIO

A recording studio is an assemblage of equipment, spaces and persons such that a performance in sound may be created and recorded onto a medium for later reproduction.

Reverberation

Reverberation is the collection of reflected sounds from the surfaces in an enclosure like an auditorium. It is a desirable property of auditoriums to the extent that it helps to overcome the inverse square law dropoff of sound intensity in the enclosure. However, if it is excessive, it makes the sounds run together with loss of articulation - the sound becomes muddy, garbled. To quantitatively characterize the reverberation, the paramater called the reverberation time is used.

Reverberant sound is the collection of all the reflected sounds

Recording Studio Acoustics

The desired acoustic properties of a recording studio are in many ways the opposite of those of an auditorium. Instead of enhanced reverberation, it is usually desirable for the recording studio to be acoustically "dead", having a very short reverberation time.

IMPORTANCE• Not only does this require the enclosure itself

to be very absorbent of sound, but soundproofing becomes very important.

• In order to prevent the passage of low frequency sounds such as traffic noise, aircraft noise, etc., the recording enclosure is often isolated from the main structure with a double wall.

• Since low frequency sounds are much more efficiently borne by solid structures than high frequencies, the suspended "room within a room" strategy minimizes the structural linking of the recording room to the foundation of the building.

• Careful sealing of the enclosure and careful design of the heating and air-conditioning system are necessary.

• Sometimes additional bass traps are employed to further reduce low-frequency background.

SOUNDPROOFING

Soundproofing of a room involves the isolation of that room from audible sound from the outside and may be taken to include the acoustic damping of the room itself. Preventing the entrance of sound from the outside is accomplished by sealing openings, making the walls absorbent of sound, and minimizing the passage of sound energy through the solid structures of the walls. Sound absorbing materials such as foam insulation in the walls help with both the sealing and absorbing of mid-range to high frequency sounds, but bass frequencies tend to be efficiently borne through solid structures. To isolate a room such as a recording studio from low frequencies, the "room within a room" approach is often taken. A double wall structure can greatly reduce bass transmission.

BASS TRAPS

The damping of unwanted sounds is an important feature of recording studios. The bass frequencies are often troublesome because they diffract through small openings and are more efficiently structure-borne into the recording area. Bass traps which make use of the nature of cavity resonance are used to advantage. If a particular bass frequency range is troublesome, a large cavity can be constructed which will offer resonant absorption in that frequency range. Some recording studios have closet-like carpeted enclosures which have a movable baffle as the opening. Positioning the baffle can tune the absorption, since the area of the opening is one of the variables which determines the resonant frequency of a cavity. A tuned cavity which is reflective can enhance the sound at the resonant frequency, as in a bass-reflex speaker, but if the cavity is covered with absorbing material, it will selectively absorb sound energy at that frequency.

SOUND PROOFING

Technical Considerations

Usually commercial considerations will dominate the choice of site. Thereafter the difficulty is achieving the desired technical specification within the available budget. Having chosen a suitable location the next set of problems appear... 

Wherever you decide to put a studio there is likely to be some form of unwanted noise like vehicles, aircraft, people taking etc.

External noise Building construction

With an existing building, it will generally be necessary to construct some form of independent structure within the existing walls, and the building's structure will need to be suitable for this, or modified accordingly,

Internal noisethe likely noise sources within the finished studio need to be evaluated and provision made to isolate them acoustically. A condenser microphone can pick up the noise from a 'soil pipe' from quite remarkable distances!

Floor loadings

With an existing building, allowance has to be made for sound treatment being laid on top of the existing floor, as well as the loading to go on top of that. 

SHAPES OF STUDIOS

Many shapes in control rooms are varying depth and types of acoustic treatments. The boundaries are rectangular.Shape may be a real advantage for performance rooms. But this is not true for control rooms. Why?

• Control rooms need to be symmetrical, Studios do not.• Control rooms need to be predictable and accurate. Studios just need to sound good.• Control Room acoustics require shorter reverb times. Longer reverb is often desired

in the “live” room.• A good control room should sound the same as you move through the room. A large

uniform “sweet spot” is desired. A good studio has varying acoustical character throughout the room providing different ambience for recording flexibility.

• Line-of-sight, shape in the studio often provides better eye contact. Control rooms are best when the view is stable at the mix position.

Often rectangles and squares are divided on the diagonal for efficiency of space. The diagonal line is a longer dimension.

CONSTRUCTION TECNIQUES

Walls

• Building a home recording studio requires good walls. • The most effective soundproofing must be designed into a house when it is first built. • A typical residential wall is made of a frame of 2x4 wood studs covered with 5/8" thick

gypsum board. 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 gypsumboard 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!

The picture shows the blue wall studs attached to one side and the green ones to the other (diagram is looking down at the top of the wall).

INSULATION

 Key idea to consider: fill the walls with cellulose insulation . The result is much more sound blocking.Showing cellulose in the walls and fiberglass in the floor.ALL the joints where studs meet the outside wall. This makes the wall airtight, and increases the sound proofing.

FLOORS

This is an effective way to decouple the floor from the structure, helping to eliminate noises traveling in the frame of a building.

WINDOWS

A Sample Design

As an example of how to apply these principles, let us look at an ordinary room in a typical house. (All right, it's my wife's studio in my house!) This room is rectangular, about 11' by 13' with an eight foot ceiling. There is a large closet at the back of the room and a window at the front looking onto a suburban street. The closet helps isolation because it provides something of a double wall between the studio and the living room.

Acoustic Design

By "acoustical design" in relation to building a home recording studio, I mean those things you do in construction that are specifically designed for acoustical applications in building a recording studio. These are not things like foam panels and acoustical treatments (that comes in the next section), but things like insulation, floor support, and drywall hanging aids. Here are the common options available to someone looking at building a home recording studio.

U-boats

The work to decouple the floor joists from the subfloor. The principle is simple - load these boots around the floor joists and set them on the existing floor. The rubber dampens any vibrations, and takes care of wandering shocks that want to get into the recording. Here is a picture showing them in use.

Drywall hanging channel (RC-8 Channel)

 an airspace between two walls is very effective in adding to the STC or sound proofing factor of a wall. RC-8 channel is an easy way to achieve this without building a second wall.

Sheetblock

This is a rubber sheet that comes on a roll. The goal is to introduce more mass to the wall in a thin, small package. This product gets glued to the wall, usually in a layer inside the wall. Sheetblock adds considerably to the STC level of the wall but is very thin. This makes it ideal for a small but effective treatment.

ACOUSTICAL TREATMENT

DIFFUSORS AND ABSORBERS

• Diffusors are used to reduce or eliminate repetitive echoes that occur in rooms having parallel walls and a flat ceiling.

• Although there are different philosophies about how much natural reverberation recording studios and listening rooms should have, all professional studio designers agree that periodic reflections caused by parallel walls are best avoided.

• Therefore, diffusion is often used in addition to absorption to tame these reflections.

• The simplest type of diffusor is one or more sheets of plywood attached to a wall at a slight angle, to prevent sound from bouncing repeatedly between the same two walls.

• Alternatively, the plywood can be bent into a curved shape, though that is more difficult to install. In truth, this is really a deflector, not a diffuser, as described in more detail below.

• However, a deflector is sufficient to avoid flutter echoes between parallel surfaces.

FIBERGLASS BASS TRAPS

A thick piece of 705 mounted across a corner is effective to fairly low frequencies

There are a number of ways to create a bass trap. The simplest and least expensive is to install a large amount of thick rigid fiberglass, spacing it well away from the wall or ceiling. As noted earlier, 705-FRK that is four inches thick and spaced 16 inches away from the wall can be quite effective to frequencies below 125 Hz. But many rooms have severe problems far below 125 Hz and losing twenty inches all around the room for thick fiberglass and a large air space is unacceptable to most studio owners and audiophiles. Fortunately, more efficient bass trap designs are available that are much smaller. However, studios on a tight budget can apply rigid fiberglass in the room corners as shown in Figure 3a and lose only the small amount of space in the corners

 Sound striking the plywood front panel causes it to vibrate. The fiberglass then damps that vibration.