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Studio Design & Construction
This is one of the
most important links in the recording/playback chain, a professional design
approach for your Control Room, Studio, Vocal/Iso Booth. Now if you want to know
why and how all this works in a technical explanation then I suggest you follow
the reference links at the bottom of this article, and plan on spending quite
sometime on learning this from a technical view point.
In this article we are going to touch on briefly home studio design and
construction, it's up to you on how much you want to invest in this.
Now let me start out with telling you that I myself am still involved in the
learning process. What I have learned has changed my view point regarding all of
the stuff I use to think actually worked, that's why I'll leave the technical
rocket science stuff to the experts, and maybe someday it will all click and
make sense to me as well.
First lets look at some terminology regarding acoustical attenuation:
Acoustical
Attenuation ~ What is normally considered "Soundproofing" is actually the
attenuation of sound.
In electronics and audio, attenuation is the
decrease in amplitude of an electrical signal. It is the opposite of
amplification. For example a volume control on an audio system may be referred
to as an attenuator. With that same context in mind a wall, partition or barrier
is an attenuator as well, reducing the volume or amplitude from an electronic or
natural occurring sound source.
STC ~
Sound Transmission Class,
The measurement of the amount of sound that is
transmitted through a wall or barrier, the decrease is the attenuation. STC is a
widely used integer-number rating of how well a building partition attenuates
airborne sound. It is used to rate interior walls, ceilings/floors, doors,
windows and exterior wall configurations...
(more)
| STC |
What can be heard |
| 25 |
Normal speech can be understood quite
easily and distinctly through wall |
| 30 |
Loud speech can be understood fairly
well, normal speech heard but not understood |
| 35 |
Loud speech audible but not
intelligible |
| 40 |
Onset of "privacy" |
| 42 |
Loud speech audible as a murmur |
| 45 |
Loud speech not audible; 90% of
statistical population not annoyed |
| 50 |
Very loud sounds such as musical
instruments or a stereo can be faintly heard; 99% of population not
annoyed. |
| 60+ |
Superior soundproofing; most sounds
inaudible |
| STC |
Partition type |
| 33 |
Single layer of 1/2" drywall on each
side, wood studs, no insulation (typical interior wall) |
| 45 |
Double layer of 1/2" drywall on each
side, wood studs, batt insulation in wall |
| 46 |
Single layer of 1/2" drywall, glued to
6" lightweight concrete block wall, painted both sides |
| 54 |
Single layer of 1/2" drywall, glued to
8" dense concrete block wall, painted both sides |
| 55 |
Double layer of 1/2" drywall on each
side, on staggered wood stud wall, batt insulation in wall |
| 59 |
Double layer of 1/2" drywall on each
side, on wood stud wall, resilient channels on one side, batt insulation |
| 63 |
Double layer of 1/2" drywall on each
side, on double wood/metal stud walls (spaced 1" apart), double batt
insulation |
| 72 |
8" concrete block wall, painted, with
1/2" drywall on independent steel stud walls, each side, insulation in
cavities |
TL ~ Transmission Loss, When
sound hits a wall or partition there is a certain proportion of the sound that
is reflected back into the room, some of the sound is lost in the absorption of
the composition of the wall, the rest of the sound that makes it through the
wall is called the transmission loss. Good sound isolation or attenuation
reduces this transmission loss effectively.
Wall Components:
Layer ~ A single course of
wallboard material be it Sheetrock, Homosote, Plywood, OSB, MDF, Particle board,
etc... The more layers the greater the STC value.
Leaf ~ All the layers on one
side of a wall with no airspace between them acting as 1 layer.
A poured concrete wall is considered one leaf while a concrete block wall is two
because of the air gap.
The floor above a basement ceiling is one leaf and a double paned window, glass door or sliding door
is two leaves. A solid core door is one leaf while a hollow core door is two
leaves.
Spring ~ The Air Space between two leaves which in fact act as a mechanical
spring of sorts. The bigger the spring (air gap) the greater the STC value.
Mass ~ The density of
materials in the make-up of a wall. Different materials composing a layer will
have a different "coincidence frequency"
(individual resonance). This results in different weakness for each material
which lets sound (frequencies) through or strengths by different frequency
absorption.
All this is the essential make-up
of constructing an acoustical barrier or wall. Remember that if you don't have
the money to construct a near perfect audio/recording environment (there is
never a perfect room, close is best as can be done) then anything that can
be done should be done. You can establish a plan to start with a basic room then
as time goes on add more to it, eventually you could have that near perfect
room.
More Room Components:
Absorber ~ A panel or wall
made up of 2" - 4" or more of sound absorbing material such as
Rockwool or Owens Corning 703 insulation with a cloth material
barrier on the face. This is for absorbing some mid range as
well as high end frequencies. The greater the distance from the
wall (or deeper) the panel is, more mid to low end frequencies
will be absorbed. The closer to to wall the less making the
higher frequency absorption greater. This panel can be
rectangular and flush to a wall or made to be at an angle.
Bass Trapp ~ Much like an
absorber placed across the corners of a room from the ceiling to
the floor at a specified angle with slats made up of MDF or
plywood wrapped in R13 insulation with the paper glued to the
board hanging from the inside of the trapp's frame from ceiling
to floor. These absorb low end frequencies as the energy of the
bass waves move the boards and that kinetic energy turns to heat
as is absorbed by the insulation wrapped around the boards. Bass
trapps can be non-ported or ported, such as in the use of soffit
mounted monitor speakers. A non-ported trapp will have an
absorbent front with a cloth face, this will absorb high end
frequencies while letting the low end through to the trapp,
these are mainly used in the back end corners of a control room
or in the corners of a studio. A ported Bass Trapp will have a
semi-reflective surface on the front such as made with MDF
covered with a thin layer of insulation and a cloth face, with a
hole cut into the MDF at the floor and ceiling to let the trapp
breath, or can have a Slot Resonator on it's front. This will
reintroduce or reflect some of the high end frequencies back
into the room, more so the slot resonator.
Cloud ~ Just what it
implies, a cloud is frame with sound absorbing material covered
in a cloth material suspended at an slight angle over a mix desk
or any other application like a drum set etc... It absorbs high
end frequencies and help keep them from being reflected back to
the mix position or over head mics in the case of a drum set.
Some ceilings are made to be absorbent with a 6 - 12 degree
angle from a vertical line from floor to ceiling.
Slot or Slat Resonator ~
Also called a Hemholtz Resonator and much the same as an
absorber with slats of wood on the front to help reflect high
frequencies back into the room. They can be rectangular and
flush to a wall or made to be at an angle, it all depends on the
shape of the room. The slats can be made up of various widths of
wood, MDF, etc... and the slots can be spaced all to tune the
resonator to the room size. There is a calculator for this it is
called the Hemholtz calculator.
(download) excel spread sheet.
Acoustical Myths
You most likely heard these as
well. All of these applications will deaden a room (suck all the
high end frequencies out of a room) leaving nothing but low and
mid range mud in the room and making it necessary to boost the
high end in the mix causing unnatural distortion and digital
artifacts in your recording.
They are: Egg cartons, blankets, foam bed cushions,
acoustical foam products, entire floor carpeting, carpets on the
wall...The list goes on and on.
All these things absorb high
frequencies as said above, and leave you with a muddy room to record in. When
designing a room be it a Control Room, Iso/Vocal Booth or Live Room/Studio you
can't just start adding sound absorption to all or any of the surfaces. Every
room has its' own resonant frequency, matter of fact every dimension of a room
(Height, Width, Length) has its' own resonant frequency. Sound travels at 1130ft
per second and any given frequency has a wave length, the lower the frequency
the longer the wave length the higher the shorter. So considering your rooms'
dimensions you can calculate the problem wave lengths (frequencies) or standing
waves.
Figuring out the best room dimensions
The best place to start for most
home recording studios is usually the ceiling height. This is usually a
fixed dimension, using this dimension you can find your length and width using
the so called "golden ratios" from a study done by the BBC regarding recording
room specifications to help control room frequencies. The worst scenario is a
cube shaped room.
|
|
Height |
Width |
Length |
|
Ratio |
1 |
1.14 |
1.39 |
|
|
7.5 |
8.55 |
10.425 |
|
|
Height |
Width |
Length |
|
Ratio |
1 |
1.28 |
1.54 |
|
|
7.5 |
9.6 |
11.55 |
|
|
Height |
Width |
Length |
|
Ratio |
1 |
1.6 |
2.33 |
|
|
7.5 |
12 |
17.475 |
The last dimensions will give you a
good size control room with walls using the m-a-m (mass-air-mass) principle with
a two leaf system. For a two leaf system there are four common construction
methods.
The use of double wall construction with layers on
one side of each wall and a 1" gap between them like in the above image gives
the best over all isolation. This will give you 8" of air between each wall
(from leaf to leaf).
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RC Resilient Channel used
on one leaf in a single wall two leaf system
The RC keeps the sheetrock away from the framing and acts as a spring.
The sheet rock is screwed to the RC and not into the studs so it wont
short out
the stud and lower the STC rating. STC rating for this system is 40 with
no insulation and 47 with insulation. |
 |
The staggered stud method
is made up of 2x4s staggered on 2x6s. This creates a wider air gap while
giving the two leaves good isolation by not using the same studs. |
The forth method would be a single wall 1" from
a poured concrete wall with sheetrock on the room side and insulated, the
concrete wall is the other leaf making this a two leaf system.
Getting to the Room
Using the dimensions from above
we can plan to build our room. Another are to cover is trying to avoid having
parallel walls, we can build the side walls at a 6-12 degree angle or build the
room and add the sound treatment at angles to help. Also a Control Room should
be symmetrical in design to help with the stereo image.
More to come
Reference Links:
Recording Studio Design Forum -
http://www.johnlsayers.com/phpBB2/index.php
Reference Area -
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=2125
School of Audio Engineering Reference Site -
http://www.saecollege.de/reference_material/
Harman International White Papers - http://www.harman.com/about_harman/technology_leadership.aspx
Room Mode Calculator -
http://www.harman.com/xls/Room Mode Calculator.xls
Free tools & apps to help with studio
acoustics -
http://www.realtraps.com/info.htm
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