STUDIO BUILDING:
SOUNDPROOFING
The subject of soundproofing is so
problematical that it will probably make you wish you had taken up a nice quiet
career like photography! The biggest problem is that one person's music is
another person's noise. Any music that leaks out of your studio into your
neighbour's house or apartment is going to be regarded, to a significant extent,
as an annoyance. Particularly so because recording involves going over the same
piece of music again and again. You will need either to come to an arrangement
with your neighbours about how much noise you will make and at what times you
will make it, or apply soundproofing treatment to your recording room. The
alternatives could be a lawsuit and possible confiscation of your
equipment!
The first thing to note about
soundproofing is that it is impossible! There is no such thing as a completely
soundproof room. It is a matter of degree. You might reduce the amount of sound
leakage by 20 decibels, or if you can afford it by perhaps as much as 45dB or
more. The more sound insulation you require, the more it is going to cost and it
can get expensive. Good soundproofing requires three things: mass, decoupling
and attention to detail. Upholstery foam and mineral wool are great for acoustic
treatment but they are virtually useless for soundproofing because they are not
very massive and they are full of holes. Sound isn't frightened of anything but
sheer mass and the holes are an open invitation for sound to travel straight
through. To provide effective sound insulation, you need heavy walls, floor and
ceiling - the heavier the better. And rather than have one extremely thick wall,
build two walls of half the mass with an air gap in between. This 'decoupling'
means that a sound wave has to pass through four surfaces rather than two, and a
small but significant advantage can be achieved. 'Attention to detail' means
that sound will find the smallest gap to get through. No matter how massive your
walls, if there is a defect anywhere the degree of sound insulation will be very
much reduced.
If you have a choice about where
you situate your studio, think about what annoyance value any sound leakage will
have. If the room next door happens to be a child's bedroom, you might find
yourself having to shut down operations at an early hour, or monitor on
headphones. If you are thinking of moving apartment or house, look for a
property where the potential studio room is as far away from your neighbours as
possible. In a semi-detached house for example, the recording room should be at
the end of the building, not against the dividing wall between the two
houses.
Once you have found the ideal
room, or rooms if you are very fortunate or well off, then it's time to start
careful planning. The first question you will ask is, "How much money should I
spend on soundproofing?". You might probably prefer the reply, "Not very much",
but that wouldn't be true. Good soundproofing is very expensive and it could
easily outstrip your entire equipment budget at a home or project studio level.
We are going to have to compromise. Near-perfect soundproofing isn't possible
unless you have a massive budget to create an equally massive structure. Let's
start by looking at the problem areas and see what we can do to improve each in
turn.
Floor
Maybe your studio is going to be
situated in a downstairs room with a solid floor extending all the way down to
mother earth. You lucky person! You would only need to do something to your
floor if you were troubled by a nearby railway line or major road. In either of
these cases, low frequency vibrations would be very well coupled to the air
inside your studio, and from there to the microphones and eventually your ears.
Dealing with a problem of this scale is a major undertaking for which you need
to call in the professionals, and your financial advisor. Most of us however
will have floorboards whether the studio is upstairs or downstairs. In a
downstairs room, the void under the floor may act as a sound transmission path
to other parts of the house, but probably not so much to the neighbours'. You
may choose to accept this, or you may wish to follow the example of those of us
with upstairs studios who are almost bound to have to insulate the floor to some
degree. Floorboards on joists have very little sound insulating capability. The
inevitable small gaps between the tongue and groove boards offer an open sound
transmission path which we need to block. Since the existing joists are only
rated for standard domestic loading, the only complete solution would be to
upgrade the structure of the building in a similar manner to a professional loft
conversion and add steel supports to bear the weight of a thick concrete floor.
Since we are going to have to compromise, then we have to accept that the
existing joists will only take a small amount of extra mass and the
soundproofing will not be total. One example of a partial solution to this
problem was a home studio owner who used the carpet left by the previous owner
of the house, together with some salvaged carpet underlay, to provide the
resilient layer of a basic floating floor. There wasn't any need to put the
underlay actually under the carpet since no-one was going to see either ever
again. On top of the underlay were laid squares of 18mm chipboard, two layers
thick, with the joins staggered so that there was no gap for sound to penetrate.
Any acoustic designer will tell you that when you go to the trouble of
decoupling structures in this way, using a resilient layer, then the worst thing
you can do is to 'bridge' the structures. This would have happened if the
chipboard was screwed down to the floorboards, so only the two layers were
screwed together. Bridging would also have occured if the chipboard butted
directly up against the walls, so a gap of about 10mm was left. All the gaps,
between the chipboard squares and between the chipboard and the walls were
filled with mastic. Mastic can be a rubbery or bituminous compound easily
obtained from do-it-yourself merchants which is used to fill in small gaps, or
in some cases it can act as a resilient support in its own right. The rubbery
mastic that you can apply with a mastic gun is good for most purposes, the
bituminous type is best kept for more heavy-duty building projects. On top of
the chipboard was placed some more carpet underlay, and finally a carpet. Laying
your own carpet isn't so easy so it might be an idea to call in a professional
at this point.
The final result in this example
was exactly as expected. The degree of insulation through the floor had gone up
from practically zero to a level which the rest of the household could benefit
from at all reasonable hours.
Walls
Upgrading the floor in the way
described brings it up to the standard of an interior wall, just about. You
might think that this isn't too wonderful, but bear in mind that most of the
leakage in an ordinary house or apartment comes through gaps around the doors,
and directly through the paper thin doors fitted in most modern properties. For
the average home project studio, you would probably only need to upgrade the
wall separating your studio from the neighbours, unless the rest of your family
really hate your music! Once again, mass and decoupling are what we need,
together with perfect attention to detail. Most professional studios use
plasterboard supported by a wooden frame in a style similar to the BBC's famous
'Camden' partition. A double plasterboard partition would divide two areas quite
nicely, but you will probably only wish to construct one layer to add to an
existing wall. To build a plasterboard partition yourself isn't as difficult as
it looks, or you can always find a jobbing handy person from the classified
pages of the local paper. Just make sure you stick around to give the
appropriate supervision.
The wooden frame is built from
timber approximately 50mm square. The uprights are called studs, and the
horizontal pieces noggins (in England). Since the structure should be decoupled
from the rest of the building it is wedged in between resilient layers, probably
of hair felt carpet. And try and resist the temptation of rigidly fastening the
new structure as much as possible. Each additional nail or screw provides a
sound transmission path that will reduce the effectiveness of your new
partition. The studs should be 600mm apart and the noggins around 1.2m in a
staggered pattern. The two layers of plasterboard should also be staggered so
that the gaps are not aligned. It is normal practice to tape joins between
sheets of plasterboard and lay a thin skim coat of plaster over the entire
exposed surface. It is good acoustic practice too to do this. You should fill
the space in between the plasterboard with mineral wool to absorb as much as
possible any sound passing through. Once again, any small gaps around the edges
should be sealed with mastic to prevent sound leaks.
Ceiling
If your studio is at the top of
the building then it probably isn't worth doing much to the ceiling. Although
the loft space or void above is a potential path for sound, by the time it gets
through to the neighbour's property it has to go through two ceilings and the
party wall and will be reasonably well attenuated. Laying one thickness of
chipboard on top of the joists in the loft is about as far as it is necessary to
go, bearing in mind that they can't take the same loading as the joists
supporting habitable rooms. If your studio is downstairs, then you have a
problem. You could insulate the floor of the room above, but in an apartment it
might not be part of your property! You will have to add insulation to your
ceiling from below, and it will probably be tough going. Choices range from
suspended plaster tiles, which are quite good for sound absorption, but will
only give around 10dB insulation at higher frequencies if you are lucky, through
to additional layers of plasterboard, keeping in mind the load bearing capacity
of the joists. If you want to be ambitious and you have the height available,
then you could fit metal joist hangers to the walls and create a separate
structure akin to a Camden partition. You will definitely need an assistant and
plenty of DIY/home improvement skill for this.
Doors
Domestic doors are so light that
they hardly act as a barrier to sound at all. And what sound doesn't go straight
through will easily seep around the edges. The easiest solution is to buy a fire
door which will be solid and have much better intrinsic insulation, and fit it
into a frame which seals all the way round. You could make a door out of two
layers of 18mm chipboard with hardwood inserts to support the hinges. Extra
battens around the inside of the door frame where the door closes, and also at
the bottom, will help give a good seal all the way round. The actual sealing
element can be neoprene rubber strip and the result should be reasonably good.
Apart from going to the professionals, the next step would be to build a small
lobby outside the studio so that a second door could be fitted, and on balance
this is probably a better recommendation to the do-it-yourselfer in preference
to trying to build and hang a really heavy door. Remember that a heavy door
needs a heavy frame, and a heavy frame needs to be very well fixed to the wall.
If you fit the door frame yourself, don't forget to seal around the edges with
mastic or this will be another potential sound leakage path.
Windows
Where studio doors are a bit of a
problem, windows are a lot easier than you might imagine. The easiest route
would be to have conventional double glazing fitted which will provide a little
extra sound insulation. For almost complete protection against noisy neighbours
(and the reverse), purpose-made secondary double or even triple glazing is
appropriate. The first thing you will need to do is get used to the idea that
you are never going to open your window again. Let's face it, there's no worse
window from a sound insulation point of view than an open window! After this,
the next step is to measure up the opening very carefully and order some glass.
Professional studios use very thick glass which is correspondingly expensive. We
are going to use 6mm glass which is thicker than ordinary domestic window glass
but not too costly. The essential points to bear in mind are these:
- Don't underestimate how
dangerous glass is. Even when it is stored leaning against a wall you could
brush against it as you walk by and gash your arm. Even one square metre of 6mm
glass will be very difficult to handle alone, so have an assistant, and both of
you must wear protective gloves and goggles.
- The glass should be set in
mastic so that it is decoupled from the frame.
- Clean the glass meticulously
in a good light before you install it. Any dirt or fingerprints you leave behind
on the outside will remain there for you and your associates to see for the life
of your studio. Put a bit of disinfectant in the water too or you might soon
find small circles of fungus growing between the panes.
- Paint or varnish the outside
of the secondary glazing frame too. You may think that it won't show, but on a
sunny day you will see its reflection in the outer window.
- Line the reveals of the window
with carpet, fixed with strong glue, to absorb sound that gets through the
panes.
- Once again, treat glass with
the utmost respect.
Ventilation
Once you have completely
soundproofed your studio, you have completely air proofed it as well! It's easy
to forget how much we depend on ventilation through the small gaps between walls
and windows and doors. Without ventilation, your studio will quickly become the
stuffiest place on earth and two people working in the same room together with
heat generating equipment will force the temperature up to unbearable levels
even in the depths of winter. Air conditioning would be nice, but at the very
least you need ventilation to bring fresh air into the room and expel stale air
out of it. A free standing fan within the room will recirculate the stale air
and give you a bit of a breeze but no overall benefit.
One idea for the upstairs room of
a house is to cut a hole in the ceiling and fit an extractor fan in the loft
above. Cut another hole close to the outside wall so that air can be drawn in
from the eaves of the house. Unfortunately, fans are generally quite noisy, so
you must take steps to reduce the noise as much as possible without restricting
the air flow. The fan is mounted in a box which stands on top of a resilient
layer, actually some packing material that came with a piece of equipment.
Decoupling the fan from the structure of the building makes a big difference to
the amount of mechanical noise that gets through. To reduce the noise coming
down the duct (which since the fan is an extractor, has to travel against the
air flow), line the box with mineral wool (sold as Rockwool in the UK). Putting
some Rockwool in the duct will reduce the noise very effectively but it also
reduces the air flow. Recommendations for ventilation are as follows:
- Use as powerful a fan as you
can find. Also, a bigger, slower running fan will be less noisy than a smaller,
faster running one.
- Use as large a diameter duct
as you can find. The lower the velocity of the air, the less noise will be
produced by turbulence.
- You can make a duct from
chipboard or MDF (Medium Density Fibreboard). If you line it with mineral wool,
even more noise will be absorbed. Make sure that all the joins are well sealed
or the fan will suck air through any gaps and not from your studio.
- Don't blow air through or past
Rockwool into your studio, unless you want to clog up your equipment and lungs
with mineral wool fibres.
- Place the exhaust vent as far
as possible from the fresh air intake.
- Bear in mind that noise will
escape from your studio through the vents so place them where the noise will do
the least harm.
These solutions will transform
a significant noise problem into something manageable but it won't eliminate
sound leakage entirely, particularly if you want to record heavy rock bands in
your studio! Bear in mind that there is no point in having fantastically good
insulation in the walls when the floor and ceiling are not up to scratch. If you
want to achieve higher levels of sound insulation, the only sensible solution is
to call in a professional acoustic designer. Do-it-yourself is fine up to a
point, but if you want to go beyond what is suggested here then you need
professional help otherwise you may spend a lot of money and not achieve the
degree of insulation you need.