PRACTICAL STUDIO SOUNDPROOFING
PART 3: WALLS, FLOORS & CEILINGS. If you're serious about cutting noise
from your studio, you'll have to explore the mysteries of studding and neoprene
rubber.
When you've dealt with sound leakage from your studio via doors and windows
(see last month's instalment), usually the weakest areas when it comes to
soundproofing, it's time to look at walls, floors and ceilings. As with most
improvements I'm suggesting in this series, you can probably do the work
yourself if you want to keep the cost down.
PARTITION WALLS
The first area I'd like to cover is the studding partition wall, because if
you need to divide a large room into two -- for example, to create a separate
playing area and control room -- the only real alternative to permanent masonry
is plasterboard and studding. Lightweight studding walls don't have the
necessary mass to act as effective sound isolators, especially at low
frequencies, so we need to fall back on the two mainstays of soundproofing -- a
double barrier and as much mass as possible. If you have the space, two separate
studding walls are best, but if you don't want to lose too much room, a simple
4-inch-thick frame with several layers of plasterboard on each side can be quite
effective. However, you have to be careful how you fix this in place, as sound
energy travels quite happily within solids. You need to find some way of
isolating the frame from the rest of the structure, so that vibrations don't
travel to or from the floor, the walls or the ceiling. This isolation can never
be perfect, as the frame needs something to rest on, but providing you use
something resilient rather than solid, the improvement will be worthwhile.
Perhaps the best option is to use quarter-inch neoprene rubber sheet between
the frame and the floor, and also where the wall touches other walls and the
ceiling. Alternatively, use thick rubber car mats, or something similar, cut
into strips. (Try the
Yellow Pages for rubber, foam and plastics
suppliers if you don't know where to find Neoprene.) Some energy leakage is
inevitable via the fixing screws, but this probably won't be too serious in the
case of a studding wall.
Once the frame has been constructed, it must be panelled on each side with at
least two layers of plasterboard -- use the thicker 12mm grade if you can get
it, to keep the mass as high as possible. Ensure that the boards are staggered
so the seams don't coincide, and use temporary spacers, made from hardboard, to
ensure that the plasterboard stops just short of touching the existing walls,
floor or ceiling. Putting a layer of lightweight fibreboard between the two
layers of plasterboard can improve the damping of the wall without adding much
to the mass. Having the surface skimmed with plaster on completion will also
help, but try to keep that small gap around the edges. When the plaster is dry,
you can seal the gap with frame sealer using a mastic gun. Figure 1 shows how a
studding wall can be constructed.
Though it's simple to build, this type of wall suffers a little because the
frame itself can conduct vibrational energy from one surface to the other. To
improve on this, you could nail the plasterboard to the frame via rubber or felt
spacers, but probably the best approach is to build a double-frame structure. as
shown in Figure 2. Here the timbers are staggered to fit between each other, so
that the wall isn't much thicker than before. In either case, stuffing the void
between the two sides of the wall with Rockwool loft insulation will help absorb
any energy trying to pass through the void. The diagrams only show the timber
fitted in one direction, but in practice, studding walls comprise both vertical
studs and horizontal noggins.
IMPROVING AN EXISTING WALL
Of course, you may have an existing wall which doesn't provide enough
isolation, either because it's too thin, or because it's made from a lightweight
building material such as breeze block. Such walls can be lined with studding
and plasterboard, using similar constructional techniques to the free-standing
studding wall just described, except that you only need to cover one side of the
frame. Ideally, you should leave a small gap between the frame and the existing
wall, and, again, this is best achieved with the use of neoprene spacers. The
cavity can be filled with Rockwool before the plasterboard skin is nailed into
place.
Two or more layers of plasterboard are required to build up a worthwhile
mass, and a fibreboard middle layer may also help. Layering different materials
creates an acoustic mismatch, reducing transmitted vibrational energy and
damping out resonances. Figure 3 shows an existing wall uprated by the addition
of a studding/plasterboard layer. In all multi-layer walls, where two or more
layers of board are being used, it helps to seal the gaps between boards using a
flexible mastic or frame sealer before fixing the next layer. It also helps to
use dabs of plasterboard adhesive between adjacent layers of plasterboard, to
prevent the panels resonating independently, and if you can afford the space to
add even more layers of plasterboard, that's all to the good, providing your
floor can take the weight.
Unless you use many layers of plasterboard to create a very heavy wall, the
attenuation offered by this type of wall at low frequencies will probably be
less than that offered by a solid brick or concrete wall, but the improvement
should still be significant.
If you do need to build an internal wall, look at the ratio of the height,
width and length of your newly created rooms to see if you might be inviting
acoustic problems. As a rule, having equal dimensions for width, height and
depth is the worst possible case, as you'll end up with strong room resonances
at specific frequencies, and you should also avoid one dimension being an exact
multiple of either of the other two, for the same reason. Keep the ratios as
random as possible, and if you can slope one wall slightly to avoid having
parallel surfaces in the room, this will help minimise flutter echo. However,
don't worry if you can't avoid parallel walls, as the acoustic treatment needed
to kill flutter echoes is fairly simple.
FLOORS
If you have a concrete floor, you're probably starting from a reasonably good
position, but if the studio is in a bedroom with a wooden floor, you're going to
have problems. Not only is a typical domestic floor a relatively poor sound
isolator, most of the noisy gear, not to mention tapping feet, will be in
contact with the floor, which only makes things worse. Because of this latter
consideration, structurally-borne sound needs to be tackled, and the cheapest
first step is to fit heavy felt underlay beneath the studio carpet.
Professional floating floors can be massive and complex affairs,
but for the smaller studio you can build your own quite simply. A
floating floor is just a false floor mounted on acoustic isolators
above your existing floor, with resilient material around the edge
so that it doesn't come into direct contact with the walls. A
commercial floating floor may be cast from reinforced concrete,
several inches thick, and may be supported over a void several feet
deep, the weight being borne by springs or machine-rubber mountings,
but clearly this is impractical for most bedrooms!
There are less massive floor designs based on studding and
chipboard, or you can even buy a specially made floating floor
material comprising chipboard with Rockwool bonded to the underside.
This type of structure won't be too heavy for a typical domestic
floor to support, and though it won't work as well as six inches of
concrete on springs, it will make a very noticeable difference. One
commercial material, known as Lamella, is flooring-grade chipboard
backed with a tightly packed Rockwool material where all the fibres
are perpendicular to the board, rather like the bristles on a
scrubbing brush. Fitting the floor would involve fixing a felt strip
around the room, somewhat like a felt skirting board, and then
laying the Lamella boards atop the existing floor. Once the floor is
down, a second layer of flooring chipboard is glued and screwed to
the top, with the joints staggered. This adds strength and rigidity
to the floor, as well as preventing the individual panels from
drifting apart. Figure 4 shows a Lamella floating floor in
place.
This type of flooring may also be used as a base on which to
build a small studding/plasterboard room-within-a-room type of
studio, as long as the weight of the inner room isn't so great as to
cause the floor to bow. I'd be inclined to consider adding a third
layer of chipboard to the floor if you're thinking of going for the
full room-within-a-room treatment.
An alternative to using Lamella is building a wooden 2x2-inch or
2x4-inch frame and covering it with two layers of flooring
chipboard. This may be separated from the original floor by blocks
of Neoprene, though the most usual approach is simply to cover the
existing floor with Rockwool loft insulation, then lay the studding
raft on top of that. Observe the rules of isolation by not allowing
the floor to touch the existing walls at any point, and fill any
gaps with mastic to ensure the floor is airtight. Figure 5 shows a
studding
floor. |
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Once you've done that, try to get noisy gear off the floor by using speaker
stands for your monitors (placing the speakers on blobs of Blu Tack on top of
the stands), and try putting things like guitar amps on blocks of thick foam
rubber. Drum kits are more problematic, and it's unrealistic to expect a DIY
approach to provide anything like complete isolation. The most effective way to
reduce drum kit noise is to make a shallow plinth or raft, on which to set up
the drum kit, and isolate this from the floor by standing it on thick foam
rubber. If this doesn't provide isolation, the next step is to consider a
complete floating floor (see box for details).
CEILINGS
Ceilings have all the problems associated with floors, but you don't have the
benefit of gravity to help you keep your sound isolation treatments in place.
Acoustic foam tiles stuck to the ceiling might look good, but in practice
they'll keep out very little sound. A professional studio designer would
probably specify a false ceiling, probably quite a heavy one, but in the home
studio you have to be a little more pragmatic. As mentioned in last month's
instalment, your first step should be to fit underfelt to the room above your
studio. Even if this room belongs to someone else, offer to pay to have it
fitted.
If you're serious about going further, you need to know whether the floor
above consists of floorboards or chipboard. Chipboard floors are reasonably
airtight, but floorboards may well have gaps, in which case you'll need to
remove the ceiling plaster or plasterboard to expose the joists (don't do this
if it isn't your property!). This will give you access to the floorboards of the
room above, whereupon you can set about filling all the gaps with mastic. A more
thorough approach is to fit barrier mat between the joists, as shown in Figure
6. Barrier mat is a material that has many uses in studio construction, but
you're unlikely to find it anywhere other than at a studio materials suppliers
-- they don't have it at the usual DIY superstores! Barrier mat is a
mineral-loaded plastic material that looks rather like a black, flexible lino
and is very heavy. It may be fixed in place using a powered staple gun, but
you'll need somebody to help you take the weight until you've got enough staples
in to hold the material up.
Once the barrier mat is in place, the gaps between the joists can be stuffed
with loft insulation-grade Rockwool and the underside of the joists covered with
at least two layers of 12mm plasterboard. Get a plasterer to skim the
plasterboard for you and you have a smooth new ceiling, as well as reduced sound
leakage.
SUSPENDED CEILINGS
If you have the necessary room height, fitting a false ceiling can help with
sound insulation, but if you don't know exactly what you're doing this is a job
for a professional builder, as the size of the required joists depends on the
length they're required to span. This approach is shown in Figure 7. You still
have to strip the old ceiling of plasterboard and treat it, as per the previous
example, before you start. Notice that the joists for the new ceiling are fixed
in between the existing ceiling joists to minimise height loss, though if you
have plenty of headroom you can simply leave the original ceiling untouched and
build the new one beneath it. The void between the original ceiling and the
suspended ceiling should again be stuffed with Rockwool, otherwise it may
resonate.
The suspended ceiling is built from joists and plasterboard, in much the same
way as a studding partition wall, but here it rests on wooden wall plates fixed
to the original walls. Obviously, the original walls must be of solid
construction. The heavier the false ceiling, the better the isolation, but you
can introduce a layer of lightweight insulation board between the plasterboard
layers without incurring much of a weight penalty. Whether or not you isolate
the edges of the ceiling from the existing wall is up to you, but as there is no
sound-producing equipment in direct contact with the ceiling, the difference
will not be nearly so significant as it is with a floor. For the best isolation,
you need to build a complete room within a room, and that will be discussed next
month.
WARNING! Commercial studios may have up to four inches of
plasterboard and chipboard screwed to the ceiling, but don't go to extremes
without proper architectural advice.
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