Soundproofing Your Home Recording Studio

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CM58.acoustics

21/2/03

12:59 pm

Page 60

Hear no
Your room can have
a huge impact on the sound
quality of your finished
tunes. Even if you’re on a
limited budget, you can
dramatically improve your
monitoring environment
using everyday materials
that you may already own...

rch
agicto
tion: M
Illustra

t’s an unfortunate fact that most project
studios are rectangular or square. But admit it,
if you had £2,000 to spare, what would you
do: consult an architect to modify your room, or
spend the money on new gear? You’d spend it on new
gear, wouldn’t you? It’s always easy to tell yourself you
can ‘get by’ with your room as it is, but somehow
there are always excuses to buy new equipment.
The fact is that acoustic treatment is vital for
professional results and in major studios, extreme
measures are taken. The rooms may have strange
geometry. The walls and ceilings may be false and
constructed out of fabric stretched over wooden
frames. Behind these, suspended from the roof, you
might find large panels covered in sound-absorbent
material. The studio doors may be oversized, filled
with sand or lead, and mounted on industrial-strength
hinges. The entire room might even be of a floating
structure to decouple it from the rest of the building.
In a small, home-based project studio room, such
measures are impractical – the space left over after
treatment would be too small to use – and expensive.
But even if you are on a tight budget, it is possible to
dramatically improve the sound quality in your room
using everyday materials that you may already have
lying around your home. So, now that you’ve cleared
out all the junk from that spare room to turn it into a
studio, we’re going to, er, tell you to put it all back
in again!

I

Go untidy your room
Perhaps the first question we should consider is why
room acoustics can turn out to be such a huge
problem. The answer is surprisingly simple: any object
can reflect sound, and such reflections interact and
can cause problems that spoil one’s ability to hear
music properly.
Solving these problems isn’t particularly
straightforward. While most materials allow low
frequencies to pass straight through them, materials
that are soft and lightweight tend to absorb high

60

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evil

frequencies, yet hard and heavy materials reflect them
back. Ultra low bass frequencies have an remarkable
ability to pass through almost anything (just ask your
next-door neighbours).
We need to use a combination of different
materials to solve these problems. Before we do that,
though, let’s take a look at the problems that
unwanted sound reflections can cause.
Firstly, if a sound is reflected in phase with itself
(ie, both the original sound wave and its reflection are
in synchronisation and are perfectly overlapping each
other), then that sound becomes reinforced, making it
considerably louder. This results in the characteristic
boominess of some rooms. This can swamp the room
with sound, making it difficult to hear clearly.
Secondly, if a room is built in a solid and
soundproof manner, bass frequencies build up at the
edges of the room, so that the mix sounds radically
different depending on where in the room you
happen to be standing.
Thirdly, if a reflection is out-of-phase (ie, the
positioning of the reflected waveform clashes with the
original), it causes a comb-filtering effect, making
some frequencies leap out more than others. This can
mask problems in your mix or exaggerate issues that
wouldn’t normally be a problem. As each ear will
receive a different reflection pattern, the stereo
imaging can also become unclear, and it can be very
hard for your brain to identify the different
instruments in the mix clearly.
If we strive to eliminate every unwanted sound
reflection, the resulting sound of the room becomes
too unnatural and artificial. It doesn’t represent the
kind of environment that the mix will typically be
played back in. The room feels ‘dead’, claustrophobic
and unpleasant to be in. Our brains analyse everyday
sound reflections to help orient us (similar to bats in
caves), and if we deny ourselves such information, we
quickly feel boxed in and extremely uncomfortable.
We need an environment where low frequencies
don’t accumulate and swamp the sound, and an

environment with a diffuse high-frequency
soundfield, creating an uncoloured sense of space in
the room we are listening in.
You can spend a lot of money treating your room
to professional standards, but frankly, this is not
money well spent unless you regularly hire out your
studio to paying clients. Most of the benefits of
effective acoustic treatment can be achieved for little

or no cost if you’re prepared to sacrifice a little room
space and be imaginative and creative in the way that
you use what is available to you.
But before starting, you need to decide whether
the approaches we’re about to run through will work
for you. Don’t start off unless you are sure that you
can get the results you need, and that any bits you
need to buy are within your budget. Work out what

How sound travels

We’re so used to seeing the familiar wavy line display – shown in picture 1, above – on computer-based
sound editing software that it’s easy to forget that this bears no resemblance to how sound actually moves
in the air.
When a sound source starts to vibrate, it compresses the air around it. As the air expands again it
compresses the air around it, and that, in turn expands. So, the wave action travels outwards like a set of
huge wobbly concentric spheres, similar to the cross-section view shown in the lower picture above.
So in reality, the actual air around the sound source doesn’t travel to where the sound is picked up. Instead,
it is merely the ripple-like action that is transferred to the receiver in a sort of ‘falling domino’ effect.

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items you can recycle from around your house (or
from the local rubbish tip), and what things you’ll have
to buy.
OK, that said, let’s look at the specifics of solving
these problems.

Reducing room resonance
If two large walls are directly facing each other, some
sound will keep bouncing back and forth until it is
dissipated as heat or cancels itself out. If the length of
the sound wave is exactly the same as the distance
between the two walls, it gets reinforced and the
room resonates in a boomy way. In fact, if the distance
between the walls is any exact multiple of the sound’s
wavelength, then some degree of resonance will
always result.

The audible effect of resonance depends on the
size of the room, but dry drum patterns will show up
the defect best. Try comparing different types of
snare and bass drum samples, listening first on
headphones, and then on speakers. The drums should
be clear-sounding in both cases. A poor, resonant
room will add unwanted colouration that isn’t there
when listening on headphones.
Room resonance happens in three dimensions:
between the two side walls, between the front and
rear walls, and between the floor and the ceiling.
Typically, the resonance between the floor and ceiling
is very much lower, due to floorboards, carpet, and
thin ceiling boards reflecting much less sound than
hard side walls tend to. We need to break up the pure,
rectangular nature of the room to solve this problem.

The solution is simple. Large items of furniture,
cupboards, wardrobes, bookcases and display cabinets
will break up the room into smaller, less resonant
spaces, and will also help absorb sound.
But be aware that cheap wardrobes and cabinets
can cause problems if their panels are not solidly
constructed (especially the large back panel). There is
a simple test: bash the panels lightly using the soft
palm of your hand. The sound they make should be
little more than a ‘slap’ or a ‘thunk’. If any of the panels
boom like a bass drum, you know you’re in for trouble.
Often, you need only to nail the troublesome panel
into place more securely to solve the problem.
You don’t want to turn your nice studio into a junk
room, but you have to compromise. Those fantastic,
minimalist rooms you see in hi-fi adverts are sheer

The problems
speaker

speaker
speaker
work bench

low profile
equipment
rack

speaker

speaker
low profile
equipment
rack

work bench

speaker
low profile
equipment
rack

work bench

chair
chair

chair

entrance door

walls will cause the room to hoot – or resonate – at
that frequency as the sound keeps bouncing between the
walls. Most rooms have three such fundamental
frequencies: one between the side walls, one between
front and back walls, and a third between the floor and
the ceiling.

entrance door

entrance door

1 Any waveform that fits exactly between parallel

2 Direct and secondary ‘live’ reflections from the walls,

ceiling, and any large, flat objects in the room
confuse the stereo imaging and make it difficult to hear
exactly what’s happening in terms of instrumentation.

3 But a completely ‘dead’ room that absorbs all the

sound lacks essential everyday audio clues that tell
the brain how big a room is, resulting in an unnatural
monitoring environment that feels small and cramped and
can even induce strange feelings of panic.

The solutions
display cabinet
speaker

display cabinet

bass trap
speaker

work bench

speaker
low profile
equipment
rack

work bench

chair

storage
cupboard

bookcase

entrance door

1 Bulky items of everyday furniture such as bookcases,

cupboards and shelves will break up a room into a
non-rectangular shape. The problem is now distributed
over so many different areas that it ceases to be
significant anymore.

62

display cabinet

bass trap
speaker

low profile
equipment
rack

work bench

storage
cupboard

bookcase

low profile
equipment
rack

chair

storage
cupboard

bass trap

bass trap
speaker

chair

storage
cupboard

bookcase

bass trap
speaker

bookcase

entrance door

2 The addition of bass traps significantly tightens up

the low frequency response of the room, and large
curtains soak up live reflections from the upper end of the
frequency spectrum downwards. Thicker and heavier
curtains absorb frequencies further down the spectrum.

storage
cupboard

bass trap

storage
cupboard

bookcase

bookcase

entrance door

3 Finally, the addition of randomly varying hard

surfaces such as books and ornaments provides
quality diffusion for high frequencies. This restores the
feeling of air and space in the room without disturbing
the stereo imaging. This can be particularly effective
across the back wall of a room.

CM58.acoustics

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ACOUSTICS
fantasy. In reality, no rectangular minimalist room with
bare walls is a good listening environment. You need
to make creative use of your furniture to make your
room a more complex shape.
Be assured, however, that the sonic difference
made to a room by such simple additions can be truly
astonishing. For a simple example of suitable furniture
layout, see the first diagram in The Solutions
walkthrough on p62.

Testing your room

3

As a separate set of figures, do the same for
the length of the room (front to back) and for
the height (floor to ceiling).

4

Start the mda TestTone plug-in and switch it to
SINE mode. While listening to a tone of about
1kHz, adjust your speaker volume to a comfortable,
moderate listening level.

Taming the bass end
Ironically, a very solidly built room tends to have bass
problems. If your studio is made of flimsy stud walls,
excess bass leaks through to adjoining rooms. But in a
room made of brick or stone, bass frequencies tend to
gather at certain points in the room, and you will
notice a dramatic change in the amount of bass
depending on where you stand.
This can be very worrying. How can you determine
how much bass is right for your mix when you might
hear little bass in your normal listening position but
too much when you listen further back in the room?
We need to ‘mop up’ all of that excess bass and
make the sound more consistent throughout. Then
you’ll be hearing the real amount of bass, instead of
bass that’s over-amplified by your room.
We achieve this by placing bass traps in the room’s
corners. All you need to build them are some large,
solid wooden boxes stuffed with non-flammable
cotton wool or similar material. Such boxes are
available in the form of simple, cheap, display cabinets
without doors, or you can knock them up yourself
from offcuts of chipboard and a few nails. For stuffing,
you can buy very cheap pillows from your local
catalogue store. Feather pillows are even better, but
are more expensive.
Simply place units like this on the floor in the
corners of your room. Two are probably enough for
most small rooms. They tighten up the bottom end of
a room wonderfully. It might take you a while to get
used to the new sound!
If you want to improve the appearance of these
units, cover the entire box with a thin fabric – the
material used for covering the front of hi-fi
loudspeakers is ideal. You could tell your friends that
the entire unit is just an enormous subwoofer speaker
used only for dub reggae...
You don’t even have to use a dedicated unit as a
bass trap. If you are using tall, solidly-built, freestanding bookcases to help break up the shape of the
room, you can simply stuff pillows into the bottom
two shelves to achieve a similar, bass-damping effect
(though this will be less pronounced than units placed
in the corners of the room).

Controlling room reflections

5
Get your hands on the TestTone plug-in by pointing your
browser at www.mda-vst.com
You can perform a simple test to see if your room
suffers from resonance problems. You’ll need to
use the mda TestTone VST plug-in – available as a
pack of plug-ins for free download from
www.mda-vst.com.
This plug-in is just a simple test tone generator
which you can use to manually sweep through all
of the audio frequencies.
Before performing this test, however, you need to
observe some precautions, as sine wave testing
can damage your speakers if not done with a great
deal of care:
• Do not play very high or very low frequencies
through domestic-quality loudspeakers
• Listen only at a very moderate sound level –
quieter than normal music playback
• Do not leave the test tone running for extended
periods of time
• If you cannot hear the test tone, fix the problem
before turning the speaker volume up
The test is performed as follows:
Firstly, some maths: the speed of sound is
approximately 1,130 feet per second (at room
temperature). Divide this number by the width of
your room in feet to find the resonant frequency of
the side walls. For example, for a room 8.5 feet
wide: 1130/8.5=133Hz. Write down your answer.

1

2

As the room can also resonate at harmonic
intervals, write down several multiples of your
answer (ie, double, triple, four, five, six and seven
times your original answer. You don’t normally
need to go any higher than this).

Now, starting from a frequency of about 50Hz,
manually adjust the frequency – very slowly –
upwards to somewhere just above 1kHz. You don’t
need to go any higher, because this test becomes
much less valid at high frequencies. You need to do
this in several steps, using the F1 control on the
plug-in to set the frequency range, and F2 to
manually sweep through it.

6

As you sweep up the frequency bands, listen
carefully as you pass through the resonant
frequencies you’ve written down. If the volume
level of the tone seems to suddenly leap out at you
at around this frequency, you know you’ve got a
resonance problem that needs addressing. If you
pass cleanly through the numbers you’ve written
down, you’re in the clear.

7

It’s important not to get too obsessive when
using this test. Many minor variations in the
level of the tone will happen as you sweep; these
should be ignored.

8

You may notice other significant resonances as
you sweep through the low frequencies. It
may be the side panels of a wardrobe vibrating in
your room, or perhaps a flimsily constructed wall
where a cupboard was built into the room. You’ll
need to find creative solutions to fix such problems
such as these.

9

Listen out also for any rattles and buzzes from
objects within the room as you sweep
through the low frequencies. There may be several
different objects in the room that have been
rattling for ages – it’s just that you never noticed
them before.
The above method, though useful, is still a very
crude one that should never be used to fine-tune a
room – this technique is far too primitive for that.
It is, however, ideal for identifying when either the
room, or some object within it, is causing
significant and undesirable resonance problems at
low-to-mid frequencies.

It’s not just the bass frequencies that need to be
tamed, it’s the high frequencies too. But this time, the
problem is more complicated.
We need to prevent all direct reflections from

Ironically, a very solidly built room
tends to have bass problems. If
your studio walls are flimsy, excess
bass leaks to adjoining rooms
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Page 64

If you’ve got some spare ceiling
tiles lying around, you can improve
the absorption of the room by
mounting them on the wall

ALAMY

CM58.acoustics

Fire safety
It’s lovely to come home to a real fire – unless it
happens to be your studio burning down. Avoid
damage to equipment, friends and family by
following some sensible, basic fire precautions...
• Egg boxes and polystyrene blocks (once popular
home-made sound treatments in schools) can pose
a major fire risk because of their high flammability.
Stay well clear of these dangerous materials unless
they have been specially treated for fire safety.
• Anything that you attach to your ceiling must be
flame retardant. Horrific disco accidents in the
1970s demonstrated that flammable ceiling tiles
will rain down dozens of burning droplets of sticky
fire into people’s hair and onto their skin and
clothes. The consequences are terrifying.
• Whatever material you use to create curtains
lining your walls, make sure it’s flame retardant.
Because curtains are baggy, trap air and hang
vertically. They are one of the biggest fire risks in
any building.
• Wall-wart power supplies jammed into mains
distribution boards hidden behind a curtain are a
recipe for disaster if left unattended. Use a
separate mains outlet for items that absolutely
must be left turned on (such as VCRs) and supply
everything else from switched outlets so you can
turn off everything with just one or two mains
switches when your studio is not in use. Wallwarts can get dangerously hot in enclosed spaces
overnight, so beware.
• Bass traps can double as fire traps because of
their box-like construction. Make sure they are

64

stuffed with flameproof stuffing only. If in doubt
about the choice of stuffing, just use cheap pillows
certified to British Standards for Fire Safety in
Home Furnishings.
• Try to keep the escape route clear of cables. Use
longer instrument cables to go around the edge of
the room rather than taking a shortcut across the
path to the doorway. We’ve all tripped over our
own cables at some point; do you want that to
happen in the dark, during a night time fire when
the power has cut out?
• Buy a fire alarm and site it appropriately. They
only cost a few pounds and some local councils
even give them away for free. They are battery
operated and there’s no wiring involved – they
simply screw onto the ceiling in just a couple of
minutes. Experiment (using sticky tape) to find the
best location so that normal activities – like
smoking cigarettes (or anything else) – will not set
it off accidentally. Otherwise, someone will get
annoyed and take the battery out one day and
forget to put it back in.
• Buy a fire extinguisher suitable for ‘Class E’
(electrical) fires. Keep it accessible and clearly
visible. Do not buy a water-based extinguisher;
these are too dangerous in a studio that has
power supplies and mains boards everywhere.
Note that all modern extinguishers are simply
coloured red by law (they used to be available in
different colours, depending on the contents). The
new-style red extinguishers all sport a small
rectangular coloured label on the front that states
their true contents.

reaching our ears, but if we only do this, we end
up with an unresponsive room that feels
claustrophobic to work in. We need to create a more
diffuse reflection field.
But let’s start by removing those troublesome
direct reflections. The easiest way to do this is to hang
heavy curtains on the walls, but fitting conventional
curtains can be a very time consuming business. If,
like most of us here at CM, you’d prefer to spend your
time making music rather than sweating over a power
drill or spending hours threading curtain hooks, then
fear not – there is a simple curtain solution that can be
fixed up in a few minutes, and is suitable for most
small project rooms.
The solution is to use a shower rail or similar tube
to hang material from. There are cheap, spring-loaded
collapsible rails available that are adjustable to fit a
range of widths. A pair of these can easily span a small
room using either an existing roof beam or a small
block of wood between the two. Alternatively, a piece
of furniture like a wardrobe or tall bookcase can be
used to bridge the gap.
For longer spans, any kind of strong, inexpensive
tubing, such as wooden dowelling, can be used. You
only need simple supports at each end, and perhaps
some additional support along its length if it is
particularly long. We’d advise against trying to use
string or rope to hang your curtains from, as curtain
material is very heavy.
Using a simple rail for support in this way is quick,
easy and doesn’t require expensive ready-made fitted
curtains. You can still use pre-made tabbed curtains as
shown in the photographs, but any material could
easily be hung from the rail. Note that lightly coloured
curtains can be hard to keep clean if people smoke,
and curtains that are too dark can make a room feel
gloomy and sinister.
If you’ve got some spare ceiling tiles lying around
or have the cash to buy some, you can further
improve the absorption of the room by mounting
fireproof cork or polystyrene roof tiles directly onto
the wall, out of sight behind the curtain. However, this
is not absolutely necessary if the curtain material is
thick and heavy enough.
As shown in diagram 3 in The Solutions
walkthrough on p62, you don’t have to hang curtain
material around the entire wall; in fact, it’s better if
you don’t. By hanging heavy curtain only around the
section of room in front of your listening position, you
effectively create a sophisticated listening
environment known as the ‘Live End – Dead End’ (or
LEDE) control room.
The concept behind an LEDE room is to make the
front half of the room almost completely damped
down by heavy materials to keep the sound crisp and
dry, but allow the rear half of the room to reflect
sound in a relatively lively manner so as to represent a
more natural listening environment. The human brain
is capable of detecting that the reflected sound is
coming from behind you, so you can still concentrate

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ACOUSTICS

Creating a bass trap: get stuffed..

1 This simple display can be cannibalised for use as a
bass trap – its size is ideal.

2 We discard the quarter shelves, turn the unit
sideways, and stuff it with four pillows.

3 Then we simply leave it in the corner of the room. It’s
OK to place things on top, such as this CD rack.

Lining a room with curtains: and covering childish wallpaper..

1 Adjustable, sprung shower rails can be wedged
between walls without marking them.

on the uncoloured sound in front of you.
That’s the theory, anyway, and in practice this
arrangement really does seem to work. It’s used in
many top-flight recording studios around the world.
Technically speaking, a true LEDE room would typically
include a hard floor covering on at least part of the
rear section of the room, but at home, with a parallelfacing floor and ceiling, this might cause more
problems than it solves.
To further cut costs, you don’t even need to use
full-height curtains. An adequate length of curtain
hanging at ear-level at your normal listening position
may be all that is required, although it is obviously
more desirable to have a room where the sound
remains consistent regardless of whether you are
sitting or standing, and the less curtain you use, the
less absorption you will achieve.
Finally, in order to stop the room sounding as dead
as an anechoic chamber, we need to create a diffusion
or scatter wall to create complex secondary reflections
at the back of the room. Custom designed diffusion
walls are extremely expensive. However, most homes
(and that could include yours) already feature a scatter

2 Tabbed curtains or similar material is simply hung
from the railings.

wall even though you don’t know it yet – it’s our old
friend the bookcase again!
Bookshelves and bookcases are a remarkable boon
if you want to get a good-sounding room. Firstly, they
help break up a square or rectangular room, and –
more importantly in this case – they create a pseudorandom hard surface that causes high frequencies to
scatter on impact into many directions at once. This is
exactly the kind of behaviour we want.
You don’t need a floor-to-ceiling covering of books
(although there’s no harm in that). All that is needed is
a decent wall covering of books at ear level to diffuse
the sound. The more random the surface of books,
the better, so it’s time to get your books disorganised
and mix them up as much as possible so big and small
books intermingle in unpredictable ways.
The ideal placement for your scatter wall of books
is across the back of the room, although there is no
harm in having them down the sides as well. They
should be ideally positioned behind your normal
listening position though, so that sound from the
monitor speakers bouncing off them hits the back wall
before reaching your ears.

3 A roof beam can bridge the gap between two curtain
rails, or you can use a tall cabinet, as shown here.

Grand designs
As we’ve seen, probably the most versatile piece of
furniture you can place in your studio room is one or
more tall bookcases. The lower shelves can be stuffed
with pillows to act as a bass trap, the middle shelves
can be stocked with books of random sizes to act as a
diffuser wall, and the top shelves can be used, well, as
actual shelves to place your bits and pieces on.
But remember that before starting the process of
renovating your room, it’s best to design it on paper
and make sure you can get everything you need
within your budget (and within the physical space,
too). Test the sound of the room thoroughly by
listening to several well-known recordings before even
starting to make changes, so you know exactly which
of the problems we’ve discussed apply to your room.
Keep checking as you go along to find out how well
you’re progressing.
You’ll be surprised at how dramatically the sound
of the room improves as a result of the simple
changes we’ve described. And best of all, if
you’ve got a well-stocked home, you might be
able to do it without spending a single penny.
65

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