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The Importance of Studio
Broadcast Engineering, April
1, 2005 by Ken C. Pohlmann
The frequency response of a power amplifier will
be the same in your audio control room as it was
on the test bench. Grounding and shielding issues
aside, an amplifier's performance does not depend
on its environment or location. On the other hand,
the frequency response and many other performance
criteria of microphones and loudspeakers are affected
by the room they are in. Indeed, specifications
of transducers have limited value because they cannot
account for the real-world conditions of their use.
The acoustics of any room can profoundly affect
the quality of any audio signal that is acoustically
conveyed in that room. Whether you are recording
voice or music into an open microphone, or monitoring
or mixing over loudspeakers, the room can dictate
what is recorded and what you think is recorded.
For that reason, any serious studio needs serious
First and foremost, any studio must be quiet. Ambient
noise will ruin an acoustic recording, or potentially
mask detail in a mixdown. Acousticians use a Noise
Criterion (NC) rating to determine the noise floor
in a room. The NC uses Sound Pressure Level measurements
at nine frequencies and fits the resulting curve
against standard curves. For example, an NC-15 rating
allows an SPL level of 36dB at 125Hz and 17dB at
1kHz. Ratings above NC-20 will be problematic for
most audio work. If your NC is too high, you need
to take measures to reduce it.
Generally, source treatment is the most effective.
Find out where the noise is coming from, and attack
it there. For example, turbulence noise from air
vents might be reduced by removing the vent's louvers.
If footsteps in the room above yours are audible,
generously offer to buy padded carpet for them.
Low-frequency rumble from an air conditioner can
be reduced by isolating the unit from the structural
slab it sits on. If source treatment is impossible
or not effective enough, you can try isolation techniques
to block the noise. For example, use solid-core
doors instead of hollow-core doors, replace single-pane
glass with double-pane glass, and make door seals
airtight to prevent sound from leaking around the
In a worst-case (biggest budget) scenario, you may
have to build new partitions to increase isolation.
A partition's acoustical stopping power is measured
by its Transmission Loss (TL). For example, if a
partition has a TL of 50dB, then an incident sound
of 80dB will be reduced to 30dB as it passes through
the partition. It is true that heavy, massive partitions
(such as concrete) provide good sound isolation.
But, lightweight partitions (such as staggered stud
walls) can also be effective. Also, consider what
frequencies you need to stop. Low frequencies are
hard to isolate, and a music studio might require
a concrete wall. But a voice-over studio might only
need a stud wall and a microphone with a low-cut
Isolation is critical, but room treatment is just
as important. Even a quiet room will be unsuitable
if its acoustics are wrong. For example, speech
intelligibility is poor in a reverberant locker
room. A room's reverberation time, measured as RT60,
is the time it takes for an initial sound to decrease
by 60dB. There is no "correct" reverberation
time. A too-long reverberation time will mask detail,
while a too-short reverberation time will sound
unnatural. Very generally, a ballpark time of one-half
to one second is about right for many music studios,
while a shorter time of less than one-quarter second
is better for voice-over studios.
Reverberation time is governed by absorption. The
more absorption, the lower the reverberation time.
The easiest way to add absorption is with porous
absorbers. Sheets of acoustical foam placed on otherwise
reflective surfaces can be added until reverberation
time is suitably reduced. Conversely, removing absorbing
materials lengthens reverberation time. This might
be the ideal excuse to get rid of a ratty old sofa
in your control room.
Sound quality is also affected by the way sound
reflects from surfaces. A flat reflective wall will
give a specular reflection, potentially yielding
an echo, or perhaps a kind of "acoustic glare."
Placing absorption on the surface would address
the problem, but it would also decrease reverberation
In small rooms, low frequencies are hardest to tame.
Room modes, areas of relatively high and low energy
in the room due to reflections from the room surfaces,
will yield an uneven frequency response that is
inconsistent throughout the room. One solution is
the addition of bass traps, which are large hollow
tubes filled with absorption, large blocks of acoustic
foam or wall-mounted panel absorbers. These will
help smooth bass response.
It's also worth noting that sound absorbers are
generally poor isolators. If you are bothered by
mechanical noise from an adjoining machine room,
putting acoustical foam on your wall won't help.
Alternatively, putting foam in the machine room
might lower its ambient levels a bit, and thus lower
the intrusion level into your room.
If an existing workplace has minor acoustical problems,
some common-sense solutions are worth trying. Simple
noise source treatment and absorbers and diffusers
can do wonders. For major problems, it is more cost-effective
to hire an acoustician to advise you. When it comes
to walls and floors, wrong decisions can cost you
dearly. Get it done right the first time. If you
are lucky enough to be planning construction of
a new facility, then an acoustician is an absolute
must. Many architects are geniuses, but many are
not skilled in acoustics; you'll need both an architect
and an acoustician. For the latter, talk to the
acoustician's past clients and even tour their facilities
to make sure the sound quality of the design is
The quality of your acoustical audio work is only
as good as the room's acoustics. Frankly, in today's
digital era, anyone with a modest budget can set
up a recording and mixing studio with electronics
that are as good or better than your professional
gear. The important difference between spare-bedroom
audio and professional audio is the acoustical quality
of a professional room.
You can do things a bedroom studio can't. You can
make an acoustic recording or a mix and ensure that
the recording is clean and accurate. If your studio
is not up to acoustical code, then you might offer
no technical advantage over the bedroom studio.
Good studio acoustics is thus supremely important
in keeping your work professional.
About the Author
Ken Pohlmann is director of the Music Engineering
Technology program at the Frost School of Music
at the University of Miami.
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