Recording - November 2015 - 28

5. Bass waves need room to "develop"
This one is common in recording tutorials, often in the context of miking up a bass
amp or a kick drum. They will discover that
moving the microphone back (or forward!)
several inches or even a few feet will dramatically change the amount of low end

Figure 3. BassLab Studios in Salt Lake City is an outstanding example of a wonderful sounding room using parallel walls,
and no wood on the walls or ceiling (the wood floor is fully damped). The fact that it is built inside shipping containers
makes it even cooler. Photo by Steven Comeau, used with permission.
picked up by the microphone. In addition,
wavelengths for low frequencies are very
long, measured in feet (for instance, the
low E of a bass guitar is 41 Hz, which has
a wavelength of more than 27.5 feet).
People therefore conclude that you have
to be a certain distance away from a
sound source to perceive the low end. This
conclusion is demonstrably false; if it were
true then it would be impossible to hear
bass in headphones, when the drivers are
just an inch or two from your eardrums.
So what accounts for the microphone
phenomenon described above? Why,
when you move a mic back, does the low
end often get louder? The answer is for the
same reason that bass trapping is so
important. As bass waves move around
the room and reflect from surfaces, they
start to interfere with one another, creating
peaks and nulls relative to the frequency
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RECORDING November 2015

of the wave, and the position of everything involved (the kick drum or bass cabinet speaker, the mic, and nearby walls/
floor/ceiling). When you move a mic and
the bass gets louder, it means that you are
moving the microphone out of a null point
of the room, relative to the frequency the
bass is playing.
This is one area where a good understanding of room acoustics can really help
a recording engineer. For instance, not only
can you get better bass sounds by taking
advantage of null points, but you can also
place microphones for other instruments
(such as vocals, which don't have much low
frequency content) in the room at null points
for the bass, to reduce the amount of bass
bleeding into the microphone.
Spend some time experimenting with
these principles; once you get the mikedup bass amp sounding really good, have

your bassist play while you move the
vocal mic around the room. You'll find a
place where the bass is softer; if you can,
set the vocalist's mic up there. Aim the null
points of the polar patterns (for cardioid
or figure-8 mics) toward sounds you don't
want to record for even greater isolation.
6. Bass traps must be 1/4 wavelength
thick to be effective
This is another idea that people might
encounter as they dive more deeply into
room acoustics. I have even heard this from
several well-known studio designers or
acousticians. It is rooted in truth, and perhaps
contains more truth than some of these myths.
For instance, it is certainly true that a thicker
bass trap or absorber will perform better at
low frequencies, all else being equal.
But think about this for a moment. In the
above example (Myths 2 and 5), we

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