Apple Impulse Response Utility - Manual (Page 23)

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Microphone and Speaker Suggestions
The impulse response of a space is never just the space’s impulse response. The
recorded impulse response is always the response of the complete system—in other
words, every piece of equipment you use in the recording process. This includes, in
signal-flow order: the digital-to-analog converter, the amplifier and speakers (or
powered speakers), the room characteristics, the microphone(s), and finally the
microphone pre-amp and analog-to-digital converter. So, before leaving your studio to
do any location recording, you have to think about your equipment. These days, even
budget converters offer acceptable quality, so your main concern will be your selection
of speakers and microphones.
Speaker and Microphone Selection Suggestions
There are no rules as to which brand or make of microphone or speaker will result in
the best impulse response. A general guideline is to try using speakers and
microphones with a flat response (in other words, the speakers and microphones
should offer a very even signal at all frequencies). You can find microphones and
speakers that offer relatively flat responses at nearly all budget levels. Tube
microphones, which are generally valued for the tonal “color” that they add to the
signal, are not necessarily the best choice for recording impulse responses. In general,
microphones that work well as ambience mics are good candidates.
Speaker and Microphone Placement Suggestions
Where you place your speakers and microphones in the recording space will have a
large impact on the specific echoes and reflections that your impulse response
captures. It goes without saying that creativity is key, and experimentation the name of
the game!
There are, however, some general suggestions and guidelines that may help when
you’re first starting out.
One general suggestion for placement in environments with hard floors, made from
materials such as concrete: You may find that a “chirp” is recorded at the beginning of
your impulse response. This sound is actually the generated sine sweep coming
through the floor into the microphone. The speed of sound through floors and
concrete material is much faster than through air, resulting in a pre-impulse response
that starts before the impulse response you actually want to record. To get around this
potential problem, you can use “studio” drum pedestals and specialized microphone
mounts that have strong acoustic absorbers built into them. If you can’t carry around
pedestals, or afford expensive microphone mounts, try a thick carpet under the
speakers and microphone stand(s).