Handbook for Sound Engineers

Microphones 579

mount suspensions allow a microphone to stay still
while the support moves.
Suspensions all use a springy arrangement that
allows the microphone to be displaced and then exerts a
restoring force to return it to the rest point. It will inevi-
tably overshoot and bounce around, but the system
should be damped to minimize this.
As frequency lowers, the displacement wavelength
increases so the suspension has to move farther to do
the job. For any particular mass of microphone and
compliance (wobbliness) of suspension, there is a
frequency at which resonance occurs. At this point the
suspension amplifies movement rather than suppresses
it. The system start to isolate properly at about three
times the resonant frequency.
The microphone diaphragm is the most sensitive
along the Z-axis to disturbances. Therefore the ideal
suspensions are most compliant along the Z-axis, but
should give firmer control on the horizontal (X) and
vertical (Y) axes to stop the mic slopping around,
Fig. 16-170.

Suspension Compliance. Diaphragm and so-called
donut suspensions can work well, but tend to have
acoustically solid structures that affect the microphone’s
polar response. Silicone rubber bands, shock-cord cat’s
cradles, and metal springs are thinner and more acousti-
cally transparent but struggle to maintain a low tension,

which creates a low resonant frequency, while at the

same time providing good X–Y control and reliable

damping. The restraining force also rises very steeply

with displacement, which limits low-frequency

performance.

Shock mounts may be the type shown in Fig. 16-168.

This microphone shock mount, a Shure A53M, mounts

on a standard in – 27 thread and reduces mechanical

and vibration noises by more than 20 dB. Because of its

design, this shock mount can be used on a floor or table

stand, hung from a boom, or used as a low-profile stand

to place the microphone cartridge close to a surface

such as a floor. The shock mount in Fig. 16-169 is

designed to be used with the Shure SM89 shotgun

microphone.

Shock mounts are designed to resonate at a

frequency at least 2½ times lower than the lowest

frequency of the microphone.^21 The goal is simple but

Figure 16-167. Reflexion Filter. Courtesy sE Electronics.

Figure 16-168. Shure A53M shock mount. Courtesy Shure

Incorporated.

Figure 16-169. Shure A89SM shock mount for a shotgun

microphone. Courtesy Shure Incorporated.

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