Handbook for Sound Engineers

1628 Chapter 46

through a small loudspeaker (for testing microphones)
or an XLR connector (for testing electronic devices) and
a receiving device that collects the signal via an internal
microphone (loudspeaker testing) or XLR input jack. A
green light indicates correct polarity and a red light
indicates reverse polarity. The receive unit should be
placed at the system output (in front of the loudspeaker)
while the send unit is systematically moved from device
to device toward the system input. A polarity reversal
will manifest itself by a red light on the receive unit.

46.3.7.3 Impulse Response Tests

The impulse response is perhaps the most fundamental
of audio and acoustic measurements. The polarity of a
loudspeaker or electronic device can be determined
from observing its impulse response, Figs. 46-29 and
46-30. This is one of the few ways to test flown loud-
speakers from a remote position. It is best to test the
polarity of components of multiway loudspeakers indi-
vidually, since all of the individual components may not
be polarized the same. Filters in the signal path (i.e.,
active crossover network) make the results more diffi-
cult to interpret, so it may be necessary to carefully test
a system component (i.e., woofer) full-range for defini-
tive results. Be sure to return the crossover to its proper
setting before continuing.

46.4 Conclusion

The test and measurement of the sound reinforcement
system are a vital part of the installation and diagnostic
processes. The FFT and the analyzers that use it have

revolutionized the measurement process, allowing

sound practitioners to pick apart the system response

and look at the response of the loudspeaker, roo, or

both. Powerful analyzers that were once beyond the

reach of most technicians are readily available and

affordable, and cost can no longer be used as an excuse

for not measuring the system. The greatest investment

by far is the time required to grasp the fundamentals of

acoustics to allow interpretation of the data. Some of

this information is general, and some of it is specific to

certain measurement systems.

The acquisition of a measurement system is the first

step in ascending the capability and credibility ladder.

The next steps include acquiring proper instruction on

its use by self-study or short course. The final and most

important steps are the countless hours in the field

required to correlate measured data with the hearing

process. As proficiency in this area increases, the speed

of execution, validity, and relevance of the measure-

ments will increase also. While we can all learn how to

make the measurements in a relatively short time span,

the rest of our careers will be spent learning how to

interpret what we are measuring.

Figure 46-28. A popular polarity test set.

Figure 46-29. The impulse response of a transducer with

correct polarity.

Figure 46-30. The impulse response of a reverse-polarity

transducer.

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