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Reverberation Time Meter (RT60)
The reverberation time (or RT60) is among the most commonly specified acoustic
measures. Unfortunately, reverberation time measurements are also among the most
complex to carry out accurately. RT60 measurements are prone to errors, which cannot
always be detected by the measuring device.
If you are new to measuring reverberation times, we recommend that you read
this section of the manual carefully, and preferably also consult external literature
and training materials on reverberation time measurements.
Standardized procedures for measuring the reverberation time of a room are specified in
ISO-3382-2. Generally speaking, there are two different ways to measure RT60: the impulse
response method and the interrupted noise method. Both methods are standardized through
ISO-3382-2.
The impulse response method uses a carefully controlled, known test stimulus of short
duration (sweeps, chirps, pseudo-noise sequences or gunshot-like impulsive sounds). By
normalizing the recorded sound in a room relative to the source signal, the impulse
response of the room is obtained. From this impulse response, the RT60 is calculated. The
impulse response method is currently not supported by the VOX-01. Of the two available
methods, it is more likely to produce invalid results for the following reasons:
•
The impulse response method requires that very specific, known test signals
are used. Any difference between the test signal that was really used on the
one hand, and that test signal that the measuring instrument expects on the
other hand, may produce greatly distorted results.
•
Depending on the type of test signal, even the slightest movement of the
microphone during the test may render the measurement inaccurate. The use
of a tripod is absolutely necessary.
The interrupted noise method, as supported by the VOX-01, measures the decay of the
sound field if a sound source is suddenly switched off. This method is more robust
against slight inaccuracies or inconsistencies in the placement of sound source and
microphone. In small rooms, no other tools than the VOXBOX talkbox and the VOX-01
may be needed. In larger rooms, a larger (spherical) loudspeaker and amplifier will be
needed. Either way, the procedure requires the following steps to be taken in preparation:
•
Place a source of continuous sound (preferably pink noise) in the room for
which the RT60 needs to be measured.
•
Place the VOX-01 at some distance from the source (stay clear from walls
and other flat surfaces)
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VOX -01 Operating Manual
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