46 Bedrock SMxx operating manual © Bedrock Audio BV, 2019
47
It is good practice (and a formal requirement for many applications) to average across as
many measurements as needed to obtain a green cross next to all relevant frequency bands.
Never rely on results from RT60 measurements until you have checked the re-
ported status per individual frequency band. Note that in some rooms it may
be difficult, if not impossible, to obtain reliable results for the lowest frequency
bands.
Please take note of the following practical tips and pointers for RT60 measurements:
• Do not place the measurement microphone and noise source too close to
each other; if possible, estimate the reverberation radius in the room, and
make sure that the microphone is as far outside the speaker’s reverberation
radius as possible.
• When using the interrupted noise method, make sure that your noise
source is capable of producing levels far above the ambient noise floor in
the room, and above the electronic noise floor of the device. Ambient levels
of 90 dB(A) and higher are often needed. The SNR must be at least 50
dB in all relevant frequency bands. A spherical loudspeaker configuration
playing pink or white noise is the preferred source of measurement noise.
If you are using a single, non-spherical loudspeaker, avoid placement of the
microphone on the loudspeaker axis. Even though the microphone is om-
nidirectional, avoid pointing the microphone straight at the loudspeaker.
• When using the impulse response method, use a starter gun or “clapper”
that is capable of producing high level impulsive sounds.
• Eliminate sources of background noise.
• The state of all doors, windows and other separations should be fixed (open
or closed) throughout the measurements. The opening of doors and win-
dows changes the reverberation time.
• Do not walk around when the measurement is running, especially not in
the immediate surroundings of the noise source.
• The signal-to-noise ratio requirements for RT60 measurements are some-
times difficult to meet. Especially for T30 measurements, it may be neces-
sary to play back the test stimulus (interrupted noise) at high sound pres-
sure levels.
• If your signal-to-noise ratio is insufficient for reliably measuring the higher
frequency bands, consider switching over to white noise (instead of the
commonly used pink noise) as a source stimulus.
If you are having trouble getting acceptable measurement data (green balls with check
marks next to your measurement data), it may help to study the exact reasons why your
measurement data is marked for rejection.
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