54 Bedrock SMxx operating manual © Bedrock Audio BV, 2019
55
Polarity measurements make use of test signals, usually saw-tooth wave patterns that either
rapidly rise or decline in level. A test signal is provided on the flashdrive bundled with the
SMxx and also available for download from the Bedrock audio website. The same test sig-
nal is featured on the BTB65 TalkBox (depending on the firmware version and production
date of the talkbox). This default test signal is a sawtooth with a slow incline and a rapid
descent and a period of 20 Hz. The module can also be configured for custom test signals,
with a user defined period and up/down characteristic.
The polarity module is a configuration aid only; it does not have options to save data as
most measurement modules do. The module is operated as follows:
• play the test signal continuously over the sound system under test
• start the measurement on the SMxx
• bring the measuring microphone up close to the loudspeaker (typically 0.5 to 1m, de-
pending on the acoustics of the room and the configuration of the loudspeaker). A
little experimentation may be needed to determine the optimal measuring distance.
• The module shows a + or - sign to indicate the signal polarity, alongside a graphical
representation of the loudspeaker cone movement in response to the test signal
• A graphical representation of the impulse response is also shown.
It can be difficult to obtain consistent readings for multi-way loudspeakers; it may be neces-
sary to measure op close to each of the drivers.
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