100 Bedrock SMxx operating manual © Bedrock Audio BV, 2019
101
The aim of these tests is to verify that the electro-acoustic front end of the measuring sys-
tem is within specifications. The instructions assume that the instrument under test is a
Bedrock SMxx device.
Item Goal Check
Level accuracy - Start RTA module.
- Place microphone tip in tone calibrator (B&K 4231, Bed-
rock BAC1, Bedrock BAC2 or Cirrus CR:515.)
- Select 1000 Hz band with the cursor in the RTA module.
- Measure during 8 seconds.
- The level at 1000 Hz must match the calibrator refer-
ence value (usually 94 dB) +/- 0.5 dB.
Acoustic linear-
ity
- Press +10 dB button on calibrator. Level in RTA module
@ 1000 Hz must rise by 10 +/- 0.4 dB
Flatness - Remove the microphone and pre-amplifier, and connect
the line-out of a Bedrock BTB65 Talkbox to XLR input
into SMxx, through attenuator set at 20 dB. The level into
the XLR input of the SMxx will be approx. -32 dBU.
- Select “pink noise” on talkbox.
- In RTA mode, set blue channel to LZEQ
- Check bands with cursor. All 1/3 octave bands in the
range 100 Hz- 12.5 kHz must lie within + 3 dB of the
value at 1000 Hz.
Linearity - Set attenuator at 40 and 60 dB (resp. -52 and -72 dBU).
A-weighted level must reduce by the attenuation setting
+/- 0.4 dB
STIPA test - Set attenuator at 40 dB (input level to the SMxx approx.
-52 dBU).
- Open the STIPA pro module.
- Play that STIPA signal from talkbox (line out unmuted).
- Run STIPA measurement until finished (25s)
- STI must be at least 0.98
- Go to measurement details screen in the STIPA pro
module.
- column “Rel” must show only values between -2.0 dB
and +1.0 dB.
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