10
4.1.3
Selecting the Microphone Spacer
Click on the “Mic Spacer” button.
The microphone spacer is an important part of the sound intensity measuring technique using a
pair of microphones. Separated by a distance, the two microphones can measure the sound
particle velocity by using the pressure gradient. However for this estimation to be right, the
separation distance must be adapted to the wavelength. The following table shows the different
spacers and their associated bandwidth relative to the degree of precision:
Laboratory
Expertise
Control
Probe Intensity Response (H-F Limit)
< 1 dB
< 2 dB
< 3 dB
Pressure Residual Intensity Index (L-F. limit)
> 15 dB
> 12 dB
> 9 dB
12.5 mm
200Hz – 5kHz
100Hz – 6.3kHz
50Hz – 8kHz
25 mm
100Hz – 2.5kHz
50Hz – 3.15kHz
25Hz – 4kHz
50 mm
50Hz – 1.25kHz
25Hz – 1.6kHz
12.5Hz – 2kHz
Only the selected bandwidth is considered during the measurement. Hence, only the bands
located in the selected spectrum region will be calculated. Also, the Global levels (A, C and Z) will
be computed on this reduced bandwidth using a band-pass filter.
To cover a wider range, it is recommended to perform two measurements using two different
spacers.
