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Measuring assembly for testing the influence of mechanical vibrations on sound level measurements

10.10.2006

To check the vibrational sensitivity of sound level meters, a measuring assembly has been set up in which two identical sound level meters are exposed simultaneously to a sound field of constant frequency.

Mechanical vibrations of the floorspace which, during the measurement, affect the sound level meter via a tripod can have an influence on the measuring value displayed. Especially vibrations along the main measuring direction of the microphone cause a mechanical stimulation of the microphone and a considerable reduction of the linear measuring range at low levels. To check the vibrational sensitivity, a measuring assembly has been set up in which two identical sound level meters are exposed simultaneously to a sound field of constant frequency. The displayed A–rated values of both meters are compared with each other while one of the two meters is stimulated by an electro-dynamic shaker to vibrate at an acceleration of 1 m/s². The stimulation is applied in two directions: (1) vertically in the direction of minimal microphone sensitivity (Fig. 1), and (2) at an angle of 90° in the most sensitive direction. The frequency of the stimulation varies between 31.5 Hz and 1 kHz. The result of the measurement shows the shift of the lower working range limit under conditions of mechanical vibration.

Vibrational stimulation of a sound level meter in vertical direction. The value displayed for the sound pressure level L<sub>p</sub> is compared to the value of the reference meter.

Figure 1: Vibrational stimulation of a sound level meter in vertical direction. The value displayed for the sound pressure level Lp is compared to the value of the reference meter.

Contact person:

Ingolf Bork, FB 1.7, AG 1.72, ingolf.bork@ptb.de