Assessment and optimization of sound reproduction in water filled tanks

Examensarbete för masterexamen
Sound and vibration (MPSOV), MSc
Kindbom Jonsson, Axel
Many marine biological tests have been carried out in water-filled tanks where the area of research has been the effects of noise on aquatic life. Recorded or artificial noise has then been produced using loudspeakers, hydrophones, and various other noise sources. The desired sound spectra and sound levels are however hard to produce in the tank, and the sound field that gets produced can deviate largely from the desired sound field in certain or for all frequency regions. Techniques for a more accurate reproduction of sound fields in water-filled tanks thus have the potential to facilitate valid research about the influence of certain sound fields on marine animals. This report assesses the use of shaker excitation as a means for producing a desired sound field in water-filled tanks. In addition to this, it assesses the use of basic signal processing algorithms to equalize the sound field in the tank. A glass tank filled with 240 litres of water is used for the experiments, and the performance of the shaker is compared to the performance of an underwater loudspeaker. The performance of the signal processing algorithms is evaluated based on a comparison between the sound field with equalization applied to it, and the sound field when no equalization is applied to it. An existing analytical model is deployed to approximate the sound field distribution in the tank, and to communicate it graphically. The findings in this thesis suggest that the use of shakers as a means of excitation provides sound fields in the tank that are comparable with the sound field produced by an underwater loudspeaker. In terms of level in low frequency regions, the shaker is able to produce higher levels than the underwater loudspeaker. In combination with digital signal processing equalizing techniques, the performance of the transducer, being either the shaker or the loudspeaker, improves.
acoustics, equalization, shaker, excitation, underwater, marine, tank, pressure, velocity, signals
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