Method for measuring the low-frequency sound power from a complex sound source based on sound-field correction in a non-anechoic tank

Abstract

Similar to air reverberation chambers, non-anechoic water tanks are important acoustic measurement devices that can be used to measure the sound power radiated from complex underwater sound sources using diffusion field theory. However, the problem of the poor applicability of low-frequency measurements in these tanks has not yet been solved. Therefore, we propose a low-frequency acoustic measurement method based on sound-field correction (SFC) in an enclosed space that effectively solves the problem of measuring the sound power from complex sound sources below the Schroeder cut-off frequency in a non-anechoic tank. Using normal mode theory, the transfer relationship between the mean-square sound pressure in an underwater enclosed space and the free-field sound power of the sound source is established, and this is regarded as a correction term for the sound field between this enclosed space and the free field. This correction term can be obtained based on previous measurements of a known sound source. This term can then be used to correct the mean-square sound pressure excited by any sound source to be tested in this enclosed space and equivalently obtain its free-field sound power. Experiments were carried out in a non-anechoic water tank (9.0 m × 3.1 m × 1.7 m) to confirm the validity of the SFC method. Through measurements with a spherical sound source (whose free-field radiation characteristics are known), the correction term of the sound field between this water tank and the free field was obtained. On this basis, the sound power radiated from a cylindrical shell model under the action of mechanical excitation was measured. The measurement results were found to have a maximum deviation of 2.9 dB from the free-field results. These results show that the SFC method has good applicability in the frequency band above the first-order resonant frequency in a non-anechoic tank. This greatly expands the potential low-frequency applications of non-anechoic tanks.

Evaluation Method for Underwater Ultrasonic Energy Radiation Performance Based on the Spatial Distribution Characteristics of Acoustic Power

“…The half-power angle corresponds to when the radiated sound power of a sound source in the horizontal or vertical plane is reduced to half of its maximum value and, as such, it can reflect the directionality of the radiation of the sound source: in other words, the smaller the radiation angle of the sound source, the more obvious the directionality and the higher the energy concentration [ 24 ]. The advantage of the half-power angle evaluation method lies in its simplicity; however, it fails to fully consider the sound source’s radiation pattern and the radiation field’s distribution characteristics, cannot reflect the inhomogeneity of the radiation of the sound source, and can only calculate the value related to the main lobe [ 25 , 26 ]. Acoustic radiation force evaluation methods suffer from computational difficulties, with controversies and uncertainties regarding the force’s calculation and properties [ 25 ].…”