Wan-Ho Cho

Beamforming loudspeaker array in a multi-layered configuration

A planar, broadside acoustic array with uniform loudspeaker spacing is often adopted for generating a highly directional acoustic beam, but the performance in radiated power and spatial bandwidth should always compromise with the transverse size limit. To achieve a high-power, directional sound in a compact size, a multi-layered loudspeaker array configured in both broadside and end-fire types is devised. This design concept is tested with an array of 3 layers with 0.2 m spacing. Each layer contains 7 loudspeakers in a centrally symmetric arrangement on a plane with the longest dimension of 0.6 m. In each layer, the separation distance between loudspeakers is uniformly set as 0.2 m. The optimal beamforming method is employed for calculating the control filter. The compensation for the performance degradation due to self-scattering effect is also included in the control filter, for which the additional phase delay due to scattering is estimated from the simulated response of the array system. The maximum sound level at 1 m distance from the array center is achieved as 145 dB at 1.5 kHz, and, at 30 m position, the level decrease of 26–30 dB with the directivity index of 15 dB is observed for 1–5 kHz.A planar, broadside acoustic array with uniform loudspeaker spacing is often adopted for generating a highly directional acoustic beam, but the performance in radiated power and spatial bandwidth should always compromise with the transverse size limit. To achieve a high-power, directional sound in a compact size, a multi-layered loudspeaker array configured in both broadside and end-fire types is devised. This design concept is tested with an array of 3 layers with 0.2 m spacing. Each layer contains 7 loudspeakers in a centrally symmetric arrangement on a plane with the longest dimension of 0.6 m. In each layer, the separation distance between loudspeakers is uniformly set as 0.2 m. The optimal beamforming method is employed for calculating the control filter. The compensation for the performance degradation due to self-scattering effect is also included in the control filter, for which the additional phase delay due to scattering is estimated from the simulated response of the array system. The maximum s...

Modification of impact sound by adjusting the excitation input for comfortable design of punch press machine sound

The effectiveness of adjusting the excitation input as a method for modifying impact sound was investigated. The radiation from the impact can be described using a convolution of an impulse response function for a vibro-acoustic system and the corresponding impact excitation function. Therefore, the radiated sound can be changed by modifying both the impact excitation function and the structural response. Excitation with complicate shapes of input which is required to make an arbitrary shape of wave form, such as selective excitation or rejection of a specific frequency component, is not easy for manually operated traditional system. However, the modification of excitation input is useful for the automated system with an electrically controlled impactor, such as a servo-motor. As a practical application, a punching process of a punch press machine was designed to not only reduce the overall sound pressure level but also improve the perceived sound quality. Sound from a punch press can be improved by dividing the punching process into several steps with different stroke speeds without substantially reducing the cutting surface quality.

Evaluation of system configuration to check the suitability for the sound field rendering using the inverse approach

Sound field control by the inverse approach based on the acoustical holography is useful to render an arbitrary target sound field within a selected control zone if the target condition is given in a detailed format. This method needs information on the various factors constituting the total system: source array configuration, relative position of source and control region, assigning method of target field condition, conditioning method, etc. Because these factors heavily affect the accuracy of the generated sound field, a proper definition of the problem including all factors related to the system configuration is important. In this work, the method to evaluate the suitability of system to achieve the target sound field was investigated in the viewpoint of efficiency and precision. Because the difference between target and generated sound field strongly depends on the noise and the information error existing in the actual situation, the expected accuracy should be calculated in relation to the characteri...