Recently, technologies for reproducing a 3dimensional sound field are required for providing highly realistic sensations. Therefore, we previously proposed a system with multiple parametric array loudspeakers (PAL). PALs can design sound images on walls, ceilings, and floors by using the higher directivity of ultrasound. Thus, the proposed system can easily present incoming sound from various directions. However, it is difficult to provide a realistic sensation depending on the reverberation time. In addition, the listening area of one PAL is small. In this paper, we therefore propose two approaches for overcoming these problems. First, we propose reverberation steering with indirect electrodynamic loudspeakers and PALs. We also attempt to expand the listening area of the sound image with a curved-type PAL. As a result of evaluation experiments for each proposed approach, we could confirm the effectiveness of each approach.
A parametric loudspeaker which utilizes the ultrasound can transmit the audible sound to a particular area. However, the sound reproduced by a parametric loudspeaker contains the harmonic distortions because the sound is demodulated by the nonlinearity in the air. Thus, measuring the harmonic distortions is required to evaluate the sound quality of a parametric loudspeaker. Measurement with a sine wave has used as the method to measure harmonic distortions. The harmonic distortion is measured by analyzing the integral multiplication frequency of a reproduced sine wave. Many measurements by using sine waves with each different frequency are required to measure the wideband harmonic distortions. Therefore, measuring the wideband harmonic distortions with sinusoidal wave method requires much more time. Recently, using Log-TSP (Logarithmic-Time-Stretched Pulse) signal was proposed to measure the wideband harmonic distortions in a short time for electrodynamic loudspeakers. Thus in this paper, we attempt to measure harmonic distortion of a parametric loudspeaker by using Log-TSP signal. We carried out an objective evaluation experiment in a soundproof room. The result by using Log-TSP signal was compared with that by using sinusoidal wave method. As a result, we confirmed the result with Log-TSP is equivalent to that with sinusoidal wave method.
A parametric loudspeaker has a high directivity by utilizing an ultrasound wave as a carrier wave. Therefore, a parametric loudspeaker can form a specific listening spot called “audio spot.” Furthermore, a parametric loudspeaker can form the “reflective audio spot” by utilizing the reflected sound. The listeners in the listening area may perceive the acoustic sound image on the reflector. However, it has the problem that the reflective audio spot with a single parametric loudspeaker is narrow area. Therefore, it is difficult for several listeners to perceive the reflective audio spot at the same time. If we can expand the area of the reflective audio spot, several listeners can perceive the reflective audio spot at the same time. Thus. in this paper, we attempt to steer the area of the reflective audio spot with parametric loudspeaker array. We carried out objective and subjective evaluation experiments to confirm the effectiveness of the proposed system in a conference room. As a result, we confirmed the proposed system can expand the are of the reflective audio spot.
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