Parametric loudspeaker—characteristics of acoustic field and suitable modulation of carrier ultrasound

Abstract

Due to the inherent nonlinearity of the medium, finite amplitude ultrasound interacts with itself and generates some secondary waves in the sound beam. The parametric loudspeaker, making use of this phenomenon, has a sharp directivity and might be applied to a speech transmission system under the limited environment. In this paper, a numerical analysis method available for high sound pressure levels, where the nonlinear interactions of ultrasound become greatly active, can be used successfully to theoretically design the parametric loudspeaker. It is reported that the numerical computations agree well with the experiments by a circular aperture projector of radius 21 cm and carrier frequency 27 kHz. To develop the parametric loudspeaker for practical uses, the problems on harmonic distortions and the physiological effect on human being must be solved. Based on the theoretical prediction, the reasonable solutions for such problems are considered in accordance with appropriate primary wave modulations.

Experimental Evaluation of Distortion in Amplitude Modulation Techniques for Parametric Loudspeakers

“…However, due to the tone difference between the upper (USB) and lower band (LSB), the second harmonic is also louder. A simple solution to reduce the second harmonic is to transfer the energy to a single band as in the single side band amplitude modulations (SSBAM) [28], which are named LSBAM for the lower or USBAM for the upper sideband. This modulation can be obtained by using high-pass, low-pass filter or adding a quadrature term to the conventional AM.…”

“…A simple solution to reduce the second harmonic is to transfer the energy to a single band as in 24 the single side band amplitude modulations (SSBAM) [28], which are named LSBAM for the lower The BHX microphone is considered suitable for evaluating predistortion techniques in view of the results shown in Figures 3 and 4 as well as the usable range of frequencies of the ultrasonic speaker. The rest of the measurements detailed in this article are performed with this microphone.…”

Generating dual beams from a single steerable parametric loudspeaker

“…the notable harmonic distortion [10] and relatively weak bass output [11]. Research works on preprocessing methods have been extensively carried out to address the harmonic distortion [12][13][14][15]. On the other hand, the bass output of the parametric loudspeaker is an inevitable result of the parametric acoustic array.…”

Identification of the parametric array loudspeaker with a volterra filter using the sparse NLMS algorithm

“…For this reason, there have been many preprocessing methods to suppress the nonlinear distortion of the PAL [4][5][6][7]. The audio bandwidth extension has been attempted to improve the perceptual sound quality of the PAL [8,9].…”