An overview of directivity control methods of the parametric array loudspeaker

Abstract

A sound reproduction system usually consists of several types of loudspeakers to cater to sophisticated applications. The directivity of a loudspeaker is a measure of its efficiency in sending sounds to a particular direction instead of all directions. Demand to control the directivity of a sound reproduction system is gaining momentum with many new designs of directional loudspeakers, including the acoustic dome, horn loudspeaker, loudspeaker array, and parametric array loudspeaker (PAL). The PAL is an application of the parametric acoustic array in air, which generates a sound beam from the interaction of ultrasonic beams. The PAL has several desired features, such as its narrow beamwidth over a wide frequency range, low sound attenuation over a long distance, and ability to reproduce perceptually near sound images. The PAL is also advantageous in using a smaller driving unit to transmit an equally narrow sound beam as compared to the conventional loudspeaker and broadside loudspeaker array. An overview of directivity control methods of the PAL is presented in this paper. In particular, acoustic models and signal processing techniques in controlling the directivity of the PAL are emphasized.

Reproducing personal sound zones using a hybrid synthesis of dynamic and parametric loudspeakers

“…Earlier models include Westervelt's directivity (WD) [13] and product directivity (PD) [23], [24], though, these models do not accurately match measured directivity from a PL. Recently a convolutional directivity (CD) model, used in this work, was proposed [12], [25] utilising both WD and PD which has better correlation to measured directivity.…”

“…The CD is defined as the convolution between the PD and WD with the linear convolution operator, * , as [12], [25] (12) where k c is the ultrasonic carrier frequency, D G x,k is the Gaussian directivity [24] …”

“…PLs, on the otherhand, are capable of providing high directivity at high frequencies [12] and were first theorised in 1963 [13]. PLs have gained interest due to their high directivity with a relatively small physical size which is comparable to dynamic (conventional) loudspeakers.…”

“…Practical implementations have shown PLs can provide immersive spatial audio [14], [15], however, neither of the hybrid approaches use MSR with dynamic loudspeakers or consider spatial aliasing. When comparing PLs to MSR from dynamic loudspeakers, PLs lack directivity at low frequencies [12], contain higher Total Harmonic Distortion (THD) [2], [16] and can have potential health risks due to the high Sound Pressure Level (SPL) of the ultrasonic carrier frequency [2].…”

Robust sound image localization for moving listener with curved-type parametric loudspeaker

“…One potential solution to this, using a motor for steering the direction of the parametric loudspeaker in keeping with the movement of the listener, is problematic because the driving sound may create noise. Moreover, other methods which utilize a signal processing have also been proposed for steering the beam direction [8]. These methods however is difficult to continuously steer the direction.…”