Zhong Jiaxin, Kirby Ray, Qiu Xiaojun
Centre for Audio, Acoustics and Vibration, Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, New South Wales 2007, Australia.
J Acoust Soc Am. 2021 Mar;149(3):1524. doi: 10.1121/10.0003606.
The near and far fields of traditional loudspeakers are differentiated by whether the sound pressure amplitude is inversely proportional to the propagating distance. However, the audio sound field generated by a parametric array loudspeaker (PAL) is more complicated, and in this article it is proposed to be divided into three regions: near field, Westervelt far field, and inverse-law far field. In the near field, the audio sound experiences strong local effects and an efficient quasilinear solution is presented. In the Westervelt far field, local effects are negligible so that the Westervelt equation is used, and in the inverse-law far field, a simpler solution is adopted. It is found that the boundary between the near and Westervelt far fields for audio sound lies at approximately a/λ - λ/4, where a is transducer radius and λ is ultrasonic wavelength. At large transducer radii and high ultrasonic frequencies, the boundary moves close to the PAL and can be estimated by a closed-form formula. The inverse-law holds for audio sound in the inverse-law far field and is more than 10 meters away from the PAL in most cases. With the proposed classification, it is convenient to apply appropriate prediction models to different regions.
传统扬声器的近场和远场是根据声压幅值是否与传播距离成反比来区分的。然而，参量阵扬声器（PAL）产生的音频声场更为复杂，本文提出将其分为三个区域：近场、韦斯特维尔特远场和反平方律远场。在近场中，音频声音会经历强烈的局部效应，并给出了一种有效的准线性解。在韦斯特维尔特远场中，局部效应可忽略不计，因此使用韦斯特维尔特方程，而在反平方律远场中，则采用更简单的解。研究发现，音频声音的近场和韦斯特维尔特远场之间的边界大约位于a/λ - λ/4处，其中a是换能器半径，λ是超声波波长。在换能器半径较大且超声频率较高时，边界靠近PAL移动，可用一个闭式公式估算。反平方律适用于反平方律远场中的音频声音，在大多数情况下距离PAL超过10米。采用所提出的分类方法，便于将适当的预测模型应用于不同区域。
