An omnidirectional parametric loudspeaker (OPL) is a sound source that is made of hundreds of ultrasonic piezoelectric transducers set on a sphere. Relying on the parametric acoustic array (PAA) phenomenon, each transducer emits an ultrasonic carrier beam modulated by an audible signal. Thanks to non-linear propagation in air, natural demodulation takes place and focused audible beams are obtained. An OPL thus emits hundreds of audible sound beams in all directions. In this work, the performance of an OPL prototype containing 750 transducers set on a sphere of radius 0.125 cm is examined in free-field conditions. The frequency response, sound pressure level (SPL) and directivity are measured using exponential sine sweeps (ESS). Compared to broad band signals such as white or pink noise, the OPL can produce higher SPLs with ESS because the acoustic power concentrates on a single frequency only. This makes the OPL suitable for room acoustic measurements. A conventional dodechaedral sound source is also measured for comparison. Results show that the OPL produces a better omnidirectional sound field above $\sim 1$ kHz, but it performs worse at lower frequencies. Moreover, it presents a flatter frequency response in all directions, although it generates lower SPL values. The Directivity Index (DI) required by the ISO 3382-2 and ISO 16283-1 standards has also been computed for both sources. The OPL cannot fulfill the requirements of the standard at low frequencies. This paper also demonstrates and discusses DI measurements of high resolution both for the new OPL and the traditional onmidirectional speakers.

全向参量扬声器 (OPL) 是一种声源，由设置在球体上的数百个超声波压电换能器组成。依靠参数声学阵列 (PAA) 现象，每个换能器发射由可听信号调制的超声波载波束。由于空气中的非线性传播，自然解调发生并获得聚焦的可听波束。因此，OPL 会向各个方向发出数百个可听见的声束。在这项工作中，在自由场条件下检查了一个包含 750 个换能器的 OPL 原型，该原型设置在半径为 0.125 厘米的球体上。使用指数正弦扫描 (ESS) 测量频率响应、声压级 (SPL) 和方向性。与白噪声或粉红噪声等宽带信号相比，OPL 可以通过 ESS 产生更高的 SPL，因为声功率仅集中在单个频率上。这使得 OPL 适用于室内声学测量。还测量了传统的十二面体声源以进行比较。结果表明，OPL 产生了更好的全向声场，高于$～1$kHz，但在较低频率下表现更差。此外，尽管它产生较低的 SPL 值，但它在所有方向上呈现出更平坦的频率响应。ISO 3382-2 和 ISO 16283-1 标准要求的方向性指数 (DI) 也已针对这两个源进行计算。OPL 在低频下无法满足标准的要求。本文还演示和讨论了新 OPL 和传统单向扬声器的高分辨率 DI 测量。