Development of a high-directivity speaker system for improving sound environment

用于音频应用的参数阵列的实际开发最近取得了进展。实际上，大多数说话者都是指向性的。然而，参数扬声器具有明显的方向性。高指向性音响系统具有像聚光灯一样狭窄的音频波束，可以将声音传输到相邻位置的人无法检测到的特定区域。本研究开发了一些新技术，如适当的信号处理，以改善谐波失真，并应用于有声交通信号，为直过马路提供可靠的指导。从扬声器的发射器调制载波超声的一种实用方法是利用音频信号（如语音）的包络来减少扬声器工作时的电力消耗。首先，我们用数字信号处理器制造了一个包络调制器，并明确了扬声器在工作中的功耗比传统调幅降低了36%。二是着力提高电能到声能的转换效率。通过在超声发射器的输入端并联适当的线圈，可以减小发射器的无功电流，合理地提高功率效率。对于语音和音乐节目，通过连接线圈，平均电力实际上减少了约30%。此外，讨论了采用包络载波调制SSB的前景方法，以降低参数声的失真。使用具有清晰指向性的参数扬声器发出的可听交通信号比传统扬声器发出的交通信号在人行横道上更容易定位。最后，通过参数化扬声器的使用，实验证明视障行人可以在较少离开人行横道的情况下完成过马路，为直接过马路提供了可靠的指导。

Practical development of a parametric array for audio applications has been advanced recently. Actually, most speakers are directional. However, the parametric speaker is directional remarkably. High directivity sound systems having narrow audio beams like a spotlight can transmit a sound to a specific area that cannot be detected by people in adjacent locations. Some new technologies such as appropriate signal processing to improve harmonic distortion are developed in the present research project with an application to an audible traffic signal which provides reliable guidance for going straight across the street. A practical modulation of the carrier ultrasound from an emitter of the speaker is to use the envelope of audio signals such as speech to reduce electric power consumption in working the speaker. First, we have fabricated an envelope modulator with a digital signal processor and made clear that the speaker in working consumes less power with 36% reduction compared with a conventional amplitude modulation. Second, we have focused on improvement of the conversion efficiency from electric power to acoustic power. By connecting an appropriate coil in parallel with the input terminals of the ultrasonic emitter, we were able to reduce reactive current in the emitter, improving the power efficiency reasonably. For speech and music programs, the average electric power was actually reduced by about 30% by connecting the coil. Moreover, the prospective modulation method of SSB with an envelope carrier is discussed to reduce distortion in parametric sounds. Using audible traffic signals emitted from a parametric speaker with sharp directivity are more localizable in a crosswalk than those from a conventional speaker. Last, the use of the parametric speaker has experimentally demonstrated that visually impaired pedestrians can complete the crossing with less getting out of the crosswalk, providing reliable guidance for going straight across the street.