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The Long Range Acoustic Device (LRAD) is an acoustic hailing device developed by LRAD Corporation to send messages and warning tones over longer distances or at higher volume than normal loudspeakers. LRAD systems are used for long range communications in a variety of applications〔Applications - LRAD Corporation website ()〕including as a means of non-lethal, non-kinetic crowd control. Though they have been called "sonic weapons", LRADs are not inherently for military use. According to the manufacturer's specifications, the systems weigh from and can emit sound in a 30°- 60° beam at 2.5 kHz.The manufacturer also produces systems for public address and mass notification use that broadcast 360°.〔LRAD Corporation website ()〕 LRAD systems are used by maritime, law enforcement, military and commercial security companies to send instructions and warnings over distance, and can be used to initiate. LRAD systems are also used to deter wildlife from airport runways, wind and solar farms, nuclear power facilities, gas and oil platforms, mining and agricultural operations, and industrial plants. ==Function== The parameter "ka", which is the wave number multiplied by the speaker radius, is often used to characterize sound source directivity. For this source, ka=19 at 2.5 kHz, and according to the LRAD data sheet, the beam angle of about 30 degrees total is precisely what is predicted for a regular loudspeaker.〔Beranek, Leo L. 1986. Acoustics, p.132, American Institute of Physics.〕 Small spherical "point-source" acoustic devices follow the known inverse square law, which predicts the loss of 6 dB per doubling of distance from the source, solely due to geometric spreading. Large speakers (or large arrays), such as these, have an interference pattern in the nearfield which produces peaks 6 dB higher than the output pressure and nulls where the pressure is essentially zero.〔Blackstock, David T. 2000. Fundamentals of Physical Acoustics, p.456, John Wiley and Sons.〕 The larger the speaker, and the higher the frequency, the longer the effective nearfield. The nearfield for this device is approximately 8m.〔 LRAD Corporation was formerly named American Technology Corporation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「long range acoustic device」の詳細全文を読む スポンサード リンク
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