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LRAD: Long Range Acoustic Device บางส่วนจาก Wikipedia ครับ
The Long Range Acoustic Device (LRAD) is a crowd-control and hailing device developed by American Technology Corporation.
According to the manufacturer's specifications, the equipment weighs 45 pounds (20 kg) and can emit sound in a 30° beam (only at high frequency, 2.5 kHz) from a device 83 centimetres (33 in) in diameter. At maximum level, it can emit a warning tone that is 146 dBSPL (1,000 W/m²) at 1 metre, a level that is capable of permanently damaging hearing, and higher than the normal human threshold of pain (120–140 dB). The maximum usable design range extends to 300 metres. At 300 metres, the warning tone (measured) is less than 90 dB. The warning tone is a high-pitched shrill tone similar to that of a smoke detector.
There appears to be some disagreement over these specifications, as some[who?] have reported measurements that differ from the manufacturer's specifications, and show reduced output with a less directive beam.
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http://en.wikipedia.org/wiki/Long_Range_Acoustic_Devicehttp://www.atcsd.com/site/content/view/15/110/
