Alleged use of LRAD (Long Range Acoustic Device) at G20 protests in Pittsburgh, Pennsylvania.
Pittsburgh Police Department Warning (transcript):
By order of the City of Pittsburgh Chief Police:
I Hereby Declare This to Be an Unlawful Assembly.
I order all those assembled to immediately disperse.
You must leave the immediate vicinity.
If you remain in the immediate vicinity,
you will be in violation of the Pennsylvania Crime Code …
no matter what your purpose is.
At maximum level, LRAD 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.
Countermeasures may include the use of passive hearing protection (earplugs, headsets), which may bring the sound down to ineffective levels. In addition, sound could be reflected from a solid surface, and redirected back to the originator.
Pittsburgh Police use LRAD Sonic Weapon on Liberty Avenue.