It's pointed out in the passage that the new acoustic systems developed for the US military

The US company, "Scientific Applications and
Research Associates" (SARA) Inc, has developed
crowd-dispersal weapons for the US military that
generate high-intensity sound waves. Sound levels of
120 to 130 decibels cause pain and blurred vision;
above 140 decibels, sound produces profound
discomfort throughout the body. Ear plugs are no
protection. These acoustic systems have a directed
beam, projecting the sound in a narrow fan. They
include high-intensity sound generators with power
levels of up to 60 kilowatts and are combustion
driven, using a series of small explosions to create a
noise or drive a siren or whistle.