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An antinoise generator, a device designed to reduce the sound of buses, is being tested in New York, Houston, Texas and two transit systems in Southern California. A computer-driven 220-watt speaker, invented by Noise Cancellation Technologies Inc., Stamford, Connecticut, is placed in the tailpipe of the vehicle and emits sound waves to partially cancel exhaust noise. But the New York Times reports the electronic muffler is of greater interest to transit officials for its fuel efficiency traits: the technology makes it easier for the bus to emit exhaust which in turn raises horsepower and increases fuel economy Further muffling technology may eventually be able to quiet transmissions, drivetrains and fans or air-conditioning compressors.