ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5aEA6. Active noise control for attenuation of low-frequency broadband jet engine exhaust noise.

Jerome P. Smith

Ricardo A. Burdisso

Chris R. Fuller

Vib. and Acoust. Labs., Dept. of Mech. Eng., Virginia Polytech. Inst. and State Univ., Blacksburg, VA 24061-0238

Rob Gibson

WYLE Labs., Arlington, VA 22202

Low-frequency broadband jet engine exhaust noise radiated into the surrounding area has been a problem for facilities that perform ground jet engine run up operations such as military hush-houses. This low-frequency acoustic radiation is capable of propagating over long distances, creating a noise and vibration problem in nearby communities. In this paper, active noise control (ANC) is experimentally implemented to achieve attenuation of low-frequency turbo-fan jet engine exhaust noise in a nearby area. The control method is the feedforward filtered-x LMS algorithm and is implemented for both single-input, single-output and multiple-input, multiple-output systems. The control inputs are generated by filtering a reference signal through adaptive FIR filters before being input to the control loudspeakers, and microphones are used to generate the reference and error signals. Attenuations of up to 15 dB are achieved in the 1/3-octave bands at the error sensor locations. The results also demonstrate a large area of reduction surrounding the error microphones with overall attenuations of up to 7 dB and generally agree with analytical predictions. Results are demonstrated for both a running jet engine in a small scale hush-house facility and an unsuppressed running jet engine. [Work sponsored by the U. S. Air Force.]