Experimental investigation of shock wave generation in brass instruments

Acoustic shock waves are commonly associated with explosions or sonic booms from supersonic aircraft. Players of brass musical instruments are often surprised to discover that when a trumpet or trombone is played loudly the internal sound pressure inside the tubing can be sufficiently high to create a shock wave, resulting in a dramatic increase in the brightness of the timbre. The process through which the shock wave is formed, and may be subsequently extinguished by viscothermal losses before reaching the bell of the instrument, are not fully understood. This paper describes recent experiments studying the propagation of sinusoidal wave trains through model brass instruments consisting of stainless steel cylinders terminated by flaring bells. Implications for the design of brass wind instruments are discussed.