Air column effects and direct radiation due to bell vibrations of a brass wind instrument
Thomas R. Moore; Daniel W. Zietlow; Wilfried Kausel

The effects of wall vibrations on the sound of modern brass instruments has been a topic of discussion for decades. Recent theoretical work has indicated that damping the breathing modes of the flaring bell may be responsible for observed changes in the sound when wall vibrations are damped. We present measurements of the changes in the transmission function, input impedance, and acoustical signature of a modern trumpet when vibrations of the bell are heavily damped, and compare them to predictions from such a theory. The magnitude of the effect attributable to changing the air column is compared to the effect attributable to direct radiation of the vibrating bell. Measurements indicate that much, but not all, of the change in the sound of a brass wind instrument that results from damping bell vibrations can be attributed to changes in the air column. The magnitude of these changes compares well with the theory.