Experimental investigation of air-driven free reeds using a laser vibrometer system

Previously reported measurements of free-reed vibration using a variable impedance transducer (VIT) gave a picture of the motion of a point on the reed throughout its cycle [J. P. Cottingham, J. Acoust. Soc. Am. 105, 940 (1999)]. A more detailed picture of the reed motion throughout its vibrational cycle has been obtained by measuring reed velocity using a laser vibrometer system. Unlike the VIT sensor, the laser vibrometer can be scanned along the reed, allowing reed profiles to be obtained. The laser system is also usable on reeds of magnetic material (e.g., steel accordion reeds) as well as reeds too small and inaccessible for the VIT. In this investigation the emphasis has been on comparison of the vibrational motion of accordion reeds with that of the reed organ reeds which had been measured in earlier studies. Some of the differences observed between the two types of reeds can be related to the structure of the reed tongues and frames.