The diatonic harmonica, pipe resonators, and the siren Free

A number of measurements of reed motion and sound field have been made on a diatonic harmonica mounted on a fixed volume wind chamber. These include variation of sounding frequency with blowing pressure and the degree to which the sounding frequency and sound spectrum can be altered by attaching external pipe resonators. Differences were observed between the behavior of blow and draw reeds as well as the dependence of the results on whether the secondary reed in the reed chamber is allowed to vibrate. As noted by Helmholtz, at a simple level of analysis, the sound production of a free reed is similar to that of a siren, in both cases involving an air stream that is periodically interrupted. Our current results are compared with the results of measurements made in an earlier study of a siren in similar experimental configurations. [Work partially supported by National Science Foundation REU Grant PHY-1004860.]