Study on the source of overtone series in a harmonica note

The harmonica reed is a cantilever beam and therefore does not produce integer harmonics. High-speed camera video of the reed and vibrometer measurements both demonstrate this expected behavior at the reed tip when being played. However, the acoustical recording shows an integer overtone series with large amplitudes (<10 dB from the fundamental) all the way past 22 kHz. To understand this phenomenon, we eliminated resonant cavities and other possible acoustic feedback systems by plucking the reed with only the reed plate attached. The acoustical and vibrometer data showed the same discrepancy in this case, but only when the reed enters the reed slot in the reed plate. The overtones don’t show up when the reed is vibrating completely away from the reed slot. In this paper, we will present these data and show how this phenomenon could be a result of vorticity produced by the sharp edge of the plate and the small air layer gap between plate and reed.