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Doppler shifts in loudspeaker. Fact or fiction?

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The document below presents a brief analysis of wave form distortion in loudspeaker dynamic drivers when reproducing both a single tone as well as 2 arbitrary tones such that the different frequencies are related as Fh = n Fl, where n is any number greater than 1.0. The single tone analysis shows that when a driver subjest to a single sine wave input, the acoustic output will under go a distortion of the wave form. The level of this distortion is dependent on the driver displacement. In the two tone case, it is shown that in addition to the wave form distortion present for a single tone, there is also a frequency shift in the higher frequency. The amount of frequency shift is primarily dependent on the excursion of the driver associated with the lower of the 2 frequencies, and completely independent of the excursion related to the higher frequency. If the frequency shift is give by df, then it is shown that the higher frequency tone oscillates about the input frequency Fh as F = Fh +df sin(2*Pi*Fl*T). It is also shown that the magnitude of df asymptotes to a limiting value as the ratio of the frequencies, n, gets large. The frequency shift is shown to result in the creation of intermodulation sidebands, thus rsulting in IM distortion of the input signal. The document is in MS Word format, is about 230K and downloads quickly. Download Document, Wave Form Distortion in Loudspeaker Dynamic Drivers. On the next page I present experimental data supporting the results predicted by the analysis.  If you have any comments or questions regarding the analysis please e-mail me or post you question to the Madisound disscussion group. John k...