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I am aware that different surfaces can filter out or boost some harmonic frequencies of a reflected sound. But would it be possible that some surfaces could alter the fundamental frequency of reflected sound from the direct sound?

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No. I suppose it might be possible to design an exotic device which absorbed energy from the incident sound wave at one frequency and re-emitted it at a different frequency (by analogy with light phosphors, etc) but that is not the conventional meaning of "reverberation" in acoustics.

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If the interaction with the wall is linear, the dynamics of the surface can only modify the existing harmonics of the incident sound wave--it can not create new ones.

Re. 'fundamental frequency'
https://en.wikipedia.org/wiki/Fundamental_frequency

The fundamental frequency, often referred to simply as the fundamental, is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. In terms of a superposition of sinusoids, the fundamental frequency is the lowest frequency sinusoidal in the sum.

MY ANSWER: If we take the fundamental frequency to be the lowest frequency of a periodic waveform then it can not be altered by a linear interaction with the wall--except by setting its amplitude to zero. That would cause the next higher harmonic to become the new fundamental.

If the interaction is non linear then it could be altered in other ways.

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  • $\begingroup$ Speaking in terms of acoustics, what do you mean by ‘non linear interaction’? Is it something like acoustic diffuser? $\endgroup$
    – user506602
    Commented Dec 1, 2019 at 18:34
  • $\begingroup$ In terms of acoustics, it would mean something that created harmonics that did not exist before--typically higher harmonics. $\endgroup$
    – user45664
    Commented Dec 1, 2019 at 18:53
  • $\begingroup$ Thanks for the clarification. $\endgroup$
    – user506602
    Commented Dec 1, 2019 at 19:03

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