- #1

Squizzie

- 148

- 9

- TL;DR Summary
- Looking for a physics text on sound or wave theory, explaining the circumstances where frequency and wavelength are not linearly proportional.

I have come across the term "nonlinear acoustics" in various technical reports and engineering texts, but have been unable to nail it down in a modern physics textbook.

It appears to relate to the transmission of pressure waves in which either the frequency and wavelength are not linearly dependent, or where the speed of the wave is dependent on the amplitude of the wave, i.e. the pressure.

I thought I had found it in Feynman, with:

"

but was disappointed that the closest Chapter 48 came was the tantalising:

"

I was unable to find a description of any case where where ω and k are not linearly proportional.

I know in BLAST WAVE Chapter 5, Hans Bethe proposed a "

As Feynman pointed out: "

As mentioned, I have found references in journal articles, Wikipedia and some engineering texts, but can't find it in any mainstream physics textbooks. As this is a physics forum, I wonder if members can assist.

It appears to relate to the transmission of pressure waves in which either the frequency and wavelength are not linearly dependent, or where the speed of the wave is dependent on the amplitude of the wave, i.e. the pressure.

I thought I had found it in Feynman, with:

"

*Both sound and light travel with a speed in air which is*" (my emphasis),**very nearly**independent of frequency. Examples of wave propagation for which this independence is not true will be considered in Chapter 48.but was disappointed that the closest Chapter 48 came was the tantalising:

"

*Incidentally, we know that even when ω and k are not linearly proportional, the ratio ω/k is certainly the speed of propagation for the particular frequency and wave number.*"I was unable to find a description of any case where where ω and k are not linearly proportional.

I know in BLAST WAVE Chapter 5, Hans Bethe proposed a "

*theory to provide a natural transition to the well-known acoustic theory, and to set in evidence the limitations of the latter*." (referred elsewhere in the paper as the "semi-acoustic theory") and went on to develop a theory that was implemented in the "IBM runs" of that paper, but I am unable to find any evidence that it made its way into mainstream physics in the intervening 70-odd years.As Feynman pointed out: "

*The principle of science, the definition, almost, is the following: The test of all knowledge is experiment. Experiment is the sole judge of scientific "truth.*". I am concerned that there does not appear to be any experimental evidence for the existence of acoustic waves in which frequency and wavelength are not linearly dependent.As mentioned, I have found references in journal articles, Wikipedia and some engineering texts, but can't find it in any mainstream physics textbooks. As this is a physics forum, I wonder if members can assist.

Last edited: