Interpretation of a signal (sound) spectrum - hydrophones

AI Thread Summary
The discussion focuses on the interpretation of a sound spectrum from hydrophones, specifically noting that the fundamental frequency is approximately 40 kHz. There is uncertainty regarding a large 210 kHz signal, which may be an alias, and the presence of second and third harmonics is acknowledged without clear causation. The original poster mentions that the paper suggests these harmonics result from non-linear effects in the liquid, but they express a need to verify if the driver might be responsible instead. The poster has resolved their initial confusion but continues to seek clarification on the harmonics. Overall, the thread highlights the complexities of analyzing sound spectra in hydrophone studies.
rwooduk
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ooops so obvious sorry! please delete
 
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The 40kHz is from the axis. The fundamental appears at about 0.4 on the scale, which is per 105 Hz, so that is 0.4 x 105 Hz, or 40 kHz.
As for the rest, it's not at all clear to me. They don't seem to mention the large 210 kHz signal which is the same size as the fundamental. Maybe this is an alias? The symmetry makes me think this.
The second and third harmonics appear in b,c & d, but as to what causes them there's no indication.
Edit: I haven't read the paper, though they appear to be claiming the harmonics are due to non-linear effects in the liquid. I would want to check carefully that it's not non-linear effects in the driver.
 
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Thanks for the reply, i just figured it out as i posted and can't delete the thread. Thank you though!
 

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