Interpretation of a signal (sound) spectrum - hydrophones

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SUMMARY

The discussion centers on the interpretation of a sound spectrum obtained from hydrophones, specifically analyzing a fundamental frequency at 40 kHz and a significant 210 kHz signal that may represent an alias. The second and third harmonics are noted in sections b, c, and d, with speculation that they arise from non-linear effects in the liquid, although the possibility of non-linear effects in the driver is also suggested. The user acknowledges a lack of clarity in the original paper regarding the causes of these harmonics.

PREREQUISITES
  • Understanding of sound spectrum analysis
  • Familiarity with hydrophone technology
  • Knowledge of harmonic frequencies and aliasing
  • Basic principles of non-linear dynamics in fluids
NEXT STEPS
  • Research the principles of sound spectrum analysis in hydrophones
  • Explore the concept of aliasing in signal processing
  • Study non-linear effects in fluid dynamics
  • Review literature on harmonic generation in acoustic signals
USEFUL FOR

Acoustic engineers, researchers in fluid dynamics, and anyone involved in sound analysis using hydrophones will benefit from this discussion.

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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