# Interpretation of a signal (sound) spectrum - hydrophones

• rwooduk
In summary, The conversation discusses frequencies and harmonics in a liquid and their possible causes. The main focus is on a 40kHz frequency and its relationship to the large 210 kHz signal and the appearance of second and third harmonics. The cause of these harmonics is not mentioned, but the paper suggests they may be due to non-linear effects in the liquid or the driver.
rwooduk
ooops so obvious sorry! please delete

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.

rwooduk
Thanks for the reply, i just figured it out as i posted and can't delete the thread. Thank you though!

## 1. What is a hydrophone?

A hydrophone is a type of microphone designed to capture and interpret sound waves underwater. It is commonly used in marine research, oil and gas exploration, and underwater communication systems.

## 2. How does a hydrophone work?

A hydrophone works by converting sound waves into electrical signals. It consists of a piezoelectric element that converts pressure variations caused by sound waves into electrical voltage, which is then amplified and interpreted by a computer or other signal processing equipment.

## 3. What is a sound spectrum?

A sound spectrum is a visual representation of the different frequencies and amplitudes present in a sound wave. It is often depicted as a graph with frequency on the horizontal axis and amplitude on the vertical axis.

## 4. How can a hydrophone be used to interpret a sound spectrum?

A hydrophone can be used to capture underwater sound waves and convert them into a sound spectrum. By analyzing the different frequencies and amplitudes present in the spectrum, scientists can identify and interpret the source of the sound, such as marine animals or man-made structures.

## 5. What are some challenges in interpreting a sound spectrum from a hydrophone?

Some challenges in interpreting a sound spectrum from a hydrophone include background noise, variations in sound wave propagation, and the need for advanced signal processing techniques. Additionally, the interpretation of a sound spectrum may also be influenced by factors such as water temperature, salinity, and depth.

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