How does the frequency of a diaphragm vary?

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In summary, the frequency of the vibration in an air horn is determined by the mass and stiffness of the diaphragm, as well as the pressure of the air and the dimensions of the horn itself. To produce ultrasonic frequencies, it is best to use a small diaphragm, a small opening, and stiff materials.
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walshlg
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I've been looking at "how to" vids that show how an air horn works: basically a thin diaphragm of metal, or even balloon rubber, is made to vibrate by passing compressed air over its surface.

Can anyone tell me how you control the frequency of the vibration to control the tone produced. Q:
1 ) From the spring equation I guess that the frequency is proportional to sqrt(1/mass), does that sound right?
2) How does this vary with the diameter of the disk?
3) Any other tips on dimensions and clearances? I'd like to get just ultrasonic, eg. 30KHz.

P.S. yes, I see that there are lots of vibration modes but I'm looking for the strongest, I assume its (1,0)
 
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1) The frequency of the vibration is determined by a combination of the mass of the diaphragm and the stiffness of the spring that holds it in place. The equation you mentioned is correct, though it only applies to the resonance frequency (i.e. the frequency at which the diaphragm vibrates most strongly). The actual frequency that is produced will depend on the pressure of the air passing over the diaphragm, as well as the dimensions of the horn itself (see below). 2) The diameter of the disk does affect the frequency of the vibration, but not in a linear way. The larger the disk, the lower the frequency. 3) To make an air horn that produces ultrasonic frequencies, the best tip is to reduce the size of the diaphragm as much as possible. This will increase the frequency of the vibration. You also want to ensure that the horn has a small opening, as this will increase the air pressure which will further increase the frequency. Finally, you should make sure that the spring and the diaphragm are as stiff as possible, as this will allow the diaphragm to vibrate more quickly.
 

FAQ: How does the frequency of a diaphragm vary?

1. How does the frequency of a diaphragm change with different materials?

The frequency of a diaphragm can vary depending on the material it is made of. Generally, stiffer materials have a higher natural frequency, while more flexible materials have a lower natural frequency.

2. Does the size of a diaphragm affect its frequency?

Yes, the size of a diaphragm can impact its frequency. Generally, larger diaphragms have a lower natural frequency, while smaller diaphragms have a higher natural frequency.

3. How does the tension of a diaphragm impact its frequency?

The tension of a diaphragm can affect its frequency. A tighter diaphragm will have a higher natural frequency, while a looser diaphragm will have a lower natural frequency.

4. Can the shape of a diaphragm affect its frequency?

Yes, the shape of a diaphragm can impact its frequency. Different shapes can lead to different modes of vibration, resulting in different natural frequencies.

5. Does the thickness of a diaphragm play a role in its frequency?

Yes, the thickness of a diaphragm can affect its frequency. Thicker diaphragms tend to have a lower natural frequency, while thinner diaphragms have a higher natural frequency.

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