Finding the air cavity resonance of a propane tank for a drum.

[great_sushi]

I am going to build a drum out of a propane tank. I think it will be handy to find the resonant frequency of the tank and choose the tuning accordingly so not to pick frequencies that are extremely damped.

I have a cavity resonance formula found on hyper physics

I am not going to build a drum with only one note, there will be approximately 7. 7 notes in most scales. http://muzmaker.ru/uploads/posts/2009-04/1240604374_717ff323216270166.jpg
If you look at the image you'll see the notes, I am going to refer to them as tongues.

Once I find the resonant frequency I can decide on the tuning. Another problem is choosing the dimensions of the tongues at the top. I've been trying to find another formula so that I can determine the size of the tongues, so a larger tongue results in a slower oscillation producing a lower note and vice versa. But I will need to relate the tongue dimensions to the resonant frequency of the tank.

Im curious to know how to calculate the resonant frequency of something steel with particular dimensions.

Once I have that relation I can move forward. Also, fine tuning will be done by either bending the tongue downward/upward permanently as to result in a lower/higher frequency respectively.

Thankyou, If all goes well, my drummer sister will have another present for christmas.

 

[NascentOxygen]

Do you have an oscilloscope on which to measure frequency, if you were to use a microphone? (You might also need an amplifier.) If you held a microphone at the mouth of the cavity, and dropped a marble inside, you'd record a decaying echo which would be the frequency of resonance. I don't quite understand how something like this could simultaneously have 7 unrelated resonant frequencies, but maybe that is possible. I don't claim to understand much about the mysteries of music.

 

[great_sushi]

I don't have a microphone but I could introduce a speaker into the cavity and do a frequency sweep. Noting the frequencies that 'stand out'. I imagine that there will be one natural frequency and perhaps 'n' integer values of the wavelength.
Say having one wave with (i think its nodes where you hear maximum intensity) nodes at both ends, (only two). Then one whole wavelength with 3 nodes, then 4 nodes, then 5.
I might not be explaining it very well and I may be wrong.

It would be great if someone could explain it properly

 

[NascentOxygen]

On further reflection, I guess the air cavity could have a resonant frequency that is independent of the mechanical resonance of the steel shell. I expect drumming effect would be most impressive when the design sees these two frequencies coincide.

You certainly could try sweeping the speaker frequency and listening for a peak, but when I tried this using a column of glass tube as a class demo, the peak was as good as imperceptible.

An idea that could hold promise involves introducing both a microphone and a speaker into the cavity, the speaker delivering an amplified version of what the mic picks up. As the gain is turned up, feedback should see the system begin to oscillate and show feedback squeal. I expect that frequency of oscillation would be the resonant frequency of the cavity. You might be able to press into service the mic and earpiece from a discarded cell phone for this. This isn't going to reveal multiple resonant frequencies, though.

 

[PJC01]

I find your project to be both interesting and challenging. Finding the resonant frequency of a propane tank for a drum is not a straightforward task, but with the right approach, it can be achieved.

First, I would suggest conducting some preliminary experiments to determine the natural frequency of the propane tank. This can be done by tapping the tank at different points and recording the sound produced. By analyzing the sound waves, you can identify the natural frequency of the tank.

Next, I would recommend using the cavity resonance formula found on hyper physics to calculate the resonant frequency of the tank. This formula takes into account the dimensions and material of the tank, and can give you a good estimate of the resonant frequency.

When it comes to choosing the tuning for your drum, I would suggest using the natural frequency of the tank as a starting point. This will ensure that the drum produces clear and undamped tones. From there, you can fine-tune the tuning by adjusting the size and shape of the tongues on top of the tank.

To determine the dimensions of the tongues, I would recommend using the formula for calculating the length of a vibrating string or rod, which takes into account the material, tension, and density of the object. This can help you relate the tongue dimensions to the resonant frequency of the tank.

Lastly, as you mentioned, fine-tuning can be done by bending the tongues either downward or upward to produce lower or higher frequencies respectively. This is a common technique used in instrument-making and can be effective in achieving the desired tuning.

Overall, your project requires a combination of experimentation and mathematical calculations. I suggest consulting with experts in the field of acoustics and instrument-making for further guidance and assistance. Good luck with your project, and I hope your sister enjoys her unique Christmas present!