Circular Drum Head Modes: Understanding Why They Don't Always Follow the Rules

In summary, the modes of a circular drum head are described by Bessel functions and sines and cosines, but without getting into all that, it can be said that the nodes are circles concentric with the center of the drum, and are also evenly spaced lines that run through the center of the drum (i.e., diameters). However, while watching this video on youtube, the first few modes are all right, but later on at higher frequencies, the modes don't seem to meet the description above. I think it's a bonus that resonances are occurring at all, given the non-uniformities.
  • #1
RedX
970
3
The modes of a circular drum head are described by Bessel functions and sines and cosines, but without getting into all that, one can making the following statement: the nodes are circles concentric with the center of the drum, and are also evenly spaced lines that run through the center of the drum (i.e., diameters).

However, while watching this video on youtube:



the first few modes are all right, but later on at higher frequencies, the modes don't seem to meet the description above. Why is that?
 
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  • #2
RedX said:
The modes of a circular drum head
[...]
the nodes are circles concentric with the center of the drum, and are also evenly spaced lines that run through the center of the drum (i.e., diameters). [...]
However, while watching this video on youtube:


I think that if you would be able to get a material with perfectly uniform mass per unit of area, and perfectly uniform elasticity, stretched with perfectly uniform tension, then - due to the conditions being perfectly uniform - the vibrational modes will be symmetrical. In the case of the latex sheet in the video I think all of the above factors are somewhat off.

I think it's a bonus that resonances are occurring at all, given the non-uniformities.

Cleonis
 
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  • #3
RedX said:
The modes of a circular drum head are described by Bessel functions and sines and cosines, but without getting into all that, one can making the following statement: the nodes are circles concentric with the center of the drum, and are also evenly spaced lines that run through the center of the drum (i.e., diameters).

However, while watching this video on youtube:



the first few modes are all right, but later on at higher frequencies, the modes don't seem to meet the description above. Why is that?


I vote that the tension on the head is not uniform. I wonder if you can tension the head (one lug at a time) while observing the patterns, and watch the pattern move.

Also surprising to me, the nodes are so low in frequency- that explains why the sounds of a struck drum are so disperse.
 
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  • #4
There are a lot of videos on youtube that show resonance patterns in various materials. There's even a name for it: cymatics.

One of the coolest ones I've seen makes life-like forms emerge:



There seem to be entire religions/philosophies built around sound frequencies and the resonance patterns that emerge from the boundary conditions.

But they're fun to watch.
 
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1. What are circular drum head modes?

Circular drum head modes refer to the different patterns of vibration that can occur on a circular drum head when it is struck. These modes are a result of the drum head's unique shape and material properties, and can affect the sound produced by the drum.

2. Why don't circular drum head modes always follow the rules?

This is because the behavior of circular drum head modes can be affected by various factors, such as the tension and thickness of the drum head, the type of strike used, and the surrounding environment. These factors can cause the modes to deviate from the expected patterns of vibration.

3. How can understanding circular drum head modes improve drumming?

By understanding how circular drum head modes work, drummers can make informed decisions about the type of drum head and tuning that will produce the desired sound. They can also use this knowledge to troubleshoot any issues with their drum sound.

4. Are circular drum head modes important in other fields besides music?

Yes, circular drum head modes have applications in various fields such as acoustics, engineering, and physics. They can be used to study the properties of different materials, design musical instruments, and even detect defects in structures.

5. Can circular drum head modes be controlled or manipulated?

Yes, to some extent. By adjusting the tension and thickness of the drum head, and using different striking techniques, drummers can influence the behavior of the circular drum head modes. However, there will always be some level of unpredictability due to external factors.

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