Air vibrating in a cylindrical cavity

AI Thread Summary
The discussion centers on the sound produced by air passing over a cylindrical cavity, specifically a brass column with a hole. The key question is whether the sound behaves like a Helmholtz resonator or a closed-ended resonant air column, and which equations can determine the frequency. The analogy of blowing across a straw illustrates the principles at play, highlighting how the pitch is influenced by the length of the straw and the velocity of the air blown. A longer straw results in a lower fundamental frequency, while increased blowing intensity raises the pitch. Understanding these dynamics is essential for accurately predicting the sound characteristics in this setup.
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The diagram accompanying this post shows a cylindrical column bored at right angles to a flat surface. Let’s say the material is a block of brass with a hole drilled in it. The arrow represents a fast moving stream of compressed air. As the air passes over the top of the column a high pitched sound is generated. The question is what determines the pitch of the sound produced, is it behaving like a Halmholtz resonator or is it behaving like a closed ended resonant air column, what equation can be used to accurately determine the frequency produced?

Consideration:
Take a drinking straw and insert it into a glass of water. Now blow across the top open end of the straw and the water will rise up the straw. The harder you blow the grater the vacuum generated thus the higher the water rises (venture effect).
The venture effect in the above set-up generates a vibrating vacuum which is responsible for the sound generated.
 

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depends on what you mean by pitch

If you are talking about the frequency it would be limited by the length of the straw. A longer straw would have a lower fundamental frequency and the level of the octave would be based on the velocity of blow a harder blow would initiate a higher octave
 
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