Helmholtz for a dummy

Scarrafone effec

Some result.
In measurements without diffusers, a hum appears. A fan? The refrigetor?


Edit: Scarrafone, cockroach. From an italian expression ""Ogne scarrafone è`bello a mamma soia", every cockroach looks beatiful to his mom.
 

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any formula to calculate the resonance Freq vs pipe diameter & length? i also have this idea using pvc pipe and it also looks fun for my boys
 

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nice experiment Bicicletta!
guys do you have any idea why the very same cavity with a hole (+neck) acts as a resonator in some context (e.g. blowing across the neck of a bottle, enhancing the sound of a guitar body, allowing for the bass reflex effect in a loudspeaker cabinet) and as a selective noise filter in others (e.g. bass traps, acoustic panels, attenuation elements in engine intake systems) even when the cavity is not filled with absorption material?
how come the same element can act in two opposite ways? any clue?