Helmholtz Resonance Explained

To better understand Helmholtz resonance, think about the deep tone you make when you blow across the neck of an empty bottle. The air pressure created by your mouth presses the air column in the bottleneck downward, thereby increasing the elasticity of the enclosed air.

The air column will be pressed up through the bottleneck and then pressed down again by the air pressure from your mouth. In this way, the air column vibrates and a low-frequency tone is generated.

Helmholtz Resonance in Hearing Aids

The resonance works in much the same way with hearing aids as it does in a bottle.

The earmould’s vent connects the ear cavity with the atmosphere outside the earmould. The earmould and ear canal therefore function as a Helmholtz resonator, providing a small degree of amplification of the sound in the ear canal at a certain frequency.

The resonance frequency is at around 500 Hz, depending on the size of the vent in the earmould.

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