Cupping a hand over the ear boosts hearing via Helmholtz resonance

Evidence

Holding a cupped hand over an ear is a familiar sight, often used as an aid to hearing, even by people with excellent hearing. Why does it work? There may be some reflection of high-frequency sound, but mainly the cupped hand creates a variable-frequency Helmholtz resonator (depending on how large the opening is, and the volume enclosed by the hand and head), which enhances sound in the vicinity of the resonance frequency. In a noisy environment, remarkable changes are apparent when the hand is adjusted to form Helmholtz resonators with various resonance frequencies. Usually, the opening formed by the hand is quite big, causing the resonance to appear at relatively high frequency. Try varying the opening of a cupped hand all the way down to closed. Ambient noise typically provides a broadband source; the enhanced frequency band becomes clearly apparent as it changes pitch with position of the hand. The effect is rather like “listening” to a seashell, which is itself a resonant cavity. — Eric J. Heller, Why You Hear What You Hear- An…, 1213

Categorization

• SEED: The cupped-hand-as-tunable-hearing-aid is a vivid why-do-we-hear-what-we-hear example linking body facts to resonance physics.
• QUESTION: Could tuning the cupped-hand resonator be intentionally used in hearing-restoration contexts, or is its band too narrow to help speech?