The Resonator Banjo Resonator, part 2: What makes them really crack?

TL;DR

This study quantifies how a resonator back in a banjo amplifies high-frequency sound above 4500 Hz, revealing that the resonator's effect is more about absorption differences than direct reflection.

Contribution

It provides experimental evidence that the resonator's sound enhancement is primarily due to absorption differences, not direct reflection, clarifying the acoustic role of the resonator.

Findings

Resonator increases sound output by 6-10 dB above 4500 Hz.

No correlation between head-resonator separation and spectral response.

Absorption differences likely dominate the resonator's acoustic effect.

Abstract

A simple experiment quantifies the difference between the sound production of a banjo with and without a resonator back. Driven by a small tweeter mounted inside the pot, for frequencies above about 4500 Hz, the produced external sound is 6 to 10 dB louder with the resonator than without. With the banjo played in any normal fashion, this gives a negligible contribution to the overall volume. However, that difference is clearly a reflection of the universally recognized resonator sound, in close analogy to plosive consonants in human speech. No direct correlation is observed between the head-resonator separation and the spectrum of the enhanced response. This suggests that direct reflection off the back is not a primary contributor to the resonator/openback difference, leaving differences in overall absorption as the major suspect.