Air modes of the Bacon internal resonator banjo

TL;DR

This study investigates the air resonant modes of the Bacon internal resonator banjo by measuring sound in various configurations, confirming a simple model of air modes that aligns with player observations.

Contribution

It provides a detailed analysis of the air modes in the banjo's body, decoupling them from the soundboard to validate a simple theoretical picture.

Findings

Air modes are consistent across similar constructions.

Decoupling the head confirms the robustness of air mode features.

Results align with qualitative player distinctions.

Abstract

Sound measurements on a sequence of related, similar constructions with slightly different dimensions confirm a simple picture of the air modes of the internal resonator banjo's body. For the purpose of this study, the air modes are decoupled from the soundboard (i.e., [drum] head) modes by replacing the head with 3/4" plywood. The resulting characteristic features survive the strong coupling of the air modes to the head and are in accord with the qualitative distinctions recognized by banjo players.