Design aspects of the five string banjo

Abstract

The five string banjo is a stringed instrument that uses a drum head (membrane) to radiate sound. The strings couple to the head through a moveable bridge. Many have a removable resonator whose spacing from the main part of the banjo is adjustable to allow tuning of the internal air cavity. Holographic interferometry demonstrates vibrational modes of the head that have a strong dependence on head tension. Driving point accelerance measurements demonstrate that the ability of the bridge to be vibrated depends on the mass and stiffness of the materials used in its construction. Peak accelerances usually occur between 1800–2000 Hz. Power spectra measurements of the sound show that 99% of the sound is in a frequency range of 147–5200 Hz. Two substantial formants are seen in the power spectra. The first and largest occurs in about the 400–1800 Hz range, the same frequency range where the most substantial head modes are found. The second is from 2000–4000 Hz, a range where the series combination of bridge and head show increasing accelerances by driving point measurements. Measurements of the transient response following a pluck quantify the frequency content of the rising and falling phase.