Guitar sound hole modification and its effect on tone

This paper investigates the possibility of acoustic guitar timbre modification through the use of sound hole inserts, which change the effective size of the instrument's sound hole. The multitude of different forms in which the acoustic guitar is produced and the tonal differences between them point towards a need among musicians for variety in the timbre of their instruments. A mechanism allowing for the changing of the sound produced by an existing instrument could therefore allow for flexibility and adaptability which has thus far not been possible with acoustic chordophones. One of the factors which greatly influences the acoustic guitar's tone is the characteristic of air resonances inside the instrument's resonance chamber, which are dependent on the depth and diameter of the body's opening. In this work a set of sound hole inserts is created, which after application decrease the diameter of the guitar's sound hole. Their effect on the instrument’s timbre is investigated experimentally and the achieved results are presented and discussed. Different insert diameters are also compared to investigate the more general effect sound hole diameter has on the tonal and temporal properties of an acoustic guitar.