Influence of Wood and Thickness of Back Wall of Wooden Organ Pipe and Air Pressure in Windchest on Sound

Abstract

In the past, organ builders used many tree species for the production of wooden organ pipes, and the thicknesses of the pipe walls were also different. From the point of view of the sound of wooden organ pipes, it appears that the type of wood, as well as the thickness of the pipe wall, affect the resulting organ sound. Therefore, this research focused on how the wood species and the thickness of the pipe’s wall affect the sound of the organ. Two wood species were selected for our experiment: maple wood, representing hardwood; and spruce wood, representing softwood. The physical and acoustic characteristics (PACHs)—density (ρ), dynamic modulus of elasticity along the wood grain (EL), specific modulus (Esp), speed of sound along the grain (cL), resonant frequency (fr), acoustic constant (A), logarithmic decrement (ϑ), loss coefficient (η), acoustic conversion efficiency (ACE) and sound quality factor (Q)—were determined. Subsequently, the boards were used for making the back wall of the experimental wooden organ pipe with a replaceable back wall. The boards used for the back wall had an initial thickness of 7 mm. The boards were gradually thinned in 1 mm decrements to a final thickness of 1 mm. For each board thickness, the frequency spectrum was recorded at four different air pressures in the windchest, namely, 588 Pa, 716 Pa, 814 Pa and 941 Pa. The results of the experiment showed that at a given back wall thickness, the fundamental tone frequency increases with increasing air pressure. The decrease in the back wall thickness was manifested by a decrease in the fundamental frequency. With increasing air pressure, the intensity of higher harmonic frequencies also increased.