Investigation of acoustic efficiency of wood charcoal in impedance tube for usage in sound-reflective devices

Abstract

Charcoal is an environmentally friendly, biodegradable, and economical material. This material is usually produced by slow pyrolysis—the heating of wood or other substances in the absence of oxygen. The aim of this study was to investigate the acoustic efficiency of charcoal and design an acoustic diffuser that utilizes charcoal. Samples of different types of tree charcoal—birch (Betula pendula), pine (Pinus sylvestris), and oak (Quercus robur)—with different thicknesses were used for the acoustic efficiency measurements. The sound absorption and sound reflection properties of charcoal were investigated. The bulk density of charcoal was measured. In this study, an impedance tube with two microphones was employed as the measurement method. The results of the impedance tube measurements showed that the charcoal samples had high sound reflection coefficients, the highest value of which was 1. The 50 mm samples of birch had a high bulk density of 473 kg/m3. The sample of 50 mm thick oak had the best reflection coefficient at 0.99. Reflection depended on the surface’s acoustic properties, and the sound reflection coefficient increased with the increase in the density. Charcoal measurements, due to the high reflection coefficient of the material, were used for the design of a sound diffuser, which included wooden perforated plates filled with cylindrical elements of wood charcoal.