A preliminary study on sound transmission characteristics of wood chips in the application of noise insulation

Abstract

Organic material in sound insulation offers additional environmental and human health benefits. This study deals with an experimental investigation of the Sound Transmission Coefficient (STC) of loosely packed wood chips for introduction as sound insulation applications. STC is calculated by measuring the Transmission Loss (TL) through wood chips between the walls of the cubical-shaped box. The material is packed securely between the walls of 5 cm thickness of a meshed cube of outer measurements 60×60×60 cm3. The sound source is placed at the center of the cube. Packing uniformity is ensured by stuffing the material evenly in known mass in a unit volume. The sound source consists of a B&K type 4292, Omni directional speaker and a type 2734 amplifier. B&K type 2250 class 1 handheld Sound Level meter is used for Sound Pressure Level measurements. SPL, inside and outside the cube, was measured for four sides, and the average value was taken. Measurements were taken in a reverberation room with 25 Hz ambient noise or less. Pink noise (12.5 Hz –20,000 Hz) in one-third of octave bands is used for the study. TL and STC were calculated, and variations were analyzed for different sound frequencies. The results imply the TL of the material is significantly dependent on the sound frequency. Sounds of frequencies less than 400 Hz are transmitted with minimum attenuation, while higher-frequency sounds significantly attenuate. These loosely packed wood chips efficiently weaken the susceptible sound frequencies (2 to 4 kHz) to the human ear. The average sound absorption coefficient in commercially available solid wood panels is much less, with a higher reflection. Because of their flexibility, the loosely packed sound insulation panels are not very attractive in the construction industry. However, loosely packed, durable organic materials could be used in the acoustic insulation industry in an creative manner, providing an esthetic appearance to the room while maintaining good health.