The loss of energy due to the absorption of sound is inversely proportional to the sound intensity. Diffusion is a result of friction caused by the interpenetration of moving particles or molecules between two different gasses, liquids, or solids. Under certain conditions, some of the particles in a sound wave may travel with the wave, which can lead to the absorption of sound caused by diffusion. A portion of the energy or momentum in a sound wave which travels from a warm region of a medium to a cooler region is absorbed into the surrounding medium. Heat conduction is caused by friction due to variations in temperature in different regions of a medium. Viscosity is the occurrence of molecular friction between two different regions of a gas or liquid that flow parallel to one another at different speeds or temperatures. The transfer of sound energy into heat energy is caused by an increase in the frequency of vibration and greater density of particles, due to the transmission of sound through the comparatively narrow passages in the medium, or by viscosity or heat conduction. The absorption loss in a sound wave is the energy that is converted into heat by friction, which occurs during the energy transfer process from a region of lesser density to a region or medium of greater density, or from a region of warmer to cooler temperature. The absorption loss rate of a sound wave varies with density and temperature, and increases with frequency. The absorption of sound is an energy transfer process in which sound energy is converted into heat. The absorption of sound is the process by which sound energy is diminished in passing through a medium to another medium of greater density, or through regions of greater density or lower temperature of the same medium. The shape of an absorbed wave is defined by the geometrical dimensions of the obstruction through which the wave passes. The frequency and velocity of an absorbed wave is increased, and the amplitude and intensity of the wave is decreased, due to the increased density of the obstruction. The shape of a deflected sound wave varies with the different modes of deflection, and depends upon the dimensions of the obstruction, and the wavelength of the sound.Ī portion of a sound wave which encounters an obstruction is absorbed and transmitted through the obstruction along a path normal to the direction of propagation, and the degree of absorption depends on the various characteristics of the obstruction and the mode of deflection. Normally, the frequency and amplitude of a deflected wave remains the same as that produced by the original wave. When a sound wave travels through regions of a medium which vary in temperature, pressure, or density, the sound is refracted in the direction of the region of incidence.Īn obstruction in the path of sound acts as a sound source which changes the direction of the original wave, and may cause a change in the frequency, amplitude, or intensity of the wave, usually by an amount which is imperceptible to the human ear. If the dimensions of an obstacle are nearly the same as the wavelength of the sound, sound interference may occur. If the dimensions of an obstacle are small compared to the wavelength, the sound is diffracted in various directions depending on the characteristics of the obstacle. If the dimensions of an obstacle are large compared to the wavelength of the sound, the sound wave is reflected or scattered by the obstacle in the direction of the region of incidence, with some of the sound being absorbed, depending on the degree of elasticity of the obstacle.
The deflection of sound refers to sound waves which are reflected, scattered, diffracted, or refracted by an obstruction, and depends upon the dimensions, substance, and density of the obstruction, and the wavelength of the sound. Sound waves which strike an obstacle or encounter a region of a medium of different temperature, pressure, or density are deflected, absorbed, and transmitted through the obstacle or region of the medium. The obstruction of sound occurs when a sound wave travels through a medium to another medium of greater density, such as an obstacle which is positioned directly in the path of sound, or through different regions of temperature, pressure, or density of the same medium.