Читать книгу Engineering Acoustics - Malcolm J. Crocker - Страница 139

When the wavelength of sound is large compared to physical dimensions of the acoustical system under consideration, then the lumped‐element approach is useful. In this approach it is assumed that the fluid mass, stiffness, and dissipation distributions can be “lumped” together to act at a point, significantly simplifying the analysis of the problem. The most common example of this approach is its use with the well‐known Helmholtz resonator (see Chapter 9 of this book) in which the mass of air in the neck of the resonator vibrates at its natural frequency against the stiffness of its volume.

A similar approach can be used in the design of loudspeaker enclosures and the concentric resonators in automobile mufflers in which the mass of the gas in the resonator louvers (orifices) vibrates against the stiffness of the resonator (which may not necessarily be regarded completely as a lumped element). Dissipation in the resonator louvers may also be taken into account. Chapter 21 in the Handbook of Acoustics [1] reviews the lumped‐element approach in some detail.