Category: 3. Sound Generation and Propagation

Again in the case of the oscillating piston, we will consider the sound power radiated by the piston into the tube. The sound power radiated by the piston, W, is (3.18) But from Eqs. (3.10) and (3.14) the power is (3.19) and close to the piston, the rms particle velocity, urms, must be equal to the rms piston velocity. From Eq. (3.19),…

Consider the case again of the oscillating piston in Figure 3.1. We shall consider the sound energy that is produced by the oscillating piston, as it flows along the tube from the piston source. We observe that the wavefront and the sound energy travel along the tube with velocity c metres/second. Thus after one second, a column of…

We see that for the one‐dimensional propagation considered, the sound wave disturbances travel with a constant wave speed c, although there is no net, time‐averaged movement of the air particles. The air particles oscillate back and forth in the direction of wave propagation (x‐axis) with velocity u. We may show that for any plane wave traveling in…

As the piston vibrates, the gas immediately next to the piston must have the same velocity as the piston. A small element of fluid is known as a particle, and its velocity, which can be positive or negative, is known as the particle velocity. For waves traveling away from the piston in the positive x‐direction, it can be…

With sound waves in a fluid such as air, the sound pressure at any point is the difference between the total pressure and normal atmospheric pressure. The sound pressure fluctuates with time and can be positive or negative with respect to the normal atmospheric pressure. Sound varies in magnitude and frequency and it is normally…

The propagation of sound may be illustrated by considering gas in a tube with rigid walls and having a rigid piston at one end. The tube is assumed to be infinitely long in the direction away from the piston. We shall assume that the piston is vibrating with simple harmonic motion at the left‐hand side…

Some of the basic concepts of acoustics and sound wave propagation used throughout the rest of this book are discussed here. For further discussion of some of these basic concepts and/or a more advanced mathematical treatment of some of them, the reader is referred to the Handbook of Acoustics [1] and other texts [2–18] which are also…

The fluid mechanics equations, from which the acoustics equations and results may be derived, are quite complicated. However, because most acoustical phenomena involve very small perturbations from steady‐state conditions, it is possible to make significant simplifications to these fluid equations and to linearize them. The results are the equations of linear acoustics. The most important…