Category: (((—Acoustics Engineering—))))

The passive noise and vibration control techniques discussed above work well at mid and high frequencies or in a narrow frequency range but often have the disadvantage of added weight and poor low‐frequency performance. Active noise and vibration control has proved useful in the solution of many of these problems. Although the principle of active…

An obstacle placed between a noise source and a receiver is termed a barrier or screen. When a sound wave approaches the barrier, some of the sound wave is reflected and some is transmitted past (see Figure 9.38). At high frequency, barriers are quite effective, and a strong acoustic “shadow” is cast. At low frequency (when the wavelength can equal…

Acoustical enclosures are used wherever containment or encapsulation of the source or receiver is a good, cost‐effective, feasible solution. They can be classified in four main types: (i) large loose‐fitting or room‐size enclosures in which complete machines or personnel are contained, (ii) small enclosures used to enclose small machines or parts of large machines, (iii) close‐fitting…

Sound‐absorbing materials have been found to be very useful in the control of noise. They are used in a variety of locations: close to sources of noise (e.g. close to sources in electric motors), in various paths, (e.g. above barriers in buildings or inside machine enclosures), and sometimes close to a receiver (e.g. inside earmuffs).…

Load‐bearing and non‐load‐bearing structures of a machine (panels) are excited into motion by mechanical machine forces resulting in radiated noise. Also, the sound field inside an enclosure excites its walls into vibration. When resonant motion dominates the vibration, the use of damping materials can result in significant noise reduction. In the case of machinery enclosures,…

Vibration isolation has been discussed frequently in the literature [50]. Vibration isolators are used in two main situations: (i) where a machine source is producing vibration and it is desired to prevent vibration energy flowing to supporting structures and (ii) where a delicate piece of equipment (such as an electronics package or precision grinder) must be…

Noise and vibration control should always be incorporated at the design stage wherever possible because there are more low‐cost options and possibilities then to make completed machines or installations quieter [1–3]. After machines are built or installations completed, noise control approaches can still be achieved through various modifications and add‐on treatments, but these are frequently…

The noise and vibration of some sources can be just annoying. Some sources, however, can be intense enough to permanently hurt people. Research on noise and vibration control is therefore very important and it has produced the development of multiple control approaches. It is widely accepted that noise and vibration control is most effective when…