Category: 7. Noise and Vibration Transducers, Signal Processing, Analysis, and Measurements

At low frequencies, for example, below about 1000 Hz, the frequency response of a microphone is independent of the angle of incidence of the sound waves. However, at higher frequencies, as the microphone dimensions and the wavelength of the sound become comparable, diffraction effects become important and the frequency response of a microphone is strongly dependent on the…

Since the human hearing range extends from about 20 to 20 000 Hz, it is desirable that the frequency response of microphones and noise measurement systems should be “flat” between these limits as shown in Figure 7.6. For certain types of measurements (e.g. for measurement of sonic booms or explosive blasts), it may be necessary to measure sounds that…

The magnitude of the frequency response, R(f), of an ideal microphone is given by Eq. (7.2a) as the frequency of the sound pressure p is changed. The magnitude of the frequency response, R(f), or an ideal accelerometer is given by Eq. (7.2b) as the frequency of the vibration a is changed. Figure 7.6 shows the frequency response of an ideal microphone used for noise measurements or an ideal accelerometer used…

It is seen for the microphone (or accelerometer) shown in Figure 7.3 that the dynamic range is about 100 dB. Most good‐quality microphones have a dynamic range of about 100–120 dB (interestingly enough about the same as the human ear) [2]. As the microphone diaphragm diameter (or accelerometer mass) is increased, the transducer sensitivity is normally increased as well…

An ideal microphone (or accelerometer) together with its measurement system should have an output voltage amplitude E that is proportional to the exciting pressure amplitude p (or acceleration amplitude a) (see Figure 7.2). The ratio of open‐circuit output voltage to input pressure (or acceleration) is normally called the sensitivity Mp: (7.1) The transducer sensitivity [V/(N/m2) or V/(m/s2)] depends on the microphone (or…

An ideal sound or vibration transducer should have the following characteristics [1]: No transducer can meet all of the above criteria, and thus different types of transducers and vibration sensors are preferred for different measurements. The microphone is by far the most common form of acoustical transducer, and the piezoelectric accelerometer is the most widely…

The basis of all noise and vibration measurement systems is the transducer. The microphone is the main transducer used to measure sound, while the accelerometer is the main transducer used to measure vibration. Specialized transducer systems have been developed to measure sound intensity in air and vibration intensity of structural systems. In addition, measurement procedures…

It may be necessary to measure noise and/or vibration for various reasons. Before beginning any measurement program, the objectives should be defined. For instance, it may be desired to measure noise to determine if a noise problem exists, whether the noise output of a machine is within its specifications, to determine the main sources of…

In the measurement of noise and vibration fields, it is necessary to sense the sound or vibration disturbance with a transducer. The transducer converts some physical property of the sound and vibration field into an electrical signal. This signal is then amplified, attenuated, or transformed in some way so that it can be analyzed and/or…