Abstract
This study presents a development on a time efficient approach to measure the Acoustic Impedance of Industrial Insulating materials using an impedance tube with single moveable microphone and a white noise generator. The standing wave method is used to measure the acoustic properties (absorption coefficient and acoustic impedance) of sound absorbing materials. In order to use a burst of white noise instead of individual stationary sine waves, a signal processing technique was developed. The algorithm is based on the equation of simple harmonic motion, but uses distance as a variable, instead of time. This innovative method allows measuring at frequency resolutions as low as 5 Hz in a reasonably short amount of time. This is an advantage, as the classical standing wave method uses frequency resolutions of one-third of octaves for measurements, as otherwise time would be prohibitive. Experimental results are validated with those measured with the sine wave generator using one-third of octave frequencies by comparing their behaviours.
Highlights
The world is full of vibrating objects that order the motion of longitudinal pressure waves in the air [1]
Software measurement of a sample at a given frequency is done twice, one is to measure the pressure minima while the second is to measure the pressure maxima, while with the white noise generator software only one set of measurement is taken for the selected frequencies from 0 Hz to 6500 Hz with 5 Hz resolution and distances from 0 to 90 cm
A material with a low acoustic impedance will hinder the movement of sound energy less than when a high acoustic impedance is allowed to passed through a medium, this means that the higher the acoustic impedance the lower the absorption coefficient of that sample
Summary
The world is full of vibrating objects that order the motion of longitudinal pressure waves in the air [1]. Perceived by Humans as sound which, when unwanted and disturbing, is designated noise. Noise is a characteristic of many activities and processes and is present in most industrial areas. The uncontrolled level of noise that the human ears may be exposed to is capable of impairing human. Industrial processes and machinery include different sources of noise such as those from gears, compressors, pumps, conveyors, rotors, fans, stators, electrical machines and internal combustion engines [3]
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