A Comparative Study of Performances of Different Types of Barrier Constructions for Attenuating Low Frequency Noise

Abstract

Low Jrequency sounds ancl vibrations are associated mostly with rotcuy machine.s, w'hich are the most common ones, seen.from w*orltpldces like factor7t lathe machines, milling machines, etc., to machineries like pwnps, fans. generators etc., to vehicles like cars, trains, airplanes etc., in one words, almost everywhere. Wen the sound pressure level oJ'these lotu frequency sounds is not within a tolerable range, it is considered as noise and it must be control.led in order to protect human ear frorn its hazardous fficts. Low frequency noise can be controlled in many ways; one of the ways is restricting the noise from reaching human ear i,e. usirtg barriers. The problemfaced b1, barriers in re.ttricting oflowfrequency noises is that they have a high wavelength, making them likely to pass through barriers easily and less chance of reflection. Also, the absorption cctellicient oJ'a material is inversely proportional to the wavelength, therefore low absorption possibility .for low frequency noises. To ,solve these problems, the mass oJ the barrier is increased following mass low, which increases cost. In the present study, it has compared the transmission losses due to tw,o types of commonly used barrier constructions, Double layer type barriers and Sandwich ltpe barriers and determined which one has better performance in attenuating low frequency noise. Also, for construction, two dffirent types of absorbing materials, glass wool and PE foam is used to account for material variations.