SOUND MUFFLER
Some equipment in industry produces jarring noise while they run and eventually impair our ears. A method to attenuate such noise from equipment is described below. Before describing the concept, the lessons learnt in school Physics is recapitulated. The bell jar experiment may be referred. (Google search may be accessed). In the fore said experiment one calling bell is kept inside a bell jar and power supply is given. We can hear the bell sound from outside. Then gradually the inner space is evacuated and sound level decreases. This shows sound needs a medium for propagation. We know the velocity of sound is given by the equation a = ?(?RT). In evacuated condition the velocity and hence its intensity eventually reduces. A similar method can be adopted for reducing noise from running equipment. Referring Fig.1, a sound producing equipment (1) say like water cooled air compressor or a stationary diesel engine is shown. A broken section is given in fig.1 b. for visualization. The equipment is enclosed by an inner hood (2) as shown in the fig.1. An outer hood (3) encloses the inner hood (2). A nozzle (4) is fitted to the outer hood. The other end of the nozzle is connected to a small vacuum pump. The inter space between the inner and outer hood is evacuated as shown in fig.2. Hence the noise emanating from the equipment is suppressed by the inter vacuum and hence the noise is attenuated to the outsider. However the sound source (1) must be suitably isolated from flooring and to the surrounding hoods by rubber padding to damp out undue vibration. The inter space is suitably reinforced to prevent collapse of structure while vacuuming. Also the penetrations to the equipment like service water line, air line etc. penetrating from outside to inside through inner and outer hoods to the compressor may be suitably laid with acoustic sealant material. Two air tight doors (5) & (6) are provided to inner hood and outer hoods for inspecting the equipment periodically.