What Ductwork Silencers Can
and Cannot Achieve


            Ductwork silencer is provided in air distribution system to attenuate the noise of the air stream being delivered, i.e. the noise level of the air stream at the outlet of the silencer should be less than that at the inlet.  However, the provision of ductwork silencers only may or may not be adequate to serve the intended purposes under different situations.

2.         Figures 1 to 3 illustrate how effective ductwork silencers can help in reducing the noise level at different locations.

Figure 1

3.         The silencer provision in Figure 1 above has no effect in lowering the noise level inside or outside the room or next door due to break-out noises from the fan and ductworks between the silencers and the fan, and noises break into the ductworks connecting to the exhaust louvre and adjoining area, and through the louvre blanking plate.

Figure 2
Figure 3

4.         The arrangement in Figure 2 helps to lower the noise level outside the room and next door by preventing noises from breaking out to the outside and the adjoining area, while that in Figure 3 can achieve lower noise level everywhere through the use of acoustic fan enclosure and silencers.  Obviously the latter arrangement is more expensive.

5.         It is important that a system designer is well aware of the purpose(s) his/her design needs to serve when putting in noise attenuation means to achieve the end and also cost effectiveness.

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