Prezelj J., Cudina M.

Typical noise spectrum of cooling fan consists of a broadband noise superimposed by pure tones, mostly at the fundamental and the harmonics of the blade passing frequency. To reduce such noise several types of silencers can be used. Active noise control is an attractive up to date method, which can be used for narrow band and broadband noise control. With a typical secondary monopole source only a local noise reduction can be achieved. Reduction of noise propagation with a side branch resonator is well known method, which is easy to apply. With this method a significant reduction of narrowband noise propagation can be achieved. This article desribes, how these two methods could be combined to achieve global noise reduction. A practical analysis of noise reduction on three different cooling fans with different side branch resonator configurations is presented. Influence of additional side branch resonator on fan efficiency is practically investigated. Experimental results show, that a suitable design of side branch resonator can improve the efficiency of axial fan and reduce noise level at the same time.