Once we have this measurement, we can apply silencing techniques, insulated wraps, sound enclosures, or whatever is required in order to reduce the noise of the fan. Then we would back calculate the sound power level at a specific distance used for the sound pressure level measurement:įan Sound Power Level (L w) = Fan Sound Pressure Level (L p) + Delta (Room Effect) The only practical way to arrive at a Sound Power Level (L w) is to take Sound Pressure (L p) readings at each of the eight octave band center frequencies in a laboratory setting. In general terms Sound Power Level (L w) cannot be directly measured. However, there is a problem measuring the Sound Power Level (L w) of a fan. In order to determine fan noise, Sound Power Level (L w) is what the acoustic engineer needs-something that is constant all the time no matter what the fan’s operating environment might be. Sound Pressure Level (Lp), on the other hand, changes depending on the environment in which the fan operates. Sound Power Level (L w) is like the sound fingerprint of a fan. Sound Power Level (L w) = the logarithm of the ratio of the actual power of the sound to 10(-12) watt reference. Sound Pressure Level (L p) = the logarithm of the ratio of the actual pressure to a common reference value of 0.0002 microbars There are four (4) very common terms used in acoustics:ĭecibel (dB) = one-tenth of the logarithmic unit (Bel) by which noise is measured and evaluatedĭBA = A convenient single number low frequency weighted dB scale for judging the loudness of a sound that more closely correspond to the threshold of hearing of the human ear. For example, a fan operating inside an uninsulated building is going to seem much noisier with its sound bouncing off the walls like reflections off a mirror than the same fan operating in the middle of a Texas cattle ranch. Aside from the design of the fan, speed of the fan, pressure the fan develops, volume of air going through the fan, there are external factors such as the environment in which the fan operates. I may like classic rock & roll music, but to someone else-it’s just noise.ĭetermining how noisy a fan is and what to do about it is not as straightforward as one might think. Noise is relative to the ear of the listener. So, what’s the difference between sound and noise? Simply stated, noise is unwanted sound. Fortunately, sound is governed by natural laws so we can measure, predict, and use it to our advantage just like the fan performance is governed by the Fan Laws. Interestingly, “sound happens” whether or not anyone is around to actually hear it.
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