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FIG. 6.6.3 Reducing friction of rotating and sliding parts to decrease noise radiation.

(a) Static Unbalance (b) Dynamic Unbalance

Black blocks are heavy parts of rotor that cause vibration. ^^ White blocks are locations where counterweights must be placed to eliminate the vibration.

FIG. 6.6.4 Effects of static and dynamic unbalance on rotor operation.

dB, or roughly one-quarter to one-half of the original loudness. Air speeds less than 3 m/s measured at a supply or return grille produce a level of noise that usually is unnoticeable in residential or office areas. To reduce air speed in a given system operate lower motor or blower speeds, install more ventilating grilles, or increase the cross-sectional area of the existing grilles.

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