ELECTRIC MOTOR NOISE BALANCING DEVICE Russian patent published in 2014 - IPC H04B1/28 

FIELD: electricity.

SUBSTANCE: device comprises two identical electric motors set in a chamber of small volume, input terminals connected to one electric motor via a narrow-band phase-shifting circuit, and a resistance-capacitance line of electrical delay connected between the input terminals and the other electric motor; the phase-shifting circuit is narrow-band one with the phase setting of 90° for network frequency of 50 Hz, and the electric delay line is made as a rheostat-capacitance circuit, the time constant of the electrical delay line is τ_e=RC, where R and C stand for active resistance and capacitive resistance of the rheostat-capacitance circuit respectively, and is equal to the time constant of acoustical delay τ_a=l/c, where l -stands for the distance between the electric motors along the chamber length, c - sound speed in the air.

EFFECT: improved efficiency of noise reduction in a wide frequency range.

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