Small direct current (DC) motors are widely used due to their low cost and compact\nstructure. Small DC motors of various designs are available on the market in different sizes.\nThe smaller the motor, the more closely it may be used by individuals. Contrary to the size and\nsimplicity of these motors in terms of structural design, sources of motor noise and vibration can be\nquite diverse and complicated. In this study, the source of motor noise and vibration was visualized\nover a very wide range of frequencies. The particle velocity of the motor was reconstructed from\nnearfield sound pressure measurements of motor noise. In addition to noncontact measurements\nconducted on a motor running at constant speed, the particle velocity of a stationary motor due to the\nimpulse of an impact hammer was measured with an accelerometer. Furthermore, motor noise was\nmeasured under motor run-up conditions with different rotational speeds. As a result, by combination\nof these three methods, the sources of motor noise were accurately identified over a wide range\nof frequencies.
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