Satisfactory applications occur when all aspects of the installation We in harmony with each other. Proper operation, constant monitoring, and maintenance are also part of the equation. Troubleshooting must be employed when one of these areas becomes a problem. Noise is generally considered low-quality, unwanted sound. The ears sense noise, whereas vibration is sensed by feel or touch. Sources of noise can usually be identified by some form of characteristic sound to which we can relate. Words such as tone, rattle, pitch, steady or unsteady, and intermittent are examples. These characteristic words help to define whether the source of the noise is aerodynamic, mechanical, or electrical. Aerodynamic generated noise is characterized by a continuous broadband frequency spectrum with a superimposed tone. The tone is typically objectionable when it becomes 4-6dB louder than the rest of the spectrum. The tone can be the blade frequency, which is a function of the fan type. It can become very objectionable when system effects and various controls cause it to rise higher than normal. Additional causes include turbulence, high velocities, and instabilities due to pulsation and surge.
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