AMAZON multi-meters discounts AMAZON oscilloscope discounts
The frequency characteristics of noise from air-distribution systems are de scribed by the graph below. Airflow noise due to turbulence usually occurs at mid-frequencies from 250 to 2000 Hz. Fan noise (rumble) occurs at low frequencies (< 250 Hz), and air outlet noise (hiss) occurs at high frequencies (>1000 Hz). Because fan noise increases with static pressure, air-distribution systems should be designed to have minimum resistance to airflow. Low-frequency rumble (< 63 Hz) also can be caused by air turbulence that buffets duct walls. Example equipment noise levels in dB at octave-band center frequencies from 63 to 8000 Hz are given at the end of this section.
Note: Terminal boxes in air duct systems and fluorescent ballasts produce noise levels in the range of 125 to 1000 Hz. Noise from lighting ballasts can be amplified by the metal surfaces of luminaires and other surfaces free to vibrate with the ballasts. Consider remote mounting of ballasts for critical areas where low levels of sound are essential.
Next: Supply and Return Air Duct Layouts