Carl Vangsness wrote: > Nibbling out the area contained by the holes in the front of the chassis > will reduce the noise by nearly 80%. Went from extremely annoying to > knowing the fan is on. >
This illustrates the point that the noise is primarily due to the dynamics of the airflow. If the fan's mechanics (eg. bearings) were making the noise it wouldn't last very long. Some fans are naturally quieter than others, that is due to the shape and size of the blades and their relationship to the housing. The better designs minimize pressure pulsations as the blades turn. It is still important to optimize the airflow paths for the inlet and outlet flows. Disruptions will cause turbulence, which will result in undesired acoustic energy. Nibbling out the extra metal in the SDR1000 case achieves this goal. I am reminded of the case of the Beloit paper machine. Back in the late 30's a new design of suction roll significantly improved the water extraction from the sheet, but at the cost of being extremely noisy. The roll used a lot of small holes on the surface, rotated very fast, and was under an internal high vacuum. The problem turned out to be the transition from vacuum to ambient air pressure at the hole boundaries. The physicist who determined the cause, and found a relatively simple solution, was a certain Dr. John Kraus, otherwise known as W8JK. Source: Big Ear, Kraus, John 1976 73 Alf NU8I Scottsdale AZ DM43an _______________________________________________ FlexRadio Systems Mailing List [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
