rogers@wlf.isi.edu (Craig Milo Rogers) (11/30/89)
In article <4300@helios.ee.lbl.gov> mikec@ux1.lbl.gov (Mike Chin) writes: >Why is 20 kHz bad? I vaguely remember an article in Powertecnics describing >this system, but I wasn't aware of any controversy. (begin unsubstantiated opinion mode) Electric circuit components tend to vibrate and couple acoustically to the air at 20kHz much more than at 400Hz or 60Hz (or DC). 20kHz is within the "normal" human hearing range. Without *lots* of special design and fabrication attention, the proposed 20kHz design would "shriek" like an television monitor (horizontal retrace frequency of about 16kHz) or an FM stereo receiver lacking a good stereo pilot signal (about 18kHz ?) filter. Most adults I've met can no longer hear this high, but this doesn't mean that continuous, high-intensity exposure to these frequencies won't have a physiological effect on them. Some, such as I, retain the ability to hear this high; this is one of the reasons I avoid television and cheap stereos. A 20kHz acoustic vibration might, in turn, affect the results of biological or microgravity experiments aboard the station. (end unsubstantiated opinion mode) Does anyone out there know whether the team(s) that propose and evaluate power supply designs for the space station receive input from an operations team (for the medical effect of power supply configurations on the stationauts) or the science teams (for the effects of the power supply on the proposed scientific payloads)? Craig Milo Rogers