Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: computer whistle

Learn more physics!

Most recent answer: 10/22/2007
Q:
My hearing aids pick up a high frequency sound when I sit in front of a computer monitor. What frequency am I liable to be hearing?
- David (age 71)
Detroit, Mi, USA
A:
We've often found pickup from CRT monitors in the 12 kHz range. I guess that it corresponds to some rate at which a beam scans back and forth across the screen. Maybe there are other rate in that range for modern LCD monitors.

Mike W.

The horizontal scan frequency of most TV sets is about 15.7 kHz.  Computer monitors can have a wide variety of frequencies, 15.7 kHz,  32 kHz or even higher.  Only dogs can hear  them. The internal circuits generating the driving voltage can emit some EM radiation with these frequency components that can be picked up by your hearing aid.  Also some subharmonic generation in your hearing aid that could downshift the frequency to 8 kHz, more likely to be audible.    In sum, there are a variety of explanations why your particular computer monitor and your particular hearing aid conspire to give you your particular sound.  As an experiment, try going close to your TV set to check out if you hear something.

Lee H

(published on 10/22/2007)

Follow-up on this answer.