15,734 Hz

[vakkotaur]

15,734 Hertz is the frequency of a television's horizontal scan, at least NTSC (the current US analog TV standard). It's within the range of human hearing, at least for those with healthy ears that haven't been abused. And if things are as they should be, those two facts won't come together.

Alas, not everything is always as it should be. A TV with a traditional picture tube (rather than an LCD or plasma display or such) needs a transformer to deal with the horizontal scanning and this can be a problem. A transformer isn't just wires wrapped around metal, but usually wires wrapped around a bunch of pieces of metal insulated from each other. If the thing is old or just cheap, it can "sing" as a strong signal goes through it, vibrating all those bits of metal.

The result is an annoying high-pitched squeal or shriek that not everybody can hear. It can lead to conversations like this:

"The TV is on."

"No it isn't."

"Can't you hear it?"

"No."

"You must be going deaf."

"You're just hearing things."

It's not just TVs that have this. Computer monitors, at least older ones, can have this problem as well, though often at a different pitch. Such sounds are often on the edge of hearing and seems more sensed than outright heard. I used to walk into a school computer room where everything was supposedly off... and walk right to the one monitor that had been left on as it was, to me, screaming.

Comments

[fiddledragon]

heh - yeah - it's particularly annoying, and I can "hear" it from the foyer...and yeah - it is more sensed than heard, in my experience.

[malterre.livejournal.com]

I "hear" your pain. My husband makes fun of my "bear-like" qualities because not only can I sniff stuff out, I hear monitors and Television sets get turned on, not only in our apartment, but our neighbor's.

[kiwihunter8.livejournal.com]

I hear those things too, occasionally!

[chakawolf.livejournal.com]

I used to be able to hear them, but years of rock concerts and big rifles have given me a permanent TV Horiz. sweep ringing in my ears. For me, th eTV is *always* on.

Transformers don't have to have loose laminations to sing. There is also magnetostriction -- the A.C. field causes the core to change shape slightly. The bigger the transformer the louder the hummmmmmm.