I was wondering about this and couldn’t seem to phrase a query right in Google to find the right information, so here I am. What causes that high whine that rises in pitch when you turn on some electronic devices? I don’t mean the near-ultrasonic noise you get from CRT screens, it’s more of a charging-up sound (at least, that’s what I’m picturing). It starts relatively low in pitch and then rises until you can’t hear it anymore. For those of you who are gamers, perhaps you may remember this sound as the sound that you’d hear when activating Sam Fisher’s night-vision goggle array in the Splinter Cell game series.
So what causes it? If I wanted to build a device to deliberately make this noise when powering on, what component(s) would I have to include? Thanks in advance.
Thank you, CR! I don’t know how I didn’t find that physlink article, as I searched for very nearly that same question, except for the camera flash unit part. Thanks again.
If I may piggyback–what about the “near-ultrasonic noise you get from CRT screens”? I’ve always wondered about that. It was something I could hear as a kid, but everyone else (including kids) would act like I was crazy.
I heard it too (from screens and some other electronic gadgets); a very distinctive, very high pitched electronic tone. It’s like bat screeches I guess; something just on the edge of human hearing, so only some children can hear it and even they lose the ability over time.
Standard-def TVs in North America use the NTSC standard, which draws 525 lines every 1/29.97 seconds. This means the electron beam swings back to draw a new line at a rate of 15.734 kHz. And just like the charging flash example, CRTs have components that emit sound when something changes, and so they emit noise at that frequency.
Human hearing has a limit of about 20 kHz, but this is for young, healthy ears, and the limit degrades over time. So while many/most kids can hear the 15.7 kHz easily, lots of adults cannot. Not to mention kids that have damaged their hearing via loud music.
It’s caused by the same basic thing as the flash. It’s a high frequency transformer that is physically vibrating at a frequency that you can hear. In the case of a CRT it’s a specific part called the flyback transformer, which controls the horizontal movement of the electron beam in the cathode ray tube (aka CRT).
The flyback transformer often operates at frequencies which are right near the top end of the human hearing range, so some folks will hear it and some folks won’t.
High frequency transformers are used in a lot of things these days, especially higher power devices since a high frequency transformer can be made smaller and lighter than a low frequency transformer.
I used to hate going into electronics stores because the noise of all those components at slightly different frequencies was so annoying that it almost hurt. Also made me feel like my teeth itched. And I was one of those kids who could hear bat screeches. Even in my late 30s I can still hear mosquito devices. A few years ago, a couple of places in Ginza were using them and I’d have to divert around them. They either have stopped using them, or my hearing is turning to shit finally.
I think the Ghostbusters’ Proton Packs had the classic charge-up whine.
Hear a sample about 25 seconds in:
Some truck docks have these ‘ultrasonic’ bird repelling devices that basically chirp and screech all day and night. I can hear them quite annoyingly clearly but I’ve never met anyone else who can. http://www.bird-x.com/quad-blaster-qb4-p-13.html
Silent… my ass.
