Why a high pitched beep?

  • #1
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I know that as humans age their abilities to hear high pitched deteriorates, even if the rest of their hearing doesn’t. So why do emergency things like CO detectors use such a high pitched sound? I got to my in laws and their detector needed new batteries. Neither are hard of hearing but neither had any idea their detector was going off. Made me wonder if they’d even be able to hear it if it went off for real?
noises
 
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  • #2
phinds
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Maybe because shrill sounds carry farther than lower frequencies?
 
  • #3
Bystander
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carry farther than lower frequencies?
Do they? Google "elephant communication."
 
  • #4
phinds
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Do they? Google "elephant communication."
Yeah, I googled around a bit. Turns out I apparently had it backwards.
 
  • #5
Vanadium 50
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Shrill is maybe 1 or 2 kHz? That's well within the peak of human hearing.
 
  • #7
Drakkith
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Smoke detectors aren't that high of a frequency. I believe they commonly use a frequency around 3 kHz.
 
  • #8
Vanadium 50
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???

That's very low on in the range of human hearing:
You're misreading something. 1.76 kHz is two A's above middle C.
 
  • #9
phinds
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You're misreading something. 1.76 kHz is two A's above middle C.
I'm just saying ... the human range of hearing goes up to 20KHz, so a couple of KHz is low on that scale. Maybe everthing over a couple of KHz sounds high pitched but is still audible.
 
  • #10
Janus
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I'm just saying ... the human range of hearing goes up to 20KHz, so a couple of KHz is low on that scale. Maybe everthing over a couple of KHz sounds high pitched but is still audible.
In terms of octaves, the human range is 11 octaves with 2 kHz falling in the 7th octave.

Also, the (normal) human ear is most sensitive to the 2-5 kHz range, so it would make sense to place an alert tone in this range.
 
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  • #11
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So why do emergency things like CO detectors use such a high pitched sound?
Interesting question, which makes me think of many alarms clocks which also have (relatively) high pitched sounds. I wonder if it is beacuse it sounds more intense/is more annoying, so the listener is more inclined to take action or even wake up?

EDIT:
Also, the (normal) human ear is most sensitive to the 2-5 kHz range, so it would make sense to place an alert tone in this range.
Sounds like a good reason.
 
  • #12
berkeman
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LOL, nope, nope, nope.:smile:
I know that as humans age their abilities to hear high pitched deteriorates, even if the rest of their hearing doesn’t. So why do emergency things like CO detectors use such a high pitched sound?
There is a practical reason for this, but it has little to do directly with the best range for human hearing...
Small, inexpensive piezo-based sound makers for low-cost consumer electronics happen to have that frequency range. You are not going to spend several dollars for a speaker-based sound maker in a product design, when you can use a simple sub-dollar piezo beeper instead... :smile:
 
  • #13
Vanadium 50
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the human range of hearing goes up to 20KHz, so a couple of KHz is low on that scale.
Ah, here's the thing you are missing. Hearing is logarithmic. Each octave is a factor of two in frequency.

There is a practical reason for this, but it has little to do directly with the best range for human hearing...
I suspect the reason the devices are inexpensive is because they are mass produced in the range that is best for human hearing.
 
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  • #14
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Simple and solid state construction probably helps as well.
 
  • #15
berkeman
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I suspect the reason the devices are inexpensive is because they are massed produced in the range that is best for human hearing.
Just a commercial goodness coinkidink. :smile:
 
  • #18
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So why do emergency things like CO detectors use such a high pitched sound?
In theory, because it is out of the range of the most commonly used frequencies. Usually apart from some bird songs there are not many sources for that range.

In reality, it is what @berkeman wrote under that spoiler button...
 
  • #19
CWatters
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Lower frequency alarms need bigger speakers to achieve same volume.
 
  • #20
if i remember right the resonant frequency of the human ear canal is around 3khz, so im guessing that has something to do with it as well..

i know when mastering a music track, its common to dip down the volume in that range.
 
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