Why do emergency detectors use high pitched sounds?

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Discussion Overview

The discussion revolves around the reasons why emergency detectors, such as carbon monoxide detectors, utilize high-pitched sounds. Participants explore various aspects including human hearing capabilities, sound frequency characteristics, and the effectiveness of different alarm sounds in alerting individuals.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants note that as humans age, their ability to hear high-pitched sounds deteriorates, raising questions about the effectiveness of high-frequency alarms.
  • One participant suggests that shrill sounds may carry farther than lower frequencies, prompting further inquiry into sound propagation.
  • Another participant mentions that smoke detectors typically operate around 3 kHz, which is within the peak sensitivity range of human hearing.
  • There is a discussion about the logarithmic nature of hearing and how different frequencies are perceived, with some arguing that a couple of kHz is still considered low on the human hearing scale.
  • Participants speculate that high-pitched sounds may be more intense or annoying, potentially prompting quicker responses from listeners.
  • Some express that the choice of frequency may be influenced by the mass production of devices, which aligns with the frequency range most audible to humans.
  • Concerns are raised about the effectiveness of alarms for the hearing impaired, with references to manufacturers creating specialized alarms.
  • One participant mentions that lower frequency alarms require larger speakers to achieve the same volume, which could influence design choices.

Areas of Agreement / Disagreement

Participants express a range of views on the effectiveness and rationale behind high-pitched sounds in emergency detectors. There is no consensus on the best explanation, and multiple competing theories are presented.

Contextual Notes

Some participants reference external sources and studies regarding alarm effectiveness, indicating a broader context of research on sound frequencies and human hearing. However, specific assumptions and limitations regarding the effectiveness of high-pitched sounds remain unresolved.

newjerseyrunner
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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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Maybe because shrill sounds carry farther than lower frequencies?
 
phinds said:
carry farther than lower frequencies?
Do they? Google "elephant communication."
 
Bystander said:
Do they? Google "elephant communication."
Yeah, I googled around a bit. Turns out I apparently had it backwards.
 
Shrill is maybe 1 or 2 kHz? That's well within the peak of human hearing.
 
Smoke detectors aren't that high of a frequency. I believe they commonly use a frequency around 3 kHz.
 
phinds said:
?

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.
 
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Vanadium 50 said:
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 everything over a couple of KHz sounds high pitched but is still audible.
 
  • #10
phinds said:
I'm just saying ... the human range of hearing goes up to 20KHz, so a couple of KHz is low on that scale. Maybe everything 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
newjerseyrunner said:
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:
Janus said:
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
LOL, nope, nope, nope.:smile:
newjerseyrunner said:
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
phinds said:
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.

berkeman said:
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
Simple and solid state construction probably helps as well.
 
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  • #15
Vanadium 50 said:
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:
 
  • #17
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  • #18
newjerseyrunner said:
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...
 
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  • #19
Lower frequency alarms need bigger speakers to achieve same volume.
 
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  • #20
if i remember right the resonant frequency of the human ear canal is around 3khz, so I am 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.
 
  • #21
Rive said:
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.
Well, since birds already got mentioned - http://users.aber.ac.uk/rmm/urbansong.htm
 

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