In article , Robert Green wrote:
"mm" wrote in message
news
On Sat, 3 Oct 2009 11:27:35 -0400, "Robert Green"
wrote:
I was at an elderly friend's house the other day when the smoke alarm
went
off. It was quite loud and I reacted instantly to the noise. My friend,
a
former Army marksman in his 70's, who's suffering from profound high
frequency hearing loss, heard nothing!!!
Then I started looking around for alarms that used lower frequency
sounders
but the only thing I could find were specially converted smoke detectors
that cost $300!!!!
I'm wondering why COTS alarms operate at such a high sound frequency,
They do? I have an AC smoke alarm and I've had a couple battery ones,
and they seem to be mid-range. (I've played the piano for 50 years,
but still have little idea what note they are, or even what octave,
but they still seem midrange. I'll guess, middle C. The nearby A is
440, so C must be 500 to 550 cps.)
I believe that the frequencies used by current smokes are in the 3000Hz
range. However, there seems to be quite a difference between battery and
line-powered smokes and the tones they create.
It sounds like a metallic kazoo, or a trombone at its mid-pitch.
especially when it's well known that older adults lose their high
frequency
hearing first. I have been thinking of just unsoldering the Sonalert
sounders in low priced alarms and replacing them with lower frequency
SNIP from here to edit for space and concentrate on line-vs-battery point
I have experience with line-powered smoke detectors and other devices
that I actually designed and built having similar audible tone.
My experience suggests that line powered smoke detectors with a buzzy
tone have most of their acoustic spectrum around/above 2500 Hz and
probably nearly enough all of it above 2000 Hz.
My experience suggests that the frequency difference between the loud
harmonic components makes a low fundamental frequency apparent despite
lack of significant presence of the fundamental frequency and the first
few, quite a few even, harmonics.
- Don Klipstein )