Hypothesis: Ultrasonic Frequencies May Cause Hearing Loss
Quote:
>Subject: Hypothesis: Ultrasonic Frequencies May Cause Hearing Loss
>Keywords: ultrasonic tinnitus hearing loss
>Date: Thu, 19 Jan 1995 16:23:43 GMT
>Yesterday I was working on a device which, among other things,
>uses pulse-width modulation at around a 30 kHz rate to generate
>audio. My low-pass circuit wasn't working yet, so I connected the
>device directly to the speaker. I was hitting it with around 5 V
>peak-to-peak, but the sound wasn't very loud because PWM isn't a
>power-efficient way to generate audio.
My experience with soundof this frequency dates back to grad school.
I was only exposed to it for a few seconds at a time, while the door to an
ultrasonic siren was open (we used to demonstrate catching cottton on fire
by positioning it over the siren - door closed - (most of the time).
At that time, I perception was of a mild "pressure" on ly eardrums when I
knew it was only the 30 kHz I was being exposed to.
Essentially I've had no more exposure than that. However, these days, I can
simulate that feeling by driving a pair of headphones with an audio
oscillator (if it puts out enough voltage)..
Quote:
> When I went to bed my ears were ringing loudly, at a high
>pitch.
> Hypothesis: Exposure to ultrasonic frequencies can cause
>tinnitus and/or hearing loss.
I think it can be considered to be just as damaging as some other sounds.
Quote:
>Obviously this is only anecdotal evidence and doesn't prove anything.
>But my ears tends to ring easily with exposure to loud noise (though
Was this "easy ringing" present before the 30 kHz exposures?
Quote:
>I haven't been having problems lately), so I may be a good test subject,
>sort of a canary in a coal mine.
How much time did you spend in "the mine"? How many hours per day and how
many days?
Quote:
>Once a company I worked at decided to install ultrasonic motion sensors
>to turn off the lights automatically after people left the room. We
>tested them with a sound level meter capable of hearing ultrasonics,
>and the sound levels we found (in the neighborhood of 95 dB) would've
It IS in violation since the limit is 85 dB in those octave bands, though
teh company can argure that ON THE AVERAGE it had been less than 85 dB per
shift.
Quote:
>Today I ran a medline search. I only found one relevant article, but it
>is suggestive.
It's still too early. Not only are MD's in a state of denial about
Tinnitus, but so also is the WHOLE industrial complex when it come to
ultrasonics.
Quote:
>Grzesik J; Pluta E
>Dynamics of high-frequency hearing loss of operators of
>industrial ultrasonic devices.
>Source: Int Arch Occup Environ Health 1986;57(2):137-42
>They found that exposure resulted in high-frequency hearing loss of
>1 dB / year. (Note: this doesn't necessarily apply to medical diagnostic
>ultrasound, which uses much higher frequencies (in the mHz range).)
Medical ultrasound does it stuff in a liquid medium (in vitro?).
Very little energy is coupled into the air. On the other hand, if one tries
to so an ultrasound on the skull near the cochlea, what can I day????
(I don't think it's done anywhere).
Quote:
>Ultrasonics are being used all over the place, for burgler alarms,
>motion sensors, etc. And ultrasonic pulse width modulation is often
Depends on the intensity: Registering more than 75 dB on a radio shack
meter, I'd be VERY wary.
Ang.
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