The discussion we are having on sound sources to be used as a travel aid
is fascinating. Yet, I wonder if any sound generator would receive wide
enough acceptance to be worth any effort. As a group, we are pretty
skeptical of travel aids. Yet, this doesn't seem to stop me from
throwing out ideas.
First, my feeling is that there is really no problem with creating a
sound for long echos such as when one is outdoors or in a large lobby or
auditorium. One can usually get away with a hand clap or an extra loud
cane tap. Where I see a potential need is for short echos that give
information about the environment immediately around you, that power
pole mentioned elsewhere, or that overhanging branch or sign. We have
concentrated on specific frequencies, but I have had some success in
getting nice reflections with high frequency noise. I first noticed
this possibility at work where an air vent near my desk was so
constructed as to generate a high frequency hiss rather than a general
rushing sound. This sort of "hiss" is likely less noticeable or
"socially offensive" to those around us as well. Remember, though, that
if you experiment with an FM radio, a good noise generator between
stations, that there is a de-emphasis circuit that has the affect of
reducing the high frequency portion of noise. Also, steady noise
probably wouldn't give as much distance information as would some kind
of pulsed or modulated noise.
The ultrasonic idea intreagues me. It sounds a little like the
principle used in the Sonic Guide, or whatever it is called now. It
generated a sweeping ultrasonic tone and mixed the reflected sound
with the original to create an audible tone. The longer the delay of
the reflection, the greater the difference in frequency and the higher
the tone. However, one could only here the resulting difference using
the earphones of the Sonic Guide, even though the original and
reflected ultrasound must have set up some wave interference patterns.
I suspect, therefore, that there is some physical reason that audible
sound cannot be produced from the interference of two ultrasonic
reflected signals. It might be interesting to try, though.
Thanks for listening.
National Federation of the Blind
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