I haven't read the last few messages about cane tips and their
sounds, but here are my two cents'worth.
In 1963-65, when I was in the middle of learning cane travel in
high school, I was really sold on the Rainshine canes we were
beginning to use at the Iowa Commission for the Blind, in
comparison to the crook-handled aluminum canes with nylon tips
that were and sometimes are the favorites of the O&M
professionals. One of the primary problems with the aluminum
canes, as far as I was concerned, was the sound. As you went
down the sidewalk, they didn't tap, they bonked. Although the
nylon tip was a rather inert material, much of the vibration was
transmitted into the aluminum shaft of the cane, which was
undamped and rang like a bell at a few frequencies in the
hundreds of Hertz. The cane rang with several noticeable
pitches, meaning that the radiated sound persisted for perhaps 50
or 100 milliseconds. With sound traveling at about 1100 feet per
second, this meant that the wave train coming from the cane was
50 or 100 feet long, far too long to resolve objects and distances
of a few feet. This cane was obviously designed by people who
had no appreciation for the role of sonar in travel by blind
people.
The Rainshine canes, and the hollow fiberglass NFB canes that
followed them beginning in 1975, have a small metal tip with a
fundamental resonant frequency somewhere around 5 kHz. This
frequency shifts a little as the tip wears, but this is of little
prractical importance. The vibration of the metal tip is heavily
damped by the rubber around it; so much so that its natural
ringing dies out in just a few cycles. Instead of a ding, you
have a sharp click, centered around 5 kHz, with a bandwidth of a
couple of kHz, and lasting only a millisecond or two. (I haven't
measured this, but this is my best guess of duration and
frequency based on the sound these canes make on cement). This
click or pulse, since it is only a few milliseconds long, is also
only a few feet long, and can resolve much smaller and more
relevant features in the environment.
I know that sonar is not important to everybody. As my hearing
will diminish, and as I travel on cushioned surfaces or in noisy
environments, other cues must be employed. I just don't want
to see us develop a new tip that ignores sonar. I think a rather
broad range of parameters would be acceptable and useful to most
travelers, and I don't think we need to develop a special
clicker, especially when finger-snapping and other methods can be
used when absolutely necessary (such as out in the wide expanses
of snow we had around here last week.) I bring the subject up
now because I feel we already lost some good sonar
characteristics in the telescoping and carbon fiber canes. Too
much of the tip vibration is carried up into the shaft and
re-radiated by these canes, so the click is accompanied by lower
frequencies that last longer and sometimes mask important echoes.
A good cane is hard to make, but we can do it.
Lloyd Rasmussen
lras@loc.gov
l.rasmussen2@genie.com
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