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Gr. 9 Sc. Fair Project: New Questions

Dear All:

Here are my new questions!

1.      When I asked about the effect of soft tissue lining an airway passage,
one of you wrote to me suggesting that "... the impedance mismatch between
air and either hard or soft tissue is so great that hard vs soft probably
makes no significant difference ... [and that I should only] consider the
dimensions of the cavity."  Does anyone have an opinion on this?

2.      I understand that impedance is the resistance of a medium to the passage
of sound.  Is the impedance of air what causes a slight difference between
the length of an organ pipe and the length of the air column which vibrates
inside it? 

3.      I have read an article in the National Geographic ("Elephant Talk"
by Katherine Payne; Aug. 1989) from which I got the following points:
a)  Elephants are able to produce frequencies as low as 30 Hz.  Humans
standing nearby are unable to hear these sounds.
b)  The low frequencies are not accompanied by higher harmonics. (I assume
this means that elephants can control their vocal cords to produce a single
pure frequency.)
c)  The low frequencies can be detected by other elephants up to at least
2.5 miles away.
d)  The elephants amplify these low frequencies by using their trunks as
resonating air columns. (This is similar to what happens in an organ pipe.)
e)  The elephants use the low frequency vocalizations to coordinate the
movement of widely spread out herds.  Females use them as mating calls.
Adults of both sexes use them to relay distress calls from baby elephants.

If I assume that the elephants are using open air columns, the fundamental
resonant frequency occurs when the air column is one half the wavelength of
the sound.  (L = v/2f)  For a frequency of 30 Hz, this means that the air
column must be 5.7 metres long.  I haven't seen an elephant trunk that long.
Even if the throat is added on, I don't see how I can account for the
frequency in this way.

I have three hypotheses for this problem:
i)  The distance down to the lungs must be included in the length of the air
ii)  The elephants are somehow using their airways as closed air columns.
(This would cut the needed length in half.)
iii)  The elephants are producing the sounds by forced resonance rather than
natural resonance. (This would be similar to forcing a child's swing to move
by pushing while hanging on rather than letting go and waiting for the swing
to come back.  A similar effect is produced when the handle of a tuning fork
is pressed against the surface of a table.)

Does anyone have any ideas on this?  Does anyone have an e-mail address for
Katherine Payne?

5.       I've now read in several places that Parasaurolophus was able to
vocalizations at a frequency of about 10 Hz.  For an example, see
http://www.abqjournal.com/fleck/fleck1.htm  With my PVC model, I am unable
to produce resonance below a frequency of 50 Hz.  What am I missing?

Della Drury