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Gr. 10 Sc. Fair Project
I am sending this message to three mailing lists and to some individuals.
For those of you on the Vrtpaleo and Dinosaur lists, this message may have
less relevance, but any help you can give me will be greatly appreciated.
Over the months that I was doing my project on hadrosaur vocalizations, I
received two basic pieces of advice over and over again:
1. Without soft tissue it is not possible to come to firm conclusions
as to what frequencies hadrosaurs may have produced nor how they may have
produced such frequencies.
2. There are no living analogues to help deal with the first problem.
I have finally come to agree with the first of these but I do not agree with
If we are considering the airway from an animal's nostrils to the back of
its mouth, all that really matters, when we are looking for the fundamental
resonant frequency of the airway, is the length. It doesn't matter whether
the airway goes through a crest or some form of elongated snout. From this
point of view an elephant is a good analogue.
Those of you who have followed my last project will know that I have already
started to pay attention to elephants. I started with the idea of looking
for a hadrosaur analogue, but I've found that elephants are interesting in
their own right. Besides nobody can complain about missing tissue!
My new project will focus on elephants. I still have hadrosaurs in the back
of my mind. I'm still hoping that I can take some ideas about elephant
vocalizations and use them to speculate about hadrosaurs.
My present knowledge about elephant vocalizations can be summarized as follows:
1. Indian and African elephants can produce and hear vocalizations as
low as 14 Hz. Forest elephants are reported to produce frequencies as low
as 5 Hz, but this is not accepted by all workers in the field.
2. Some field observations suggest that elephants use low frequency
vocalizations to communicate over long distances. The distance varies from
3 km to 10 km depending upon atmospheric conditions. The best conditions
occur in dry weather in the late evening.
3. As far as I am aware, no one has previously looked at the way in
which the low frequency vocalizations are produced. (If I'm wrong, please
tell me now!)
I plan to look at three hypotheses for production of these vocalizations:
Hypothesis #1: Elephants use vocal folds alone to produce their vocalizations.
Hypothesis #2: Elephants use their bodies as seismic generators by shifting
their centres of mass.
Hypothesis #3: Elephants use their trunks and lungs together as Helmholtz
resonators. Vocal folds may or may not be the primary source of the
frequencies to be selected by resonance.
For some of the higher frequencies, 30 Hz and up, it is possible that
elephants use their trunks as closed (open at one end only) or as open (open
at both ends) air columns. I am also aware that the air spaces in the skull
might be used to produce lower frequencies without involving the lungs.
I still don't know how I'm going to test Hypotheses #1 and #2, but my plan
for #3 is as follows. Since the mathematical formula for a Helmholtz
resonator assumes a container with rigid walls, I have to build a model with
soft walls to simulate the lungs and see how well the calculations stand up.
I have one source of encouragement here. In "The Science of Sound", a book
recommended to me by several people on the Bioacoustics List, it is stated
that the flexible sides on the sound box of a guitar cause the resonant
freqency to be lowered. This was exactly what I wanted to hear!
The design of my model exists only in my mind but I plan to build a
cylindrical wire frame. Over the frame I will place several layers of
plastic garbage bags. In the bottom of the bags I will place a layer of
gravel to simulate the branching which occurs in the lungs. (Thank you to
Dr. Marty Michener for the idea of using gravel.) The top of the bags will
be sealed around a rubber hose. The whole contraption will then be immersed
in a barrel of water. Finally, I will use my home-made frequency generator
and a borrowed oscilloscope to find which frequencies produce resonance.
Now, I have some questions:
1) Can anyone see a major problem with the design of my soft-sided
Helmholtz resonator? Can anyone suggest improvements?
2) How should I test my first two hypotheses?
3) Do I need a special microphone to detect frequencies from 4 Hz to 300
Hz? How much is this likely to cost?
4) What is the volume of the pneumatic cavities of an elephant skull?
5) What volume of air is in the lungs of an elephant? Where can I find a
reference to answer this kind of question? (I already have several articles
published by Dr. Katherine Payne and by Dr. Rickey Heffner. These were sent
to me by the authors.)
6) What diameter of rubber hose should I use in my Helmholtz resonator? I
plan to use two different lengths of hose to simulate the throat alone and
the trunk and throat together. So, how long is an elephant's throat? (By
throat, I guess I mean the distance from the mouth to the lungs.)
7) Is there some upper limit on the sound power which could be generated by
vocal folds working alone?
8) How much help are vocal folds likely to get from forced resonance if
natural resonance does not occur?
9) When an elephant vocalizes, is the mouth open or closed?
10) Would sound analysis software be of any use in my new project?
Any help will be apreciated.