Partial Hearing

[Jos]

Hi

Opening your mouth to a certain extent, certainly changes the resonant 
frequency of the mouth-cavity. This means that for a certain opening
angle of the mouth, certain frequencies are dampened less than others,
so your mouth cavity works as a filter for certain frequencies. If the 
characteristic dimensions of your mouth, from closed to fully open,
would
vary between 0.01 and 0.05 m, the resonant frequencies could be
estimated
to be multiples frequencies between 15000 and 3000 Hz. (the speed of
sound
being about 300 m/s) Considering the high frequencies, this would maybe 
only work for tuning in the treble.

The Eustachius tube could play a role as sound conductor, but also, in
hearing
there is a significant effect called 'bone conduction'. Sound
is guided by bone tissue to the eardrums. (by the skull in this case.)
This is also known to play a significant role in auditory localization 
of sounds (spatial hearing).

I might suggest an experiment here. In our lab, we performed so-called 
'putty experiments', in which we mounted moldable putty in the earshells
of test 
subjects (not occluding the eartube.) We did this, because it was known, 
that changing the acoustical characteristics of the external ear,
severely
impairs the subjects ability to hear the position of sound sources. (Ie,
a speaker
mounted in front of the subject, he or she would hear coming from the
ceiling.)
(See nature-neuroscience, september 1998, Hofman, van Riswick, van
Opstal, 
see also http://www.mbfys.kun.nl/mbfys/people/paul/pubs.htm for a pdf
version.)

The reason this works, is that the external ear works as an acoustical
filter.
The characteristics of the filter depend on the incident direction of
the sound, 
and the brain uses the information to reconstruct the position of a
sound source
from the sound on the eardrum. Change the acoustics, and the brain gets
confused
about the position of the sound.

Changing the acoustics of the external ear, would certainly also change
the way in 
which we hear certain partials. We could selectively amplify certain
paritals,
by mounting a specific configruation of putty in the ear. However, one
would 
have to try several putty forms and see what effect it has on which
partials.

As for the props you use, that I don't understand, because there is no 
resonance anymore then

regards,

Jos.

___________________________________________________________
J.G.A. van Riswick, Eindhoven University of Technology,
Eindhoven, The Netherlands. mailto://j.g.a.v.riswick@tue.nl
mailto://josvanr@xs4all.nl http://www.dse.nl/~josvanr


Ken Jankura wrote:
> 
> List,
> I think I may have hit on something to help us all do our work better and
> more efficiently. Recently I was tuning and having a little trouble hearing
> the partials I wanted to hear. Though I use an Accu-tuner now, I learned to
> tune aurally and I always check as I tune to try to improve on the machine.
> Well, I was tuning the high treble and noticed that I could hear the 2nd
> partial, the 2:1 octave, better when I opened my mouth. Try it, you'll
> definitely notice a difference. If you open your mouth just a little it
> seems like the second partial just gets isolated a little more than normal.
> There must be something of a synergistic effect in using your eustachian
> tube as a resonator chamber. So I then went the next step, and opened my
> mouth as wide as I could and I noticed that the 6th partial just rang out
> as clear as a bell. It was really simple to hear and tune the bass this
> way, except that my jaw got tired. So what I've come up with is a series of
> "Partial Props" that I carry in my toolcase, four of them, to help me hear
> what I want to hear. They range in size from 3/4 inch to 2-1/4 inches,
> pieces of dowel rod, turned from beautiful tropical hardwoods, with teeth
> protecting rubber caps, for different ranges of the piano. Thank goodness I
> don't have to use that 2-1/4 inch one very often, that's for an 8:4 octave,
> but the 1-7/8 inch works great for a 6:3, the 1-5/32 inch for a 4:2, and
> the 3/4 inch for the 2:1. Customers do look at me a little funny, but I
> just take the prop out of my mouth and explain that it's for the good of
> the piano. I was hoping to go into business manufacturing these, until I
> realized that each person is going to have to find their own best
> dimensions, their own 'sweet spot', if you will, to get the best effect. So
> don't let your eustachian tube just sit there, make it work for you! My
> tunings have never gone so smoothly or so quickly.
> Ken Jankura
> 
> 

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