At 01:20 PM 7/04/02 -0700, you wrote:
>Dear Reg and Vocalisters:
>>Sally I understand your problem with inertance but while I try
>>and see it from where you do, I have a problem with giving it
>>a very serious impact on the cords as long as the tuning of
>>the tract is in sympathy with the current operation of the cords.
>>
>>Different story if they are not tuned.
From Lloyd....
>COMMENT: May I refer you to an excellent discussion of inertance and
>its effects on the vocal folds in Titze's book "Principles of Voice
>Production" His research indicates strongly that the inertia of the
>air column in BOTH the supra and sub glottal area provides a load on
>the vocal folds that is necessary for continuation of vocal folds
>oscillation. His book also does a good job of explaining Fourier
>analysis of sound waves and its use in voice research.
Lloyd I give in to your greater knowledge but I have a problem with the
term 'inertance". This seems to be a term more recent than my
education, still my objection, or confusion is centred on the dynamic
fact that there should be TWO types of inertance. As I mentioned in
the earlier piece, there are TWO sources of the 90degree shift in a
resonant system. This also applies to ALL parts of the upper system.
They used to be called "inductive reactance" and " capacitive reactance"
in a resonant system. Each of these is a "reactive" impedance. BUT,
their vector addition results in an over-all cancellation leaving only the
REAL resistance and a very mysterious one called dynamic resistance.
To refer to inertance of the vocal tract, leaves something missing.
As I said before, an oscillating mechanical system has two characteristics,
MASS and SPRING TENSION. Each of these has a direct relationship
with an electrical resonant system. I know this is so, because I have
used this fact to tune a mechanical system where the MASS is fixed
so that all I have left to adjust is the spring tension. This spring tension
equates with the "capacitance" in an LC circuit. (No not Low Carb:), but
L for inductance and C for Capacitance.
Perhaps I need to hear a clear definition of "inertance"
The reflected load onto the cords would be very important, but the fact
remains that whatever the value of the "inertance " reflected, if the upper
area ...as a final result, is tuned, then it will not be an inertance,
but a resistance, which implies a non-reactive characteristic...that is,
the inertance of the effective MASS of the air column, is EXACTLY
balanced by the SPRINGNESS of the upper walls, (or something,)
to yield a final outcome of exact resonance with the oscillating folds.
>>Such a condition is just what we all seek with varying
>>degrees of success.
>
>COMMENT: "A dynamic resistance." But "Non-reactive"? If the load
>is "totally resistive" aerodynamically it WILL affect the oscillation
>of the vocal folds. Such may not be true of electrical processes
>such as a "generator" with source "impedance" that is in reality a
>dynamic "resistance", but it is true of aerodynamic processes. I
>have nothing to indicate that what applies to one field will apply,
>wholesale, to another. As mentioned above, the inertance of the
>vocal tract is a necessary source of resistance energy to maintain
>the continuous oscillation of the vocal folds; vocal fold elasticity
>and the action of the Bernoulli Principle, of themselves, is not
>sufficient.
(me) Lloyd this is still a mechanical system and while I certainly
agree that the air flow is the driving force behind the oscillation, the
real problems seem to me to lie in the understanding of the upper
area. Another difference is that all the displacements are "positive"
that means there are no "negative" excursions of the air flow but
that is not a problem for Fourier analyis for example, where there
is provision for a DC or contant value.
Just as the average value of a sine wave is ZERO, this fails to
tell the whole story. Whether we deal with electron flow and
voltage or, air flow and pressure difference. the resulting power
is (EI cos theta) where E is voltage I is current and cos theta
is the cosine of the phase difference between the two quantities.
For power (energy) a positive value for one, times a positive
value for the other still yeield a BIG + in the power stakes but
also, a MINUS value, times a MINUS, also yields a BIG + in
power. ONLY if cos theta is 90 degrees, do we have a big
problem. (Of course even 45 degrees is not too good either.)
Which brings me back to the problem of the "type" of the
load reflected by the column onto the cords. (cos90" = 0 )
I neglected to point out that those crico thingies represent
the springs in the folds. :)
Regards Reg.
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