Re: [Harp-L] very simple questions

[Zombor Kovacs <zrkovacs@xxxxxxxxx>]

Thanks for the answers to everybody. I hope I will
hear more on the topic. BUT, right after I sent my
mail to the list, I have got closer to the solution.
Thanks for the articles, I have read them already more
or less, but I have not found detailed description of
the flow phenomena around the reeds and in the vocal
tract. But let me share with you what I know so far.

In my description I have only been talking about hole
number 1 in fact as subject of investigation. Thus I
have been referring the blow reed as upper reed and
the draw reed as lower reed because of their location
in the chamber.

I have figured out that one must investigate the
behaviour of individual reeds (which may not be a
worldwide invention :-). It is not unknown, that there
are 2 reeds in each chamber. It has also been
discovered, that we can make any of the reeds sound
individually, by DRAWING the air or by BLOWING the air
(so in both ways). 

Drawing the air normally the lower reed will sound OR
if we drawbend the note DOWN, the upper reed sounds.
Blowing the air normally the upper reed will sound OR
if we do "overblowing", the lower reed starts
vibrating only. Now we made all two reeds sound in
both ways (blow and draw). 

If we block the upper reedslot thus eliminating the
upper reed and draw on the lower reed we can still
bend it DOWN, like in a valved bend. This means that
the frequency of vibration gets CLOSER to that of the
upper reed's. Bending this way, we can approach the
frequency of the upper reeds natural frequency. 

Now if we eliminate the lower reed (block the lower
reedslot) and draw on the upper one, we can drawbend
it UP, so its vibrating frequency approaches that of
the lower reeds natural frequency. Conclusion: drawing
the reeds, they can be bent "TOWARDS" each other. 

If we remove the blocking and get back both reeds into
the game, I PRESUME that the same happens. 


Draw bending

As I start lowering the pitch of the lower reed (draw
reed), somehow (donno how), I start making the upper
reed (blow reed) also sound but at a lower pitch than
its natural frequency, and with low amplitude (quiet).
As I continue bending, the amplitude of the lower reed
(draw reed) decreases, but frequency increases. It
becomes gradually more quiet but higher pitched. 

Meanwhile the amplitude of the upper reed increases
(louder), but frequency decreases (lower pitch). At
one point they arrive at the same frequency and
probably more or less same amplitude and both sound.
After this, the upper reed gradually takes over. In
the end only the upper reed sounds. 
This whole thing is possible, because the reeds can be
bent "towards" each other frequency wise. 

Blow bending

With a blocked upper reed and blowing the lower one
(overblow), the pitch can be highered. With a blocked
lower reed and blowing on the upper one, the pitch can
be lowered. This means that the originally lower upper
(blow) reed?s pitch can be even more LOWERED thus
getting AWAY from the frequency of the lower reed
(which is the draw reed). So the transition we get by
draw bending (reeds bending towards each other) is not
possible because the reeds are bending ?away? from
each other. 
But if we use a lower pitched draw reed from a lower
key harp, it will start bending in the same
?direction?, thus bending towards the upper reed and
the smooth transition will be possible by blow
bending.

What I dont know: How does bending work in a single
reed bend? (like in a valved harp, or with the other
reed blocked). 
Lets take hole number 1 in BLOW mode:

The reeds are bent ?away? from each other (abrupt
change from blow to overblow)
Draw reed blocked: The blow reed can be bent DOWN.
What is the reason that the pitch is lowered?
Blow reed blocked: the draw reed can be bent UP
(overbend). What is the reason that the pitch is
highered?


DRAW mode:

Reeds can be bent towards each other (smooth
transition, traditional bending)
Draw reed blocked: The blow reed can be bent UP.
Again, what is the reason that the pitch is highered?
Blow reed blocked: The draw reed can be bent DOWN. And
what is the reason that the pitch is lowered?

I am curious about physical reasons, if there is
anybody who can answer me. I have also no idea what is
happening inside the vocal tract during bending. I can
do it, but I dont know what is happening to the flow
or resonating conditions (in case these cause the
bending). 

cheers
Zombor


--- Vern Smith <jevern@xxxxxxx> wrote:

> 
> ----- Original Message ----- 
> From: "Zombor Kovacs" <zrkovacs@xxxxxxxxx>
> To: <harp-l@xxxxxxxxxx>
> Sent: Wednesday, August 03, 2005 12:26 PM
> Subject: [Harp-L] very simple questions
> 
> 
> >I have 2 very simple questions to those interested
> and
> > involved in harp physics.
> 
> The questions may be simple but the answers are not!
> 
> I am very interested in harp physics but do not
> pretend to have all of the 
> answers about bending.  I once wrote an FEA-type
> computer program that could 
> predict the frequency of a reed (within a wholetone)
> from the properties of 
> the metal and the variable-thickness profile. I have
> a videotape by Dr. 
> Bahnson at the university of Pittsburgh ( A friend
> of Antaki's) on the 
> "Physiology of Bending".
> 
> > There must be a reason, why bending can only be
> done
> > "towards" the lower sounding reed.
> 
> In a bend, both reeds are vibrating at a frequency
> between their natural 
> frequencies.  They are linked together by the fact
> that they both feel the 
> same chamber air pressure.  You cannot expect the
> frequency of the 
> combination to be above that of the higher reed or
> below that of the lower 
> reed. Certainly if you linked them mechanically, you
> would expect an 
> intermediate frequency.
> 
> In a harmonica chamber, the Reynolds number is very
> low because the chamber 
> cross section is small, the pressure ratio of the
> flowing air is very small, 
> and velocities are low.  With very low inertia
> effects, pressure gradients 
> within the chamber are most likely negligible.
> Wavelengths at the 
> frequencies at which bending is done are very long
> with respect to the 
> chamber dimensions. A flute sounding middle C
> excites a resonant column of 
> air about 30 inches long.  The middle-C chamber in a
> harp is less than one 
> inch.
> 
> The steady-state static pressure of the player's
> breath in a chamber varies 
> from about 0.5 inches of water to about 15 inches of
> water with respect to 
> atmospheric pressure.  .
> 
> I believe that the lower pitches are easier to bend
> because the reeds are 
> more limber and have a greater area to be acted on
> by the air pressure.
> 
> The bend is also influenced by the player's
> embouchure.  The player most 
> likely forms a Helmholtz-type resonator with the
> volume of his mouth and 
> throat as the "jug" and the area of his lips on the
> mouthpiece as the 
> orifice.   When the player applies this resonator to
> the playing reed he 
> "pulls" its frequency down so that it approaches
> that of the lower (opening) 
> reed and starts it vibrating.  As it begins to
> influence the air pressure by 
> opening and closing its slot, the pressure
> variations in the chamber is 
> affected by both reeds.
> 
> Vern
> 
>



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