Re: [Harp-L] How does bending actually work? (the physics)

[Arthur Jennings <timeistight@xxxxxxxxx>]

>From http://www.klausrohwer.de/privat/hobbies/muha/muhapubl/bending.htm:
 Jetzt zur Physik: man hat hier ein System von drei (und nicht etwa nur
zwei) schwingungsfähigen Gebilden vorliegen. Es handelt sich um die beiden
beteiligten Stimmzungen und die Luftsäule im Mund-Rachen-Raum. Letztere
befindet sich beim Mundharmonikaspielen idealerweise in Resonanz mit der
Schwingung der gerade gespielten Stimmzunge; in diesem Fall ist der Ton
besonders laut und schön. Wenn man jetzt die Mund-Rachen-Stellung verändert,
so dass die Resonanzfrequenz tiefer wird, so macht die Stimmzunge der
Mundharmonika diese Veränderung mit, d. h. sie schwingt nicht weiter auf
ihrer eigenen Resonanzfrequenz, sondern vollführt eine erzwungene Schwingung
auf der Resonanzfrequenz *des Systems* aus Stimmzunge(n) und Luftsäule.
Nähert sich diese Frequenz der Resonanzfrequenz der zweiten Stimmzunge (im
vorliegenden Beispiel der Blaszunge), so gerät auch diese in (erzwungene)
Schwingungen. Beim tiefsten Bendington schwingt dann die Blaszunge alleine,
obwohl der Luftstrom eigentlich in die "falsche" Richtung weist.

Translated by Google to:
 Now for the physics: we have here a system of three (which is not available
as only two) oscillatory structures. These are the two parties reeds and the
air column in the mouth and throat area. The latter is the harmonica playing
ideally in resonance with the vibration of the reed being played, in which
case the sound is very loud and beautiful. If one now changes the position
of the mouth and throat, so that the resonant frequency is lower, the reed
of the harmonica makes these adjustments, ie, they no longer vibrates at its
own resonant frequency, but performs a forced oscillation at the resonant
frequency *of the system* of reed (s) and air column. In this frequency
approaches the resonant frequency of the second reed (in this example, the
Blaszunge), it also falls into this forced () oscillations. At the deepest
Bendington then swings the Blaszunge alone, although the airflow actually
goes in the "wrong" direction.



On Fri, Mar 19, 2010 at 1:28 PM, Tom Klingl <tom.klingl@xxxxxxxxxx> wrote:

> Klaus Rohwer is a physiscyst and he gives a very detailed scientific
> explanation
> http://www.klausrohwer.de/privat/hobbies/muha/muhapubl/muhaphys.htm. He
> also
> uses a numerical model with a finite elements software to show what is
> (theoretically) happening to a reed. The videoclips are quite impressing
> http://www.klausrohwer.de/privat/hobbies/muha/muhapubl/moden.htm. He also
> was able to film the process real-time
> http://www.klausrohwer.de/privat/hobbies/muha/muhapubl/strobo.htm
>
> However you have to be able to read German to get full coverage. Dave Payne
> might get a kick out of it...
>
> Tom
>
> -----Original Message-----
> From: Arthur Jennings [mailto:timeistight@xxxxxxxxx]
> Sent: Friday, March 19, 2010 7:11 PM
> To: michael rubin
> Cc: harp-l
> Subject: Re: [Harp-L] How does bending actually work? (the physics)
>
>
> I am not a physicist, but here's what I think is happening:
>
> There are three resonances interacting in an unvalved bend: the draw reed,
> the blow reed and your mouth. As you lower the resonant frequency of your
> mouth cavity, you force the draw reed to vibrate at a lower rate. (This is
> what is happening on a single-reed bend on a valved harp.) As the pitch
> gets
> lower, it gets closer to the resonant frequency of the blow reed, which
> excites the reed and causes it to vibrate.
>
> You can observe this sympathetic vibration effect on a string instrument.
> If
> you play an 'A' or the low 'E' string of a guitar and watch closely, you
> can
> see the open 'A' string vibrate along with it. In fact, if you stop the
> note
> on the sixth string you'll continue to hear it from the still vibrating
> fifth.
>
> On Fri, Mar 19, 2010 at 10:02 AM, michael rubin <
> michaelrubinharmonica@xxxxxxxxx> wrote:
>
> > I have often explained to my students that when draw bending, what we
> > think of as the blow reed takes over the vibration and does the bend
> > sound.  I take the cover plates off of a harp, I bend, I put my finger
> > on the draw reed, stopping the reed's vibration and the bend continues
> > to sound with vibration on the blow reed's part while the draw reed
> > has stopped.  This has satisifed many students, but today I have met
> > my match.
> >
> > How does the blow reed take over?  How does bending fool the blow reed
> > into vibrating quicker and producing a higher pitch?  What does the
> > symathetic vibration of the draw reed have to do with it? Thanks,
> > Michael Rubin
> > Michaelrubinharmonica.com
> >
>
>
>
> --
> Arthur Jennings
> http://www.timeistight.com
>
>
>


-- 
Arthur Jennings
http://www.timeistight.com