Re: Bends: physics and physical

["Tim Moyer" <wmharps@xxxxxxxxx>]

paul wrote:
> So while I spent those hours trying to evoke a bend, I would ponder 
> what the heck is going on that causes a bend. I understand the 
> sympathetic resonanance of the opposing reed causes the bend, but 
> why are some notes bent, and others bent to varying degrees? 

Thanks to Pat Missin for pointing to the research papers that have 
been published on the subject of how bends are achieved.  I think 
some of the misconceptions held by players have to do with the 
term "bend" referring to the alteration of pitch of the note.  
Calling the process a "bend" implies either that the angle of attack 
of the airflow has been altered or bent, or that the reed is somehow 
physically changed or bent in the process.  

The fact that you can achieve a bend through a soda straw indicates 
that angle of airflow isn't a factor.  Many players also feel that 
because they typically achieve their first bends at high air 
pressures means that it take a lot of air to "bend" the reed 
physically, but this is also not a good assumption.  With practice, 
bends can be attained at very low volume (amplitude).  

It really is all about resonance and sympathetic vibration.  The 
player changes the size and shape of the resonnant cavity of the 
mouth which results in a change in pitch of the vibrating reed.  In 
the case of a two-reed chamber, this can cause the opposing reed to 
vibrate sympathetically, which allows the pitch to be changed 
further.  The amount that the pitch can be changed is a function of 
the natural pitch of the sympathetic reed.  In holes which allow only 
a slight amount of pitch change (say, hole 5), the two reeds are 
tuned only a semitone apart (allowing less than a semitone of pitch 
change).  In holes in which a large amount of pitch change is 
possible (like hole 3) the reeds are tuned four semitones apart 
(allowing about 3 semitones of pitch change).  

If any of this is to be helpful when learning to control bends, 
perhaps it is in the visualization of the size and shape of the mouth 
cavity while practicing.  Try bending at lower and lower air 
pressures and you'll find that it really is a matter of finesse over 
force.  

- -tim

Tim Moyer
Working Man's Harps
http://www.workingmansharps.com/