RE: [Harp-L] Note Bending Science

["Aongus Mac Cana" <amaccana@xxxxxxxxxx>]

Hi Vern,
Some "expert" on the list said some time ago that chamfering - scarcely
possible or measurable as you remark (due to how thin the reeds are)
definitely did something for volurme.
If you started chamfering the reed plate it would seem to undo any benefit
of embossing or swaging the plate to reduce reed clearance.
What the heck lets just try to play the darn thing!
Beannachtaí
Aongus

-----Original Message-----
From: Vern [mailto:jevern@xxxxxxx] 
Sent: 15 February 2011 22:42
To: Aongus Mac Cana
Cc: harp-l@xxxxxxxxxx
Subject: Re: [Harp-L] Note Bending Science


Because the reeds are so thin (about .012" at the tip if there is a slug on
a low-pitched reed and much thinner than that for the other reeds, hardly
any rounding is possible. 

More rounding is possible on the .040" thick reedplate.  It seems plausible
that rounding the edges of the slot might reduce the loudness of high
overtones by making the closing of the flow passage less sudden as the reed
swings through the slot.  

In order to verify this speculation, one would need to take audio
spectrograms before and after altering the slots.   
To determine if it is perceptible to listeners, a carefully designed "blind"
comparison of sounds from rounded and unrounded slots would have to be
arranged.

I expect that the spectrograms might show slight differences but listeners
would be unable to perceive any difference.....but I could be wrong.

Because the pressure ratio and consequently the velocity and Reynolds number
are low, viscous effects predominate over inertia effects in the flow.  This
reduces the effect of sharp edges and roughness on total flow. In any case,
I doubt that the player or the sound of the harp would be affected by a
slight increase in total flow....but I could be wrong.


Vern


On Feb 14, 2011, at 8:23 AM, Aongus Mac Cana wrote:


As a retired mechanical engineer, I am predisposed to take an interest in
"airflow around the vibrating harmonica reed" and "the effect of the
resonant frequency of the oral chamber on frequency of the played reed" 
However both of these topics are best suited to PhD theses and are not going
to do me a darned bit of good in learning to bend. At my age I am in a bit
of a hurry! 
Another related topic which cropped up on the forum before, is the advantage
- or otherwise of chamfering reeds i.e. taking the sharp edges off them.
Some of the 'experts' are convinced that this affects volume and tone. It
seems plausible to me that this process would  increase airflow around the
reed like the Hot Rodder's beloved "Three Angle Valve Job"
Beannachtai
Aongus Mac Cana