Re: [Harp-L] triple vs quadruple reed harps

[Zombor Kovacs <zrkovacs@xxxxxxxxx>]

Rick, what do you call "suitable environment"? 

I agree with Vern that deflection stresses a reed, which certainly does but this issue is rather complicated.
The reed works in a medium, with certain density. Has anybody measured if breath pressure causes any significant change in the density of air? Reeds restrict airflow and behind a blowreed there must be a pressure buildup, while behind a drawreed there should be a pressure drop. Sound waves propagate at different speed in media with different densities resulting in altered pitch which is not something that influences reedlife directly, but media density could influence it as higher density air has more mass. More mass has more inertia, and more inertia could cause higher deflection and lead to quicker fatigue failure. This is again just a theory and might not have an effect, but it would be interesting to have some results on it. 
Air density also comes into play during resonation phenomena which is quite a factor in harmonica physics. I think we do not know too much about resonance phenomenons inside the harmonica although Jim Antaki has some serious articles on related topics. A theory of mine is that our lungs and oral cavities coupled with the harmonica act as Helmholtz resonators, or even multiple coupled Helmholz resonators. What happens inside exactly however, I don't know.

And just another reason came to my mind why the XB40 could be louder. It is not the same, what material the resonator is made of. Whether it is hard plastic, or soft human tissue. An XB40 has a relatively large additional chamber volume compared to a normal diatonic. If you remove the XB40 coverplates, it is still loud so it is not just coverplates which do this. So here we have an extra large resonator coupled between the reed and our mouth. I wonder if you confirm this (sorry if it has already been discussed and I missed it).

Zombor



________________________________
 From: Rick Epping <rickepping@xxxxxxxxx>
To: Vern <jevern@xxxxxxx> 
Cc: harp-l@xxxxxxxxxx 
Sent: Sunday, September 16, 2012 12:38 AM
Subject: Re: [Harp-L] triple vs quadruple reed harps
 
Hi Vern,

I agree that it's deflection that stresses a reed.  I believe that the
greatest degree of deflection occurs at the moment when a reed is brought
into play from a rest position, by the initial burst of air that the player
gives it in order to make it respond.  The more suitable the reed's
environment, the less breath pressure will be required to make it respond
and the less deflection will occur during the initial attack.  An example
of this can be found in a comparison of the high notes of the 270 Super
Chromonica with the old comb, with those with new comb, in which the space
in the reed cells has been reduced.  It's curious that, while a reed
responds better in the presence of an opposing reed with a lower frequency,
it also responds better in a reed cell with a higher resonant frequency
than its own natural frequency.  Reducing the depth of the highest cells in
the 270 comb has raised their resonant frequencies to above the natural
frequencies of their reeds, with the effect that these reeds require less
breath pressure to respond than with the old comb.  Similarly, the
improvement in response given to a reed by the presence of a lower-pitched
opposing reed results in less breath pressure being required to make it
respond, and therefore less deflection and less stress at the moment of
attack.

Best regards,
Rick

On Sat, Sep 15, 2012 at 9:15 PM, Vern <jevern@xxxxxxx> wrote:

>
> On Sep 15, 2012, at 9:20 AM, Rick Epping wrote:
>
> "..................................  I tend to believe that playing a
>
> reed in an environment which allows it to oscillate closest to its natural,
> or plucked frequency, is less likely to stress it than in other, less than
> optimal environments......................."
>
>
> Based on the mechanics of materials, here's a counter-argument:
>
> Amplitude/deflection (shorter radius of curvature) is the only thing that
> stresses a reed.
> The greatest amplitude/deflection will likely occur at the natural
> (plucked) frequency.
> It follows that the amplitude and stress will be less in "less than
> optimal environments."
>
> You may be incorrectly projecting the player's stress onto the reed. The
> reed doesn't care if the player's eyes are bulging, his embouchure is
> convoluted, and he is red in the face with bending effort.
>
> Vern
>
>
>