[Harp-L] Re: Reed gapping questions

[Vern <jevern@xxxxxxx>]

I posit that a reed has optimum response when it spends about half of each cycle in the slot.  The following explanation still holds if the optimum time-in-slot is more or less than 50%.

In addition to its vibrational displacement, a reed has an average displacement in response to static breath pressure.  IF you are a hard blower, the reed needs to start farther away from the plate so that the average deflection places it at the position for optimum time in the slot…..and vice versa.

Because there must be some flow through the slot at startup to begin oscillation, the gap cannot be zero. IF the gap is so large that the reed never reaches the slot, oscillation will not begin.  

In two-reed draw-note bending, the lower-pitched opening blow reed  sees reverse static pressure, pushing it away from the slot.   Thus the optimum gap will be lower than it would be in the normal closing mode. 

In an attempt to dispel the mystique of gapping involving the secret knowledge of experts and trial-and-error methods, I have made several tools for measuring gaps and have made many measurements of gaps on real reeds.  I believe that if you can accurately measure, record, and set gaps, you can achieve similar reed performance in different harps without special expertise or trial and error. That said, the effect of gap can be obscured by the effect on resonance of the player's embouchure.

Many feel that this explanation fails to consider other (unexplained) variables.  I welcome alternative explanations for discussion.

Placing a tube from your manometer in your mouth while you play would give you a fairly accurate measure of breath pressure.  This reasonably assumes negligible pressure drop across the mouthpiece. Bear in mind that the tube will affect your embouchure.  Another way would be to connect the manometer to a tiny hole in the back of the comb. I made most of my pressure measurements with the manometer connected to a pressure table with bare reed plates. I would be interested in the pressures that you measure. 

Vern
 
 
On Sep 15, 2013, at 8:00 AM, Aongus MacCana <amaccana@xxxxxxxxxx> wrote:

> I liked your informative post on this topic. From what I have gleaned from this list and elsewhere, it seems that large gaps are for hard players and small gaps for more gentle players. From what I understand this is only a matter of response – in whether the reed decides to vibrate or not and that it does not have much or anything to do with tone. What I find interesting is that this is the first time I have seen anyone suggest an objective physical measurement of soft and hard blowing:  “0.5 ins. Water gauge is gentle playing and 10 -12 ins. Water gauge is going fairly hard”.
> I made a simple U Tube manometer from transparent fuel tubing years ago for the purpose of balancing twin carburettors on VW and Porsche engines. I am beginning to wonder whether I might be able to stick the end of the tube into my mouth ahead of the tin sandwich and establish where I stand in the “hard blowing stakes”
> Beannachtai
> Aongus Mac Cana
>