Re: [Harp-L] widening out/opening up the backs of harps

[Rick Dempster <rickdempster33@xxxxxxxxx>]

I agree, no difference worth noticing; but what, for example, Joe Spiers
does makes the plates stronger,
so my 'pocket' harp does much better with this particular mod.
RD

On 9 March 2016 at 08:33, Vern <jevern@xxxxxxx> wrote:

> Widening of the backs of harmonicas will have little effect on the sound
> for several reasons.
>
> Diffraction is the tendency of sound waves to widen out when passing
> through an opening smaller than the wavelength.  This means that the shape
> and size of the back opening will not affect the direction of the sound.
> See
> http://www.ck12.org/user:a2VsbGV5dEB1c2QyMDQubmV0/book/Waves-and-their-Interactions-with-Matter/section/1.1/
>
> The area of the back opening is huge with respect to the area of the reed
> slot.  As a consequence almost all of the pressure drop occurs across the
> slot. This means that constriction of air flow by the back opening is
> minuscule.
>
> The logarithmic response of the human ear makes small differences in
> loudness imperceptible.
>
> I have covered more than half of the back opening of a harmonica and have
> not been able to measure any difference in loudness on a meter.
>
> Bottom lineâRobert is correct, flaring the back opening is a waste of
> effort.
>
> Vern
>
>
> > On Mar 7, 2016, at 10:09 AM, Robert Hale <robert@xxxxxxxxxxxxxx> wrote:
> >
> > On Mon, Mar 7, 2016 at 9:45 AM, Peter Beck <kpfbeck@xxxxxxxxx> wrote:
> >
> >> widened out the backs of a bunch of Special 20s
> >
> >
> > âI haven't found the result to be worth the work to open the backs of
> harp
> > covers.
> > I consider gapping, embossing, and arcing more worthwhile than flared
> > covers.
> >
> > NEAR
> > There are some variations of sound heard by the player in close proximity
> > to the reeds. Since it is a personal experience, one may choose to pursue
> > the modification.
> >
> > FAR
> > I don't think the audience, and most players, can distinguish open to
> > closed back harp on stage.
> >
> > To evaluate what a microphone picks up, and delivers to an audience,
> either
> > live thru the PA or recorded medium, we would need to test only ONE
> > variable: the open to closed back of ONE model harp.Other variables among
> > harps are reed composition / design, comb, choice of mic, and EQ in the
> > chain. Again, if the A/B difference is significant to the player it can
> be
> > done.
> >
> > So I place the topic down the list of important activities. Best use of
> my
> > time is practice and performance.
> >
> > Robert Hale
> > Serious Honkage in Arizona
> > youtube.com/DUKEofWAIL
> > DUKEofWAIL.com
>
>
>
>