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

[Vern <jevern@xxxxxxx>]

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