Re: Re: [Harp-L] Re: Something with full-length covers!

["Vern Smith" <jevern@xxxxxxx>]

Mouth comfort is a valid advantage of long covers.

For the following reasons, I doubt that the difference in 
the area of the opening in the back can perceptibly affect 
the sound of the harp.

If a larger opening were louder and better, then the much 
larger openings of chromatics would be perceptibly louder 
and better.  I doubt that any of us would agree that such is 
the case.  Most diatonic players would argue the reverse.

The % difference in the rear openings between full-length 
and tabbed covers is small...say 10%.  Only for the sake of 
argument, assume that the sound energy emitted by the harp 
is  proportional to the area.  Then a 10% area difference 
(or an energy ratio of .9) would produce only an 
imperceptible  0.5  db difference in sound level.
( 10 x log(.9) = 0.5 db approximately)

Most of the intuitive reasoning about covers assumes that 
they have a major directional effect on the sound, but this 
is not so.

I placed a sound meter about a foot away from the harp in 
front of my face and then 90 degrees to one side.  Blowing 
at the same loudness to the best of my ability, there was at 
most a 2 db difference in loudness.  This would be a better 
test if the harp were blown by a machine and the meter were 
read by someone besides me but it satisfied me that the harp 
was behaving as the acoustic theory predicts.  From an 
opening (under the covers) much smaller than a wavelength, 
the sound waves propagate equally in all directions.

I posit that the effect of differences in cover shape will 
be imperceptible, especially when the harp is hand-cupped.

Vern










Vern



----- Original Message ----- 
From: "Winslow Yerxa" <winslowyerxa@xxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Wednesday, April 08, 2009 11:38 AM
Subject: Re: Re: [Harp-L] Re: Something with full-length 
covers!


> >From replies so far, what I'm getting is mouth comfort 
> >factor as the attraction of full-length covers.

> Now I know that diatonic players do place value on opening 
> out the back of harmonica covers. But I've never heard 
> discussion about whether restricting the width of the 
> covers to the reed area (as in Marine Band, Lee Oskar, 
> Special 20, etc) as opposed to running the length of the 
> harp (Golden Melody, Meisterklasse, Suzuki Firebreath, 
> Seydel Favorite, etc.) had any perceived benefit.
> Winslow
>
> Winslow Yerxa