Re: [Harp-L] Re: THE COMB DEBATE REVISITED: SPAH Test

[Vern <jevern@xxxxxxx>]

On Jul 13, 2010, at 9:57 PM, JohnnieHarp wrote:

> Coverplate design and mods is one that comes to mind given current
> claims made by customizers and manufactures as to volume increases,
> etc, resulting from different coverplate forms (Suzuki Manji for
> instance) ... personally, I have my doubts in the validity of these
> claims based on my experiences ...

There are acoustic principles to support your skepticism and experience.

Diffraction:
Through openings of less than a wavelength, sound spreads equally in all directions along circular wave-fronts.  Think of a pebble tossed in a pond. Because it is much shorter than a wavelength, the shape of a harmonica cover will not affect the direction of the sound.

Logarithmic human hearing:
The human ear has a logarithmic response...and a good thing that is!  The same ear that can hear the buzzing of a mosquito or the wind whispering through the pines is not destroyed by a clap of thunder or the output of a loud harmonica amp.  However, it means that a few holes or a slight change in shape of a cover that affect the emanated sound energy by a small amount will be imperceptible.  Besides that, the covers are usually touched, enclosed,  and their possible effect negated by a hand-cup.

Cover design might/could have very minor effects on harmonica sound level,  but in real-world situations, the differences will be imperceptible.  The function of covers is to keep your hands off of the reeds.

The cover materials have no effect at all.  Siegfried Nahrun made brass CX12 covers that sounded no different from black plastic ones.  The notion that a shiny gold coating on CX12 covers will affect the sound is laughable.

I have blocked off half of the cover opening of a diatonic with a slab of metal thicker than the cover without changing the reading on my sound-level meter.  This means that bending the cover to increase the opening is futile.

Vern