Re: [Harp-L] harmonicas are not guitars

[Vern <jevern@xxxxxxx>]

On Oct 29, 2012, at 6:55 AM, Mike Fugazzi wrote:

> Coverplates have more of a direct impact on "tone", IME.  If you have a few 
> different models from a company, you can try this out yourself.  For 
> example, take a Marine Band and try it with SP20 covers.  Then compare the 
> two to a harp without any covers on i

What we hear is very subjective. I cannot believe my own tests because I cannot avoid confirmation bias, (hearing what I expect to hear). You and I can compare the same harps/covers and will probably arrive at different conclusions about the effect of covers on tone/loudness.  Only a blind test involving a group of people can make a correct assessment.  That is why the effectiveness of drugs is tested with double-blind comparisons.  People who know that they are receiving the experimental drug will claim to feel better more than people who know they are receiving the placebo. You can't let them know and you can't even let the people administering the drug know (double-blind.)  

At SPAH97, listeners could not tell the difference between two CX12s, one with stock ABS and the other with bare brass covers.

When thinking about the effects of combs and covers, diffraction is often overlooked.  It says that an obstacle which is small with respect to the wavelength will have little effect on the wave.  Think of a post in the surf.  The waves pass right by without attenuation or change in direction.  A sea wall which is several wavelengths long can reflect the waves.  A long, porous rock mole which is several wavelengths long can attenuate the waves. 

 The wavelength of middle-C is about 4 feet and the harmonica is about 4 inches long. The features that distinguish one cover from another are of the order of a fraction of an inch.  It follows that one should not expect any appreciable effect arising from differences in comb and cover details.

Perception of small differences of loudness is hindered by the logarithmic response of the human ear.  It takes a very large change in sound pressure to be perceptible.

Then there is masking. See http://en.wikipedia.org/wiki/Sound_masking.  Consider the harmonica to be two sources of sound. The louder is the sound that comes to your ear directly from the slot and does not pass through any solid part of the harmonica.  The weaker source passes through the covers and comb and is emanated to the air by the small surfaces of the harp.  Think of a plucked reed.  At to near the same frequency, it requires a very large change in the weaker sound to be perceptible.  I posit that subtle changes in the materials and shape of the comb or covers are incapable of producing such changes.

I have nothing good to say about leaks.  However, if they are small with respect to the leakage through the opening reed of a diatonic or through the slide of a chromatic, they can be small enough without being perfect.  Considering these unavoidable leaks in most harps, going to extremes would be like weatherstripping the windows in a house with no front door.

Vern