First, I wanted to go back to this part of Ken Deifik's original post on cover shapes:
"Beyond shape, here goes an actual materials question: do different metals or coatings on the covers change anything? "
I believe John Walden mentioned it already, but there was a test done (I can't remember if it was at SPAH or not) where brass and plastic covers for a CX-12 were used to see if there was a difference listeners could hear between the two. There was not. Not an ideal test by any means, but much like the comb materials tests, it indicates that cover material is probably unimportant in tonal issues.
However, Smokey Joe answered:
"Absolutely. Some things will deaden sound, some will enhance it. I put sticky foam tape inside my Herings to cut down the pinchiness. A coat of sizing and then application of gold leaf will deaden the sound. Chrome plating seems to be brighter than cadmium or nickel.
The key word here is "seems". I suggest that since you expected a change due to these differences, you heard one. Everyone does this, it's simply part of being human--if we expect a difference, we are likely to find it whether it exists or not. The idea that the covers "absorb" or "resonate" sound due to their materials is not one I think holds up to further scrutiny. For one thing, the actual area of the cover is very small. It would need to be much, much bigger to have an effect due to the material or covering of that material. Remember, the sound of the harmonica is all-but entirely composed of that massive column of air moving through the instrument, and so for a material to have a significant effect on that body it would need to be similarly large.
Mark Lavoie writes:
"Every thing on the harmonica makes a difference in tone! Covers, Wood combs, how the comb is sealed, how big the chambers are"
Perhaps, but is that difference significant is the question. If humans can't hear the difference, then does it matter. And so far, the few tests that have been attempted have indicated that humans can't hear the difference. Moreover, I've yet to see any theory as to why especially comb material but also cover material would have any effect on the harmonica at all (even an insignificant one) which stood up to even the slightest bit of logical examination.
Vern writes:
"There is nothing about the acoustics of the harmonica that suggests that the covers play any role in the generation of the sound. The covers define the shape of the sound passage from the reeds to your ear. They might conceivably affect the coupling of the sound to the outside air as does the bell of a horn. They might have a slight effect on loudness but not tone."
I'd agree completely. Though I think Vern is being a bit conservative--the cover can block and direct the sound in certain ways. Thus the side-vents of a Marine Band. What is happening here, though, is that the cover is being used to alter and effect the resonant chamber which one makes with the hands while playing. This is a body into which the instrument is blown and which can have an effect on both tone and volume--as here the resonant body (your hands) is large enough to have an effect (though, again, I doubt materials would matter much--metal hands would not sound, "crisper" I'd venture). You are essentially filtering out certain harmonics and letting others through, and also changing the amplitude of the sound--thus both timbre and volume can be changed by the use of your hands. But, this is the hands, and not the inert cover which is doing this, though some designs such as the MB may make certain hand effects easier or even doable which can't be done with others.
This can be seen in an extreme example--the Suzuki Pipe Humming. Here, significant effects in volume and timbre can be achieved by controlling the openings of the tube into which the harmonica is inserted. But, perhaps the most significant thing about the Pipe Humming is that if you don't use this feature and just play the instrument with the sides of the pipe open, it sounds no different from other harps such as the Suzuki Promaster. So, even a radical example like this only has an effect if used in a way which creates a larger resonant chamber (via your hands) to significantly alter the way the sound gets out into the room.
What this indicates to me is that cover shape has a limited effect and would need to be both larger and probably variable in size and shape--ie, the covers would need to essentially mimic what is done with the hands and create something like a Helmholtz resonator to have a significant effect.
Smokey Joe again:
"Aaaah, I don't know about that Vern. I placed 1" x 1/16" (25mm x 1.5 mm) sticky foam tape inside the covers of my Hering 64 and it sure made a difference...to ME. What do you think it was? Was it the change in vibrations going to my hands? Or maybe the change in vibrations going to my skull?"
As above, I suspect that the difference was in your mind. The mind is an amazingly powerful thing, and the psychological factor should never be underestimated. Thus the need for blind tests and the elimination of human variables.
Tim Moyer asks:
"Rather than trying to prove that it's all an illusion, why not just allow the illusions to guide performers to bring their audience to subjectivity? "
I for one have always advocated that if the player believes that the instrument is superior because of any factor it will probably improve their performance--whether that factor is real or imaginary. However, there's a big difference between accepting either the psychological factor in performance or the choice of people to believe as they wish (though don't expect me to not comment when people start proselytizing) and advocating for ignorance--I quite dislike the latter.
()() JR "Bulldogge" Ross () () `----'
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