Re: [Harp-L]Comb test

[Vern <jevern@xxxxxxx>]

We will be condemned for using Harp-l bandwidth for this discussion.  

On Oct 27, 2012, at 7:08 PM, David Payne wrote:

> The problem is, Vern, I believe you're mostly right. But we could do brass vs. wood next time I am able to get to a Spah where we could do it and I'd like to draw in my other four most-trusted ears as well, if they'd be willing (Jason Ricci and Wally Peterman).

My wager is that nobody can differentiate among comb materials under controlled coditions. You are welcome to include as many participants as you choose.  If anyone succeeds, I lose.   Bear in mind that in in three previous tests, everyone anticipated being able to do it but no one who actually participated and put their perceptions on paper could.  Participants included many well-known harmonica virtuosos.  

>  You could give the $1,000 to Young Harmonica Allstars International or keep it, whatever. I, on the other hand, do not have $1,000 to put up, nor am I really concerned about that money. I only want to better understand how the harmonica works.

That also is my goal. I admit that if I thought anyone could do it, I wouldn't risk $1000. The wager is a way to dramatize my confidence and the lack of confidence of those who disagree. You can assemble a syndicate of believers to raise the $1000.

> I have thought for years about this and I have been in varying degrees on both sides of this fence. I was positive that comb material had no effect on tone, Vern had convinced me of this. I was positive until the 2010 SPAH test. The brass comb seemed so vibrant to me and I could usually hear it. I was sitting back far enough where I couldn't see what was what and I made it a point not to look. What I heard made me rethink everything.

>  I've done quite a few experiments. Some of those experiments indicate Vern is right. Some of those experiments indicate that Vern is not. 
> My current hypothesis is that we have all been wrong to some degree and that Vern has been more right than most, but not entirely right.

I have also done my own experiments.  However, hearing is very subjective. I have a skeptical bias and could not trust my own perceptions.  Thus it was necessary to get other listeners & players involved.
>  
> This is mostly for those following along. I would never insult Vern's intelligence, which I respect by going into some of these elementary details, and I'm sure Vern will think I'm full of it anyway, lol.:

This has nothing to do with my intelligence or profound lack thereof.  I would have difficulty defining the word. Consider only my arguments, acoustical theory, and the evidence from the tests actually conducted.   
>  
> The most basic thing that affects tone is the reed itself and the resonant chamber.

I disagree. The most basic thing is the non-linear area of the flow passage through the slot as the reed opens and closes it.  This is very much the same for all reeds. The responsiveness of the reeds can vary with their stiffness. Two reeds of the same pitch can have different stiffness and respond differently to the player.  This will be more apparent to the player than to the listener.  Think Hering and Hohner.  

> How it is profiled - the varying thicknesses along its length...
This can affect fatigue life, but not tone.  

> - and how the air flows to the reed. I was fortunate enough to soak up a lot of Harrison Harmonicas' work on studying the affect of air flow to the reed on tone.

> The resonant chamber, of course, is the human innards.
I agree. I think of the reeds as substitutes for the human larynx.

>  Here is an explanation of air flow: 
> http://www.elkriverharmonicas.com/harp_school/1890s

I believe that holes in  the covers an inch or more from the reed have a negligible effect.  I can place a reedplate to my lips and blow a harmonica tone without the presence of comb or covers. The air flow pattern must be very different for draw and blow notes but there is not a perceptible difference in the sound.  Anyone can play a C and the adjacent B# on a chromatic to verify this.  Because the pressure ratio is very close to 1, the velocity of the air is low and the passage is small.  Thus the Reynolds number is small, and the viscosity effects predominate over the inertial effects.  That means that the reed doesn't know what the air is doing an inch away.  Holes in the cover may affect what the player hears.

 Most people think of a difference in tones as they would think of the tonal properties of materials on instruments such as guitars or mandolins. The problem being that those woods serve as resonant things. Combs don't work that way. 

I agree.
> 
> Jacob Hohner had a theory back in the 1890s that coverplate resonance had an affect on tone. That was the whole point of the Mouse Ear Marine Band, to lift the coverplates up from the reedplate and minimize contact with the reedplate, so the coverplate would be more free to vibrate. The sound from a guitar, for instance, comes from the vibrating top, not the "sound hole." the sound hole is actually there to relieve air pressure inside - even medieval builders understood that. When I wrote the page linked to above, I thought Richard Seydel's side-vent air flow concept was more valid than Jacob Hohner's coverplate resonance concept, but since have changed my mind to believe they are both equally-valid concepts. Jacob Hohner's vibrating coverplate concept isn't very well accepted, the argument being how is this possible when your hands are on the coverplate. How can it vibrate.

Hohner's countryman, Helmholtz, developed a good understanding of resonance which is described in his1877 book.  He also Chapter three describes the operation of soundboards. 
>  
> So I did a couple of experiments. First experiment I thought would totally debunk Jacob Hohner. I tried playing a single note, then laying my index finger across the coverplate. I expected to hear nothing, but I was shocked to hear a definite change in tone. As my finger was placed on the top coverplate (as I blew a note), there was a noticeable decrease in treble overtones. So, my next question was if the finger is on the coverplate, is there still sound vibration traveling in the coverplate? 

I conducted essentially the same experiment.  I concluded that any differences arose from the effect of the finger on the path from the reeds to the players ear.  Our perceptions agreed with our biases.  That is why blind comparisons are necessary.

>    I sought to answer this on my kitchen table, which is fairly small. I placed my ear on table and then rapped my knuckles on the other side and listened to how that sounded. Then, I laid my body across the table (I'm 6 feet two inches tall, 240 pounds). This seemed to me like a good scale test. I did the same thing while laying across the table and noticed how the rapping sounded. It was not dampened.

Assuming that the cover responds to the excitation of sound in the air, I posit that the effect is minuscule and imperceptible.
>  
> So, I thought, if the sound can still travel through the material when a weight is pressed upon it, can it still have an affect on tone - then I realized that you can only cover less than 50 % of a coverplates' surface. The inside surface is always uncovered and free.

In order to have an effect on tone, it must drastically affect the spectrum of the sound...attenuating certain frequencies more than others.  Then it must emanate the altered frequencies loud enough to not be masked (http://en.wikipedia.org/wiki/Masking_threshold) by the main harmonica sound that comes directly from the slot to your ear without passing through any part of the harmonica. I posit that this doesn't happen.

Vern

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