Re: [Harp-L]Comb test

[MundHarp@xxxxxxx]

Vern...
 I used to think... Wood comb = warm   metal comb  =  bright...
Was it in 1997 or 1998 that I was participant with you at SPAH   in 
Detroit, in the comb test? You know, that proved to me... The audience  can not 
tell the difference!
No more, no less!
John Whiteboy Walden,
Just now in bonnie Scotland.
 
 
In a message dated 10/28/2012 8:39:32 P.M. GMT Standard Time,  
jevern@xxxxxxx writes:

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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