Re: [Harp-L] SPAH 2010 Comb Test: a thought experiment (long)

[Michelle LeFree <mlefree@xxxxxxxxxxxxxxxxxxxxxx>]

 joe leone writes:

<huge clippage>
> What I was trying to say here was that while the sound may SOUND the 
> same to listeners, the FEEL of the sound may FEEL different to the 
> player. It could be the vibrations?

<Even more clippage>

Good, good, good vibrations. Interesting you should mention them Joey, 
because I have been thinking about them a lot lately. I think this 
phenomenon of harps vibrating differently in a player's hands and mouth 
can shed light on our ongoing discussion about the comb experiment. 
Here's why:

I play wood, plastic and metal combed diatonics (different temperaments 
for different genres, mostly). I don't ~think~, I ~know~ that when I 
play my Suzuki Promasters -- that have aluminum alloy combs -- I can 
without question ~feel~ those harps vibrate in my hands and mouth to a 
significantly greater degree than I can feel vibrations in harps with 
combs made of the other materials, wood or plastic. I think there is 
information in the fact that different harps vibrate differently in the 
hands and mouth of the player and that such information bears directly 
upon the questions asked in the comb experiment.

I'm not a real acoustical scientist by any means and I don't even play 
one on TV, but I have solved many acoustical boundary value problems 
(differential and partial differential equations). I can say from this 
experience that materials have characteristic acoustical impedances just 
as they have characteristic electrical impedances (resistance, 
capacitance and inductance). Materials with low acoustical impedance 
transmit acoustical vibrational energy where materials with high 
acoustical impedance absorb it. Sound wave reflections occur at 
boundaries between materials of different acoustical impedances (much as 
in physical optics). The higher this difference in acoustical 
impedances, the greater the amount of reflection. (As examples, foam 
rubber would have high acoustical impedance, where steel would have low 
acoustical impedance. That's why you see that egg-crate foam lining 
recording studio walls.)

With this technical underpinning, here is a little thought experiment. 
Another way of looking at this physical phenomenon of acoustical 
reflection is to understand that if one material is absorbing acoustical 
energy and another is reflecting it, the amplitude (loudness) of the 
reflected sound waves will be greater in some way with the reflecting 
material than the absorbing one. Makes sense, right? So one might then 
ask how two harps, one with its comb made of a "reflecting" material and 
the other of an "absorbing" material (unnamed in this experiment) would 
feel in one's hands? Could it be that the one that vibrates more 
strongly in the hand would have a comb that is absorbing less acoustical 
energy and vice versa? I think so.

I posit that the harp with a comb material that doesn't absorb 
acoustical energy transmits more vibrational energy to the player's 
hands and mouth than a harp with a comb that ~does~ absorb acoustical 
energy (and likely to a listener as well but let's stick to analyzing 
what the player feels). Hard to argue with that. If you feel one harp 
vibrating in your hands and mouth to a noticeably greater extent than 
you can feel when playing another harp, it is intuitively obvious that 
the lesser vibrating harp has done ~something~ with that acoustical 
energy that you ~aren't~ feeling transmitted to your hands and mouth. 
Yes, folks, I am saying that that harmonica somehow ~absorbed~ that 
energy. And since the other components (reeds, reed plates, cover 
plates) are the same as the other harp it must be the comb that did the 
absorbing.

I hope you are with me so far if you are still reading this. What I am 
saying here is that, from a purely theoretical view, based on the 
different levels of vibration a player feels in their hands and mouth I 
believe I have informally proven that the sound exiting two harps, one 
with a sound absorbing comb and the other with a sound reflecting comb 
~must~ be different in some way. I further contend that the inherent 
differences in the acoustic properties of comb materials must cause some 
sort of a filtering effect (whether or not frequency-dependent) in which 
the frequency spectrum of sound emitting from harmonicas with different 
comb materials are different in ways that are characteristic of the comb 
materials.

I fully realize that this idea is in conflict with Vern's long-standing 
position. His argument that the wavelength of the sound a harmonica 
produces are much longer than the dimensions of a reed chamber and 
therefore the comb material can have no effect on the transmitted sound 
seems to hold water. Yet, how can this clear difference in how harps 
vibrate in the player's hands and mouth ~not~ bear some sort of a 
relationship with the sound emitted out the back of the harp?

These are the musings I think about when I try to reconcile my 
real-world experience playing and listening to harmonicas with my 
admittedly limited experience with acoustical dynamics in air. [My 
experience is almost all to do with studying sound waves in a (mostly) 
water-equivalent material (i.e. diagnostic ultrasound of the human 
body).] I would like it very much if Vern or anyone else can explain to 
me how one harp that feels like it nearly comes alive in your hands 
could ~not~ produce a different emitted sound compared to another with 
which the body of the instrument vibrates noticeably less. I'm not even 
saying at this point just how the two sounds might differ, but that they 
must differ somehow (though I have my ideas). (BTW, no one will convince 
me that those aluminum-combed harps don't vibrate much more in my hands 
than a wood or plastic-combed instrument so don't even try.)

Now whether these differences in the sounds emitted by a harp with a 
more reflecting comb material and one with less reflecting material are 
detectable by the human ear or not I don't know (I personally ~think~ 
that they are). But my gut tells me that spectral analysis of the 
recorded sounds from those different combs will show some kind of 
differences. I'm looking forward to learning when the results of the 
analysis of those spectra will become available, and what kind(s) of 
analyses were applied.

At least that's the way I see it.   I'm sure Vern (and probably others) 
will "feel" differently. ;-)

Michelle