[Harp-L] Comb construction/material

[David Payne <dave@xxxxxxxxxxxxxxxxxxxxxx>]

 I'm calling it comb construction, because this is not necessarily a question of materials, it's construction/materials combined, with the construction being more important than the materials.

I was at the SPAH comb test at the Minneapolis SPAH in 2010. It showed that tonal differences between materials weren't so obvious that even really good players could ID specific materials by sound. It it also demonstrated something very significant to me, the player is in no better condition to hear changes in tone than anybody else. As I remember, there were three types of comb materials involved, all were traditional tin sandwich design, with a set of reedplates being clamped to each of the three combs, except one, metal. As I sat in the audience, I tried to guess them too. Between wood and plastic, I was as wrong as everybody else. However, there was one comb that would "ZING!" - in my ears anyway - when it was played, the metal one. The vast majority of times when the metal comb was played, I could identify it correctly. There were a couple of times when the brass comb sounded like the others, I think that might have been some small variable in
 the clamping (although I have no idea truly what happened) but the majority of times it sounded vastly different. 
I should note, I don't play metal combs. Brass and aluminum are dissimilar metals and when I touch my tongue onto the harmonica, I get that taste like when you lick the poles of a 9 volt battery (that's how we tested 'em when I was a kid). When the metal comb (I think it was actually brass) popped up in that Spah test, it almost always hit me like "wow!"
 While just before it started, it didn't look like he was taking it seriously, I did really trust Chris Michalek's ear. I knew the other testers and knew they were fantastic players, wonderful people, but I didn't know their ears. So I was paying a lot of attention to Chris. I think he was about as wrong as often as anybody else on guessing the materials. One interesting thing I noted: Chris wasn't noticing the brass comb as it popped up like I was and I honestly believe he had a better ear than mine. I was sitting there, shocked, thinking "how is nobody noticing this sweet brass comb? How is Chris not picking up on this?" That left me wondering if the player is actually in a WORSE position to notice tonal changes than somebody farther away from the instrument. 

I've spent the last two years mulling this over. I've come to a conclusion that it isn't the tonal properties of a material that account for differences, it's the way in which vibrations travel across the harmonica, altered by variables in both material and construction.
I think it's obvious that the vast majority of tone comes from the player's acoustic resonance and the reed itself. The things I'm describing below would account for only a small change in that tone and I am talking ONLY about diatonics here - as that is all I have seriously experimented with.
A vibrating surface does emit sound energy. There's no more obvious place to look than a guitar. Now guitars have soundholes. Those aren't places for sound to come out, it's for air to come out. Early guitars, in fact, didn't have an open hole there at all, but usually some fancy wood mesh, intricately carved. The sound comes off the surface of the wood on the guitar's top. Same with violins, whose F hole slits are very small and you think "how does sound come out of this!?!" It doesn't really. It's primarily a vent for air pressure changes. When a string is played, that top vibrates in and out. If there is nowhere for the air to go, it's like trying to shut a car door with the windows up. But crack and window and it shuts easily. Yes, harmonicas are not guitars or fiddles. My point is simply - vibrating surfaces emit sound energy.

That's where the likenesses end, because there is nothing acoustically resonant about a harmonica. It's too way too small. Comb material has nothing to do with acoustic resonance. Maybe, on some theoretical level, it's resonant at some overtone, but it's a stretch and chamber sizes are pretty standard. 

But there are other forces at work. On the occasional harmonica, you play a high-frequency note on the upper end, something can make a lower reed vibrate to the point it emits sound. The fact that a reed can be blown on one reedplate and there's enough energy transferred through the harmonica to make a reed vibrate on the other plate, indicates that there is a significant amount of such force at play inside a harmonica. It's interesting that it seems to happen usually happens to a low reed when a high note is played. Cathal wrote me off list and said when the covers were removed, the ghost reed vibration stopped. Same for the ones I've had. I would think that points to when you remove the coverplates, you change that mechanical resonance in some way that makes the forces at work do something different, in these cases, not make that other reed vibrate. 
If such vibrations are transferred through the harmonica and cause the other side to vibrate, then how the other side vibrates should alter, even if to a miniscule degree, the tone. We know that a vibrating surface emits sounds. Thus if it vibrates, it must sound. 
This concept of vibrating harmonica surfaces altering tone isn't something I invented, exploration of this concept was the revolution of the 1890s that gave us our modern diatonic. Two people were working on this at the same time, Richard Seydel Sr. and Jacob Hohner. I can't find a copy of Seydel's patent, but he seems to understand air flow in tonal changes, with four vents to direct air from the corners - I think it was a better design (the original Bandmaster), but I don't have his patent to get that glimpse of what was going on inside his mind. Hohner was thinking only only of acoustic vibration, the sound energy going from the reedplate down, not coming up from the reedplate itself. I mention this because, 120 years ago, these guys at least basically understood the concept of vibrations in the instrument changing the tone. When you sit down and think about this for the modern player cupping the harmonica tightly, it doesn't quite make as much sense,
 because you would think the hand would dampen vibration. What is significant here is that Jacob Hohner noticed that when you lifted the coverplates up from the reedplate, it changed the tone. The result was the 1896 Mouse Ear Marine Band.
Like I mentioned with the hand dampening the vibration on the coverplates, you would think it would even be more dampier for a reedplate, which is bolted to a comb. But sound energy can travel through different mediums.  Take the table I'm typing on right now. It's a heavy table. It might as well be bolted to the floor. If somebody raps their knuckles on one end and I put my ear down on the other, I can hear that knock coming up from the table. Even if it were bolted to the floor, like a reedplate to a comb, the table would still transmit the sound energy of that knock. Even if I had people laying on it (to recreate the dampening effect of hands on coverplates), that sound energy from that knock would still be transmitted from one end of the table to the other. The table itself, despite the fact it cannot - same is true for a reedplate - move in a way we can see, it still transmits sound vibrations.
If you look at the total surface area of a harmonica, there is a significant amount of surfaces where vibrations can reach the air as sound energy. The reedplates, plus inside and outside surfaces of the coverplates to varying degrees, I suppose, based on what you are doing. 
I think these instances of cross-harmonica reed soundings show us that a significant amount of energy is transmitted via vibrations through materials. Despite the fact the our hands are on them, the coverplates appear to play some, perhaps even a significant one, role in this transfer or energy. When Cathal took the coverplates off, that ghost reed vibration stopped. I've had the same findings with the ones I've come across. 
I've never been able to notice a tonal difference between the 1847 Silver and 1847 Classic, despite the fact one is wood and one is plastic. They are the same harmonica, only one has a comb made of maple, the other a plastic designed to have the same "give" as wood - that little crushability that allows the comb to push out against the reedplate when the screws are tightened - there are little air spaces inside the plastic to mimic wood. So between these two, there appear to be no difference in the tone of these two vastly different materials, but they would seem to conduct vibrations very similarly. 
But I do hear a difference with the Session steel, which has a recessed reedplate on a plastic comb with a lot of hollow chambers. 
So, my contention is it is not the material itself, but how the material allows the transmission of this energy from one side to the other that accounts for tonal differences. Even, then, the reed itself and the player contribute so much to that tone, you have to be listening specifically for it to notice it. 
If I ever get back to another SPAH or something, I would like to try a tone test. I suppose this could even be done with e-mailing recordings back and forth. Each sample would have an extended note played on each of two harmonicas set up identically and only one question. "are the combs different or the same." The plastic would be a recessed reedplate Seydel Session Steel and the wood would be an 1847 classic, both with 1847 classic coverplates (like the 1847 Silver Plus used to be). I'd want the three ears I trust most for the test, mine, Jason Ricci's and Wally Peterman's.  Then repeat it with other ears and see what trends pop up in the data.

Retiring to a safe corner and ducking,

David
www.elkriverharmonicas.com