[Harp-L] Re: Are different overtones available by changing reed shape?

Robert Coble asks:

Has anyone experimented with changing the basic reed shape in
order to change the set of overtones which are produced, or to
emphasize specific overtones, thereby changing the timbre of
the harmonica?

This has been tried, though perhaps not with the harmonica. I had remembered a patent with odd shaped reeds, and when I didn't find it I asked Pat Missin, who had already put some on a webpage (of course):

http://www.patmissin.com/history/kratzenstein.html

Here we can see star-shaped, circular and other odd reed forms. Of course, the basic reed outline is different, but this does indicate it has been tried.

I realize that there are serious complications for trying to create
this type of thing for mass production. I'm just curious as to the
effect (if any) that could be made on the overtones produced.

It would be interesting to see what odd shapes and such do. However, the biggest changes to the tone of the free-reed I've encountered come from two sources. First, attaching a large, specifically tuned and designed resonant chamber to the reed. This is similar to using specific hand-cupping shapes or playing into a cup, in that the resonant chamber enhances and dampens specific frequencies--a filtering effect. The Vocalion and the related Aeolian Orchestrelle used this idea to create some truly impressive free-reed organs which were able to get much closer to the sound of flue pipes and the like than the standard reed-organ. The Second method was that used by most American suction reed-organ manufacturers in the 19th century: twisting the reeds. Here, the tongues were distorted and twisted along their long axis. Not enough to cause problems with the sides of the hole, but enough to alter the tone and speech characteristics of the free-reed, usually to make it milder and present more fundamental. This would probably not be feasible with a harmonica, as the twisting leads to a massive change in the efficiency of the reed which is easily compensated in a reed-organ by large bellows and a constant supply of wind, but probably less so in a mouth-blown instrument.

Or, perhaps the set of overtones is fixed by the very nature of
a free reed, regardless of the reed shape/design?

To a large degree it is. That is why most accordions, concertinae, melodicas and harmonicas sound so similar. You do get more variation by the means described above with reed-organs, but they are still (with perhaps the Vocalion exception on certain of it's stops) easily recognized as being in the free-reed family. I've worked on 32' pitch free-reeds with gigantic tongues and huge wooden resonators, and in the end, it's a big harmonica:).

1. Try a reed with the reed tip rounded instead of square. The
reed plate would also have to be rounded to match.

The patent listed above has the entirety of the reed as round, but certainly a rounded tip would be easy enough to make. Fill in the end of the slot with an epoxy (I believe Siegfried Naruhn has posted on how to do this to shorten slots) and then take an oversized reed. Cut the reed end into a rounded shape, and then scribe away the infill of the slot to match the new shape. I doubt the difference would be all that much, but I'd be interested in the results.

2. Try a reed which is tapered (wide at the reed heel, relatively
narrow at the reed tip), with a reed plate and chamber shaped
similarly.

Very common. Many (most?) accordion reeds are made this way, as I believe are melodica reeds. I know of at least two harmonicas that have tapered reeds, the Suzuki Alto and Soprano Singles. I have an Alto Single, and it does have a bit more bite and projection than similarly ranged harmonicas--crisp is a good word for the tone. But how much of that is due to other factors of reed-scaling and the like than the taper I can't say. I can compare it to other isolated reed all-blow instruments in the same range, so there is a difference, especially in projection (the Alto Single is loud), but as I said, I can't say how much is the reed's shape and how much is other factors. In any event, the difference is not huge--it still sounds like a harmonica. I think for most of these things we're talking about small variations on a theme, rather than radical alterations.

3. Try planing the sides of the reed slot so that there is no "lip"
for the reed edge to cut against. Think reed mounted to the
chamber rather than to a reed plate sitting on the chamber,
with just enough clearance between reed side and chamber wall
to allow free movement, but with a small "lip" ONLY at the reed
tip to produce sound waves. Would that produce only a
fundamental with no overtones?

Not exactly sure what you're describing, but is it similar to this patent (also from Pat Missin, of course):

US 518957

If you mean that the chamber and the walls of the reed-slot are one and the same, I'm not sure how well that would work. As you say, all the air would be at the tip of the reed, but what would that really do to how the reed functions. I've never seen something where there wasn't some space on the sides of the reed. This would probably be easy enough to try and make yourself--simply cut a comb the exact width of a slot, using the slot itself as your guide, and then mount the reed on that original slot. You don't need to make an entire comb for the experiment--just one chamber to fit one reed would let you know a lot about the basic idea.

5. Try a reed with a rounded "blob" (or other irregular shape)
at the reed tip. A variation is to use 2 or more lobes on the tip.

I doubt that blob shape is all that important. If the tip itself is odd shaped (as in the first patent and your fourth question) that's another issue, but a blob on top of an otherwise normal reed probably won't have too great an effect, at least before you get to such irregularities that the reed simply won't speak. I've seen all sorts of odd blobs on beating reeds, and while these are very different, it seems that the weight and placement of such was the most important factor, not the shape of the blob. I would think the same may be true for free-reeds. But blobs would certainly be easy to experiment with.

6. Try a very small pinhole (or a series of pinholes) in the middle
of the reed which would leak a very small amount of air through
it. I suspect this might change the available attack, but not
change the overtones.

This has also been tried:

US 572286


I've been told by someone who tried this (and incidentally supplied all of the patent references in this post) that it made no difference whatsoever. Maybe in larger, higher-pressure reeds there might be some effect, but it seems not with harmonicas.

7. Try mounting the mouthpiece at right angles to the reed plate,
so that the air goes directly at the reed tip at a 90 degree angle,
rather than sliding along the reed almost in the same plane as
the reed.

No difference whatsoever, IMO. I say this because you can try this easily enough yourself. Simply take a reed-plate and press it directly to your lips. The sound is loud because it's perfectly airtight, but other than that there is no significant tonal alteration. I think in any system where a comb and the like was involved rather than being pressed directly against the lips, the airtightness level will be about the same as with a standard harmonica and thus the loudness factor eliminated. Especially in a duel-reed-cell design.

Thanks for the intriguing (at least to me) post. These ideas may have already come up once or twice as the patents show, but it always helps to get them discussed again and maybe encourage people to try them. While the patents do exist, I'm not sure anyone alive has ever heard the results, so who knows--there could be significant things lurking there. Certainly I've not really seen something like your #3 even in patents.




 ()()    JR "Bulldogge" Ross
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