Re: [Harp-L] reed plate thickness
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- Subject: Re: [Harp-L] reed plate thickness
- From: Winslow Yerxa <winslowyerxa@xxxxxxxxx>
- Date: Fri, 14 Nov 2008 10:28:30 -0800 (PST)
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- Reply-to: winslowyerxa@xxxxxxxxx
The shortened reed life associated with thicker reedplates is due to the wider swing of the reed to pass through the reedplate to the other size while vibrating. Wider swing = bigger (louder) vibration and also more stress, hence shorter reed life. A brass comb would not have this effect because it does not thicken the slot.
The engineering types onlist could comment with greater authority than I can on the following, but I suspect that even with a brass comb (i.e., one as hard as the reedplate instead of softer like wood or plastic), it would still be possible to over-torque a screw fastening a thinner object (reedplate) to a thicker one (comb). As I red it, the key in David Payne's assertion that screw torque is more evenly distributed on a thicker reedplate is not the relative hardness of the reedplate and comb, but the thickness of the reedplate itself.
Moving the slot edge farther away from the reed to overcome surface tension (if that's what's going on) would just make the reed/slot combination leaky - and you'd still have surface tension. The 'bad old days" of Hohner reeds (roughly 19080s/90s) was largely a result of such leaky slot tolerances - the reeds were fine but the slot edges were just too far away, resulting in harps that sucked too much air while delivering weak volume and dull tone. I recently worked with such an old reedplate that was otherwise virgin, and even aggressive embossing only partially mitigated the lack of response and dull tone - evidently the slot tolerances were really relaxed on that harp.
Some recent posts seem to suggest that the optimal combination is to have a slot tolerance that is not so tight that you can't emboss - that rolling the slot edge downward and inward from a slightly greater distance is better than simply having the edge of the slot as close as possible with a 90 degree angle.
Embossing the slot opposite the reed (i.e. on the other side of the reedplate from the reed)? It hasn't been widely discussed, and I don't recqall anyone having reported results from it. The surface where the reed/slot/air interaction is strongest is at the reed itself, though, so i suspect that this is where the greatest difference will be found. There is, however, a danger that pressing the slot edge inward on the opposite side will create the opportunity for the reed to hit the overhang as it passes through the slot due to torsional vibration. Just as with embossing on the reed side, you'd have to be careful not to over-emboss.
Chamfering or otherwise widening the slot opposite the reed is another possibility, though my suspicion is that it would effectively make the reedplate thinner (because the air is channeled narrowly to a reduced depth). Whether or not this would simply result in the same tonal and response results as a thinner reedplate (generally reported as faster/brighter), or whether it would introduce some other more nuanced result (or no discernible result at all) would be an interesting set of experiments for someone to carry out . . .
Author, Harmonica For Dummies ISBN 978-0-470-33729-5
--- On Thu, 11/13/08, Harvey Berman <cscharp@xxxxxxxxxxxxx> wrote:
From: Harvey Berman <cscharp@xxxxxxxxxxxxx>
Subject: [Harp-L] reed plate thickness
Date: Thursday, November 13, 2008, 10:53 AM
If thicker, or double reed plates are used, which causes the reeds to swing
further, therby increasing volume, and shortening reed life, and it does this
because the thicker reedplates distributes the screw more evenly, holding the
reedplate flatter, then what happens when you bolt regular reedplates to a brass
comb? It would seem that the whole assembly suddenly becomes one large
reedplate, with reeds mounted on each end.
Does the volume go up, and reed life go down because of the brass comb?
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