Re: [Harp-L] comb design/structure



Many of the puzzling design features of plastic combs are there to prevent warping as the injection-molded comb cools. The plastic is squirted into the steel mold as a hot liquid. Then it starts to cool and shrink. As it comes from the mold, it is solid but still hot. IF one part of the harp cools and shrinks faster than another part, warping can result. If you tried to injection-mold a comb the shape of a wooden comb, it would be a crooked mess when it finally cooled down.

Thick and thin cross sections cause warping. In a harp, the thin sections would be in the middle of the harp and the thick sections would be at the ends. The thin sections cool and shrink faster than the thick sections. The ends and the back are hollowed out with grooves and openings of various sizes to help them cool as fast as the partitions between reed chambers.

The bar you refer to was no doubt put there as a brace to prevent warping.

Because the air passages in the reed chambers are very large with respect to the slot that is mostly blocked by the reed, you won't notice any differences related to air flow under the bars..

And of course we all know that the material of a comb does not perceptibly affect the sound of the harp. ;o)

Vern
Visit my harmonica website www.Hands-Free-Chromatic.7p.com

----- Original Message ----- From: "Marc Molino" <mmolino54@xxxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Thursday, July 05, 2007 6:41 AM
Subject: [Harp-L] comb design/structure



If you look into the hole of a diatonic harp, why do some models have a bar running horizontal across the middle of the comb (e.g. Golden Melodies) and some have none (e.g., Marine Bands)? Is this a manufacturing issues w/ plastics vs. wood? Are there plastic combs that do not have such a bar? Are there wood combs that do have this bar? It does not seem to have any impact upon the sound, but it would seem like it should affect airflow somehow...

Curious,
Marc Molino

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