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From: WVE~ol.com
Date: Fri, 4 Oct 1996 21:25:45 -0400
Subject: Re: CX-12 & materials

In a message dated 96-10-04 06:04:02 EDT, m.carley writes:

>They (cover plates) aren't completely covered in player-flesh (how
>big are most people's hands?) and the fact that they're
>held on three edges doesn't mean anything. In fact, one
>of the paths of vibration transmission is probably through
>the attachment points.
>
For any vibrating part, it is more important where you touch it than how much
area is covered. Touch it near a loop of vibration and you kill the
vibration almost entirely. Touch it near a node and there is almost no
effect. The points of attachment of a vibrating part are very important to
the modes in which it will vibrate. Every place that you attach it removes
possible modes of vibration (because loops cannot exist there) and stiffens
it, raising the frequency range of excitation to which it will respond.
Holding the harp as do most players, you touch the covers in enough places to
prevent most of the natural modes of vibration.

Another factor is at work. The covers touch the reedplates all along the
front edge of the harp. If the cover tried to vibrate very much, the plate
would rattle/slap against the reedplate. The collisions would very quickly
and thoroughly absorb any energy of vibration. Jet engine compressor blades
have projections that touch similar projections on their neighbors. The same
mechanism that I describe above supresses damaging vibration of the blades.

I think that you make an unwarranted assumption that the covers are excited
by vibrations of the parts to which they are attached. All of the parts of
the harmonica (except for the reeds) are small, stiff, and acoustically dead,
not only of themselves but much more so when assembled into a harp. With
your fingernail, tap on a guitar and hear the response of an instrument that
has truly acoustically active parts. Tap on a harmonica clutched in your
hand in playing position and you hear almost nothing.

In a harmonica, the air passages are where the action is, not only inside the
instrument but also in the embouchure and in the cavity formed by the
player's hands. Even the reeds themselves (because of their tiny surface
area) radiate hardly any sound directly. It is the siren-like throttling of
the flowing air by the reeds that creates what you hear. Thus the shape of
the parts that form the air passages can be important to the tone but the
materials of which they are made has almost no influence.

I wish it were otherwise. I have invested a lot of money and time in
developing an ability to make reeds and combs of various materials with the
idea that I could create magical sounds with exotic materials. Sadly, it
just doesn't work that way.

Maybe I missed an opportunity. Maybe I should be building and selling
harmonicas of exotic materials because players seem to be so easily convinced
of their efficacy.

Vern