----- Original Message -----
From: "Zombor Kovacs" <zrkovacs@xxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Friday, April 20, 2007 1:03 PM
Subject: [Harp-L] comb dimensions
What about comb depth? Or maybe we call it width. I am
talking about the length of the chamber, not the
height. How does that affect the sound?
I think that the dimensions are important only because they affect the
volume of the reed chamber. The chamber and your embouchure can form a
Helmholtz resonator whose frequency is a function of its internal volume and
the area of an orifice opening to the outside. My experience is that
chamber shape doesn't affect sound very much but I would not say that it has
no effect at all. The manufacturers, like Douglas Tate, who put ramps in
the high pitched reed chambers obviously believed that it makes a
difference.
I attached a large syringe to a single chamber that could be placed over any
reed of a loose redplate. I blew air in through a plastic tube through the
end of the chamber where it usually enters. The setting of the plunger in
the syringe had major effects on the response of the reed. At some settings
the reed would not sound at all and at others it responded enthusiastically.
In this case, I think the syringe acts more like the player's embouchure
than it does as variations in chamber size. It demonstrated to me the
importance of embouchure and/or chamber volumes. It may be that chamber
volume has a small effect because it is small with respect to the player's
embouchure.
When tuning, I often "kiss" the loose reedplate to sound a reed without
putting it back on the comb. Here there is no chamber at all but the opening
in my mouth. I find that the very high-pitched reeds respond best when I
hold my mouth as though there were a golf ball in it. The very low pitched
reeds respond best when I put my tongue close to my lips and minimize the
open volume in my mouth. The middle pitches will respond well to almost any
embouchure. This demonstrates that the volume of the chamber is an
important variable. However, it is puzzling and the opposite of what I had
predicted. Go figure!
Incidentally, the fact that I can "kiss" the reedplate and produce a note
that sounds exactly the same as it does when the plate is in the harmonica
convinces me that the comb material plays no important role in sound
generation and propagation. You can produce a note with a wind-instrument
reed or mouthpiece from a trumpet or clarinet but it sounds nothing like
playing the whole instrument.
Vern
Visit my harmonica website www.Hands-Free-Chromatic.7p.com