RE: Subject: Re: [Harp-L] comb thickness (was material)

[Winslow Yerxa <winslowyerxa@xxxxxxxxx>]

There are two aspects to comb thickness:

- player comfort

- effect of reed chamber geometry on reed behavior 

The standard diatonic thickness seems to be the most comfortable for
players. This may be due to what diatonic players are already used to -
many different types of harmonica have many different overall
thicknesses in the mouth - chromatics, bass harmonicas, Auto-Valve
style octave harps, and single reed diatonics, among others. But people
who play primarily the single reed diatonic seem to be physically
uncomfortable with anything significantly thicker.

When I first started desiging the Discrete Comb, I took two wood-combed
Marine Bands, removed the top cover and reedplate from one and the
bottom cover and reedplate from the other. I then sanded the exposed
comb top of one and bottom of the other to half-thickess, and glued
them together with a thin sheet of plastic in between. 

The resulting harmonica was within a millimeter of standard thickness
for a diatonic, but the reed chambers were only half as tall and half
the total volume. The harp was comfortable enough in the mouth but
would only respond to a very light breath attack and would not produce
much volume.

As I developed milled combs with discrete upper and lower chambers, I
started at nearly double the thickness of a standard comb, then
progressively thinned the comb. The optimal thicness turned out to be
abourt 1.5 times the standard thickness. Any thicker and no gain was
realized; any thinner and response and volume suffered. Chamber volume
was increased by carving more volume out of the walls of the "teeth" of
the comb, which were structurally supported by the horizontal separator
between upper and lower chambers.

Of course this is in a case where upper and lower (blow and draw) reeds
are physically isolated from one another and expected to interact in
the same air-filled chamber. Tremolo harmonicas in fact function with
much smaller chanbers than in the Discrete Comb, but the same sort of
response is not expected from them, and the player typically has four
such chambers in his/her mouth at any given point, allowing for greater
absorption of excess breath force. Also, the Knittler-constructions
AutoValve harp has dual-reed chambers of a very low height but greater
width as the blow and draw reeds are side by side.

For a dual-reed chamber such as found in the standard diatonic, larger
mouth holes may actually  help in overall response - the bigger the air
passage at the interface between the instrument and the player's body,
the better. But the question of reed chamber height and the related
question of overall chamber volume are ones that have not, to my
knowledge, been systematically addressed. Anecdotally, chambers that
are too large are known to cause problems, as in the reed chambers in
Holes 9 and 10 of the XB-40 in higher keys. In most keys this does not
cause a problem, but in the keys of C and above, the chambers have a
resonant frequency that is lower than the pitch of the reeds and pulls
their pitch down.

Winslow

--- J Compton <jofjltn4@xxxxxxxxxxx> wrote:
<snip>
>  
> As for what does (or might), how much work has been done
> experimenting with changing the comb thickness?  Most production
> harps seem to have about the same comb thickness (opening the door
> here for someone who has measured dozens of them to correct me and
> ridicule me for speculating where real data exists).  Is this an
> optimal thickness or just a traditional thickness?  I'd search the
> archives, but can't get there from work at the moment.  Please
> forgive me if a search would have yielded this info.
>  
> Also, what might be the next big development?  The recent Seydel with
> the stainless steel reeds is an example...maybe.  Any prediction on
> what might be next?
>  
> Jonathan "the future is hazy" Compton
> 
> 
> 
> > Date: Fri, 20 Apr 2007 08:28:46 -0700> From: zrkovacs@xxxxxxxxx>
> Subject: Re: Subject: Re: [Harp-L] comb material> To:
> harp-l@xxxxxxxxxx> > WHen? Im not gonna check back. If it is so, I
> am> sorry. I thought it was me. But to me it doesn't> matter who it
> was. If it was you, its probably all the> same. > > Zombor> > > ---
> Jeff roulier <jroulier@xxxxxxxxxxxx> wrote:> > > At 12:36 PM
> 4/19/2007, you wrote:> > > > >It seems I have stirred up still water
> (if there is> > >any saying similar to this in english) with the> >
> comb> > >material topic :-)> > > > > > Check the archives... I was
> the one who started this> > debate. > > > > > > >
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