I've found this thread fascinating, as I have also experienced strain on the
wrists - strain generally in fact - when playing a set where the bag neck is
too short, and consequently have started to use bags (from Jackie Boyce)
with long necks when making my pipes. This keeps the chanter well forward,
and leads to a much more relaxed playing position. However, I'm aware that
there can be problems with the neck kinking and restricting the airflow if
it is too long and narrow. John's post about Helmholtz resonators seems to
suggest that a long narrow neck would cause more (or at least different)
resonance problems than a bag where the neck opens out broadly from the
narrowest point at the stock, "broadening smoothly into the main cavity" as
he says. If a narrow long neck makes MORE problems, then obviously we makers
should avoid that shape - if the gradually broadening shape makes DIFFERENT
resonance, then how different? Are the resonating frequencies going to be
higher or lower; more or less likely to coincide with chanter notes? I'm
afraid my maths isn't up to the calculation, and anyway - on looking at the
Wikipaedia article, I don't see anything about a cavity with pressurised air
inside, where there is a constant flow (i.e. from bellows inlet through to
chanter), let alone flexible resonators like pipe bags. No doubt the science
has been done, and it would be interesting to have some ideas, even though
there must be so many variables that it will be extremely difficult to come
up anything better than vague generalistions.
On the historical bag-shape question, the tear-drop shape of early bagpipes
certainly seems more suited to mouth-blown pipes, with the bag held well up
and in front of the body. Incidentally, I wonder if this shape is a natural
development from using an animal's bladder, stomach, or whatever rather than
making the bag from sewn leather? The swan-neck shape going into the chanter
would also make for ease of playing and no kinking of the neck (see
resonance discussion!). Adapted to the musette, and other early bellows
blown pipes e.g. illustrated by Praetorius there was the need for a long
flexible tube from the bellows. However, I would guess that both bag and
bag-cover are much more difficult and time-consuming to make than the simple
folded-over shape. Turning bags inside-out is surely only possible if the
leather is soft, and the early bags seem to be mostly made from quite thin
sheep or goat-skin. I wonder if the modern style of NSP bag - including the
excessively stiff leather sometimes used - is an influence from the Highland
pipe makers? What are the bags of the early sets in the Morpeth museum like?
I examined them all myself years ago and recall a variety of small, dried-up
bags and possibly early 20th-century replacements, but can't remember
details just now. Generally speaking though, I think most early small-pipes,
and also Irish pipes and Scottish lowland/border pipes which I have examined
tend to have small, squarish bags, shorter front-to-back and slightly deeper
top to bottom than what we use now. I don't recall the tear-drop shape used
in any late 18th/19th century British pipes.
However, several Reid sets I have seen had the most beautifully sewn and
turned (inside-out) bellows outlet tube. Now that's another whole thread to
become obsessed with!
Philip
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 27, 2010 11:44 PM
Subject: [NSP] Re: bag shape
I always understood the point of the open-cell foam in the neck is to
remove the neck resonance problem referred to earlier. The frequency of
this resonance depends critically on the shape - if you model the bag
as a big cavity with a narrow tubular neck,like a bottle, the formula
for a Helmholtz resonator applies - see wikipedia for this.
The formula will be quantitatively off as the shape doesn't really fit
the 'bottle' model well, the neck broadening smoothly into the main
cavity. But the order of magnitude should be fairly good.
If this frequency falls in the range of the chanter, the chanter notes
near this pitch will couple strongly to it and the pitch will be well
away from what you would get with the same chanter in a different bag.
Killing the bag/neck resonance means the chanter pitches will be truer.
As air can flow easily through the foam at low frequencies but not at
higher, the rapid oscillation of the bag/neck resonance is damped out,
without badly affecting the supply of air to the chanter.
I dread to think what clagging the open-cell foam with seasoning would
do to the airflow, though...
John
--
To get on or off this list see list information at
http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
--------------------------------------------------------------------------------
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.733 / Virus Database: 271.1.1/2650 - Release Date: 01/27/10
19:36:00
