I've seen the 'tear-drop' description used several times in this discussion. I think I know what it means but that remains my guess only.. For many others reading this discussion (if they are) it must be a fairly puzzling and unsatisfactory description.
What exactly are we talking about here? Francis On 28 Jan 2010, at 10:57, Philip Gruar wrote: > 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 > >
