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