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

   --


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