I would imagine they would act like Helmholtz resonators. I have heard and believe a story of Klipschorn cabinets being used as effective bass traps.
Possible effect I believe would be to pull out those frequencies, but generally, I believe and stand to be corrected, the small mouth openings would minimize this effect.
Possible effect I believe would be to pull out those frequencies, but generally, I believe and stand to be corrected, the small mouth openings would minimize this effect.