Interesting. I always associated the term with the usually hidden bass tubes in a pipe-organ, built of wood in a square cross-section. The one in our Church as I recall is about 14" square, 8 ft. long, and puts out a tone that you feel more than hear. I used to love singing in the choir, the loft being right in front of the organ rack, and having that bass box just rattle our bones with a powerful harmonic frequency with what we were singing (I was in the Bass section). It made the little creepy-crawly titterjingles run all up and down my spine and my ears vibrate in harmonic resonance. It's about the next best thing to getting lit up with the Holy Spirit! Glory!