All H frames I have reviewed have been square profiles. Thinking aloud, but is there any value in a circular (cylindrical) 'H' frame. It will obviously be a larger diameter than the bass driver and generally about 7 inches to front and rear of the driver.
All comments appreciated.
FWIW, I experimented with putting 45 degree inserts into standard H-Frame corners to make an octagon port, took measurements and then cove cut concave corner inserts to turn the octagon port into cylindrical ports and took more measurements. I named the cylindrical version 8-Frames.
Ports were 13"x13" square versus 13" diameter round. Drivers were 12". Frames were 1.5" MDF.
There is something inherently disconcerting about pushing stock diagonally over the top of a spinning table saw blade to make the cove cuts.
Measuring at the mouth of the speakers, I got slightly higher SPL and slightly less distortion at higher frequencies. I presumed this is due to less port turbulence in the transitioning from the narrowest/horizontal/vertical width(13") to the widest/diagonal width(18.4") of a square port versus a constant (13") diameter cylindrical port.
13" is the quarter wavelength of @ 262Hz and 18" is the quarter wavelength of @ 180Hz.
The distortion started @ 250Hz and increased as the frequency increased. Using the H-Frame at lower frequencies did not exhibit the distortion leaving only the slight SPL delta.
Going from square to octagon made the biggest delta. Going from octagon to cylinder made a smaller incremental delta.
HTH
