My DIY fully horn loaded speakers uses Bill Fitzmaurie designed HT Tuba folded corner horn subs, quarter wave horns turned to 25 Hz. Output measured at the listening position with my trusty Radio Shack SPL meter of the DSPed system (DEQX) shows the output at 25Hz to be identical to the output of the 1kHz reference tone. Roll off below 25Hz should theoretically be at 18dB/octave but is in fact a bit steeper than that.
The subs are 2ft.X3ft.X3ft. or 18 cubic feet.
The subs are 2ft.X3ft.X3ft. or 18 cubic feet.