The above is a frequency response plot of one of my T48’s. The cabinet is 25.5 inches internal width, loaded with 2 Delta 12LF’s. Pink noise from an O1V was sent through a dbx dr260, setup to function as a crossover only, no other processing was used. The crossover filters were set to about 26Hz and 2.5kHz. The signal sent to the cabinet was about 2V as measured with a voltmeter across the output terminals of the amp. The mic was a dbx RTA placed about three ft in front of the cab and about 2 ft above the ground. The mic fed into an old Behringer 8000 DSP to display the response. This was done indoors, so room size and placement probably had an influence. Two things caught my eye, though. The first was how closely the response matches what's advertised in the plans, especially from 60 to about 100hz, and the second was the upper range output. In practice, cut a few db around 125hz, and boost a bit between 40 and 50hz. They are used with either DR280’s or a pair of recently built OT12x2’s. If ever needed, I think the crossover could run up to 250Hz, but usually it's set to about 110-120Hz with the OT12's or to about 95 Hz if using the DR280's.
