My calculations show that a 4.1 cf enclosure tunes to 28 Hz with a 4 D x 7-1/2 L port, and a 2.8 cf enclosure tunes to 35 Hz with a 4 D x 7 L port.The M9500 uses 1400ND in a "Staggered Tuned" alignment. Enclosure Volumes:
78 liters (2.8 cu ft) 35 Hz tuning (upper LF)
115 liters (4.1 cu ft) 28 Hz tuning (lower LF)
Looking at the M9500 cutaway, the (folded) ports look quite long. Are the ports not 4 in diameter? Are my calculations wrong? Maybe I have the wrong T/S parameters.