Calculating cabinet volume - am I doing something wrong?

I am building a cabinet for these but am a little surprised that the calculated volume I get after I have run the numbers through several different calculators is so low (11-12l). Some give me dimensions that won't even encompass the length of the port that it needs. Am I missing something?

IMG Stageline SP-10/150PA
Technical Specification

Impedance (Z) 8ohm
Resonant frequency (fs) 60Hz
Max. frequency range f3-5,000Hz
Music power 300WMAX
Power rating (P) 150WRMS
SPL (1W/1m) 98dB
Suspension compl. (Cms) 0.19mm/N
Moving mass (Mms) 38g
Mech. Q factor (Qms) 5.36
Electr. Q factor (Qes) 0.30
Total Q factor (Qts) 0.29
Equivalent volume (Vas) 34 l
DC resistance (Re) 6.9ohm
Force factor (BxL) 18.2Tm
Voice coil induct. (Le) 0.94mH
Voice coil diameter 65mm
Voice coil former Kapton
Linear excursion (XMAX) ±4mm
Eff. cone area (Sd) 350cm2
 
This is intended for midrange. Look at the xMax. Low Vas , Qt sacrifices bass extention for efficiency.

STageline-SP-10-150pa.png


I’d put it in sealed 6 litres (damped) and XO at or above 150 Hz. 300 Hz would be better.

dave