Note: If it is in fact peaking around port tuning frequency, which might be interpreted as 'boomy' if it's not room acoustics causing the 'boom', then you can add additional acoustic dampening/stuffing in the box and reduce this effect, if so desired. Also note that with this size enclosure, and 150 watt amplifier, you could later drop in a high quality driver like the Infinity Kappa Perfect VQ 12 w/midQ motor insert and plug up the port on that cabinet to make it sealed. The result would be a -3dB of around 34Hz, -6dB by 27Hz and -10dB by 21Hz. This woofer would provide extreme low distortion and reasonably high output levels with this amplifier.
-Chris