The box measures 9"x20"x22" for 1.6 ft3 or 45.311l. It has a 2" port. I made the first port 3 3/8" long which according to this site(http://www.bcae1.com/spboxnew2.htm) tuned to 34 Htz.. In testing the port wistled badly below 40 Htz.

Speaker Specs:
I have made another port at 5 1/4" and I think it works better. It is tuned(by software) to 29.5 Htz. I does wistle but not till down at 28 Htz.

Any body know what the disadvantages of tuning lower are??

http://www.blaupunktusa.com/NR/rdonlyres/A836F9A4-C803-41C0-8957-0905208B025C/5710/ProComponentSubwooferSpecs.pdf