My bad i saw it on diy subwoofers http://www.diysubwoofers.org/faq.htm

Quoted:
1.06 - Can I use two short ports to replace one long port of the same diameter?
No! The resonance frequency (Fb) is proportional to the cross-sectional area of the port, and inversely proportional to the length. If you increase the effective cross-sectional area by adding another port, the length will have to INCREASE as well, otherwise Fb will go up!