i wonder what happens if fasih sees enerlevels systems 
anyway,
i have to agree with enerlevel about the manufacturer recommendations for a box. my 15" type R is supposed to be played in a 2.9cuft ported box. i made the perfect box according to the company specs and fed 900rms to a 750rms sub from a kenwood mono amp....and let me tell you - it sounded crap!!
than somebody told me that box sizes in company recommendations are a marketing gimmick - i have studied marketing and i know when a company is lying and when it is not
so some experts told me (from their EXPERIENCE) that type Rs prefer larger boxes and more port areas to reduce port noise....so thats what i did. made a 4.5cuft box for the sub and fed the same 900rms from the same amp...and man it roars now! it has come alive and have never heard a single sub perform that well. and its been 2 months in this BIG box and nothing has happened to the sub...this clearly shows that a 15" type R can easily and safely be used in a 4.5cuft box. 2.9cuft box is doing injustice to the sub.
so stop relying on books and theories alone...use them as well as practical experience.
moreover...polyfill can only VIRTUALLY increase size of box by not more than 20-40% and not to mention the other things that it will affect in the process of getting big.
the bigger ur boxes get (as in the case of vented boxes) the lesser the effect of polyfill and the lesser the chance of your fooling a sub to think its in a bigger box.
@faisi001: please dont try to make this into a competition. no one is better than the other...we are all learning here...teeli laganae kee adaat choor tou - ur very diplomatic ...we shud meet and have a cup of tea sometime
