apples and orages. the two subs use completely different motor designs, and are meant for totally different uses. the type R is an all around all purpose SQL sub and two type Rs will be a lot louder than one type X. the type R is suited best to a ported enclosure as well. the type X is a high excursion SQ driver best suited to a sealed box and made for rigid linearity applications.. just because it has a deep basket and a big magnet doesn't make it an SPL sub.