Sennheiser takes advantage of this by using the same drivers in their whole HD5x5, HD5x8, and HD5x9 lines. Each line uses the same deiver elements, the differences in sound boil down entirely to the housing. HD595, 598, and 599 get the best housings and achieve the best sound. Many would mod the next model below to get the 595/598/599 sound for less money. I've gotten my HD558 sounding better than the three top models.