Hey everyone, this thread is me clearing up a few questions I have about HDC3's and HDC4's. These are the two subs in question. (so it's easy to reference ) HDC3: http://www.soundqubed.com/HDC3118-Copper-Coil-Subwoofer_p_25.html HDC4: http://www.soundqubed.com/HDC418-D1-A-_p_137.html We are talking about 18" only Whats the story behind the high Fs of the HDC'4? Was this a non broken in woofer or something? The suspension is that stiff? (equivalent HDC3 is 9hrz lower IIRC) Between the HDC3's copper coil & the HDC4's aluminum coil 1. Can I daily an HDC4 on music? 2. Is there a large efficiency difference? 3.Why is the 4's coil an aluminum winding? Just weight savings and thermal dissipation? is it worth worrying over? Required cubic feet and port area? Do they want the same? & What do they want? Everyone loves pics.. First the HDC3: Then, the HDC4 Lets see what everyone thinks. p.s. Happy birthday M5