The speaker also had a styrofoam(sp) cone. In the EV30W plans the full size speaker enclosure was 72cu.ft. but you could build a smaller version of it at 54cu.ft. I forget what the tuning frequency was for each enclosure. I had a chance to buy a set of these back in the mid 80's in the smaller enclosures, but it was kind of hard to justify 108cu.ft. of subwoofers in my living room at the time. Besides the cones were rare so if anything ever happened to them, or if I needed to get them re-coned I was SOL.