That explains the differences in sensitivity. It's the faceplate. I have a pair of the larger Hi-Vi tweet on my "speaker junk" shelf. I wasn't all that impressed. With an advertised efficiency of 93 DB, I can't see using them with Eminence Alpha 10. The little Hi-Vi sounds better than the big one too. I don't know why, but it does. Bill probably has something with SB tweeter. I hope somebody tries the B-G planar. After I built the older one Pi speakers, and my son and his wife appropriated them, I've been contemplating a slightly larger floor standing version for myself. I really like Wayne's use of the Alpha 8. Maybe the B-G or SB tweeters would be a really nice upgrade for the one & two Pi models. The cost factor is reasonable.