Hi GarMan, I have built both. I have 4's at my house and I built the 3's for my Brother. I visit him about every week and usually watch a movie or listen to a few cd's every time I go over, so I have lots of experience with both. We own nearly identical associated equipment as well. Theater 3's are incredible for the size. I guess it is the "LF" aspect of the driver that allows it to keep up with the 15. I often use a 40 watt/channel crown and for this I favor the 4, but at higher power(Adcom 5500 at Bro's) I actually prefer the 3. No reason i can pinpoint, just a subjective difference. In fact we were shocked at how little difference there is. I would be enormously impressed if anyone has designed a smaller speaker that has such terrific bass and power handling. The 4 comes off a touch fuller and warmer, but his room is bigger than mine and has a different sound. I bet differing room acoustics exceeds the degree to which they sound different from each other. In my opinion you have no need for want at anywhere near this size and price class. Thomas