Wayne--In my room, along the wall (2 boundary enviornment) and with the 6db at 30hz EQ of the Parts Express plate-amp used, I'm getting 25hz flat from a pair of 4648s, this according to my RTA with the mic placed where my head is when listening. I expected some gain in extension because the 4648 is rated 45hz F3 into a hemisphere but I didn't expect 25hz. I know that EQ below F3 with a vented box is generally a no-no but the 4-15s are so lightly stressed it doesn't hurt. Sound is deep and VERY dynamic, I'm very pleased.