OK the 3 cubes for a 15 is easy i do it an i have that same peaky response with my rd but its for spl so i like it like that. far as tuning down to 29hz lol with 3 cubes thats not much port area really. i mean 3 cubes thats about what 30sq of porti think. if not smaller. or one long *** port which will cut down on cubic feet which will raise tuning but i don't know i am just talking off the top of the dome.