Well I guess not ultra low but lower than 15.8 Hz. I'm going to finalize my inlaws' DIY speaker set with an EBS Tempest. I'm using the Adire LspCAD software. I'm going to be using the 340L box size but I'm toying with the idea of a low tuning frequency of 13.1 Hz with a 30" long 6" PVC pipe. This alignment is over damped but yields a flatter in-room response as reported by LspCAD. Of course the group delay is reduced as well. Should I put any trust in the room response numbers in LspCAD? I also have the full version of LspCAD, would it be a better judge of room response? Thanks.