I am a little afraid to give you advice on this one...... because it is not for all. What I mean is YES, I love what it did to the tactile bass! It is just what I wanted and most make a comment at some point in a movie about it. But it might be too much shaking for some here.... I think it depends on the person. But to answer your questions if you do 2X4 flat make sure you have even more bracing points than normal. Yes, I used only one locking layer of the 3/4OSB same that is on my main floors in my house. No plywood, not for response reasons on that one but plywood can fall apart over time. I used to SkateBoard all my life and always had plywood issue with all the ramps I have made, man I just could not consider using it on my floors. Everyone here told me I should use two layers and maybe they were right. Because as well as I screwed the floor down and waited for it to settle down on warping before screwing in the last screws. I still have one spot that creeks in one corner. For me it was a small sacrifice for the extra tactile bass response. But I can not recommend this to others. I would feel really bad if later they came back and complain about it creaking and all I have a feeling the effect can be more safely done with close to same tactile bass response by just doing your whole floor with those floor panels.
Good info. I love the upstairs response with just 2 budget 15" subs on a wooden floor compared with 4 18's downstairs on the concrete. I've been reading that for best response you don't over-build the floor or riser so I was already planning on the one layer of 3/4".
Denon AVR-X4200W / Crown XLI 2500
7.4.4 Klipsch Ref. ii & In-Ceiling Atmos / Titan-615LX center
NU3000DSP - 2 SI HT18 D4's / NU6000DSP - 2 Ultimax 18"s
BenQ W1070 / 120" AT screen / Volt-10LX Atmos build