[Huskerbryce]

I have lots of room absorption and diffusion treatment on the ceilings, corners and walls.  In an effort to further help the sonic behavior of my room I have considered placing a 2lb/sq ft mlv layer between the rug and rug pad.   Danny uses the no rez with it attached. My thought is that the lower frequencies would be further dampened by the vinyl.  Would it be effective in the 150-400 hz range? Its about a $300 experiment.  Has anyone tried and measured the result before and after??  Am I totally off in my thought process and wasting my money and time?

[Solarflares]

Probably better to use 12” heavy-duty extra-springy foam-rubber.
At least that way, if it doesn’t work - you can recoup the cost by renting the room out to kid’s parties as a musical Bouncy Castle.
That’s assuming you can make Jelly of course.

[g3rain1]

What you are describing is a tuned damper, all be it not a very well constructed one. Typically they need a sealed air space behind to work properly. Also more air space than a rug pad can provide.   And you only ever want to use tuned dampers strategically, with a know issue at a specific frequency and a damper tuned at that frequency.  Just throwing one together haphazardly will more likely just create a new problem where there wasn't one before.

[Solarflares]

Typically they need a sealed air space behind to work properly.

Correct.

[Huskerbryce]

I guess I was thinking it would act more in the velocity based damping rather than pressure based. 

[g3rain1]

I guess I was thinking it would act more in the velocity based damping rather than pressure based.

Velocity traps need to be porous. Vinyl isn't.

[tomlinmgt]

You're going to have to use 4" or thicker absorption to have a velocity based device that will work in that range.