I was all set to use Quiet Rock ES to keep noise from getting through an interior wall, but our supplier was out of stock and instead selling Cetainteed Silent FX. Anyone know which is better? The Slent FX is about $5 per sheet cheaper. Thanks.

depends on the noise you're wanting to block. there are acoustical consultants for these things.

for low frequencies, nothing beats mass. for mid to high ranges, insulation for the highs and either air-cell or metal center acoustic drywall, dependent on the frequencies most annoying.

if you're trying to quiet down a media room, mineral wool batts in existing walls with high density wallboard on both sides would be good. if you're remodelling, consider a wall with a 6-inch plate and 2x4s staggered to leave a non-continuous surface, and then fill all spaces with mineral wool batts.

if it's going to be studio-grade, you want a consultant for sure, but some things to consider right off the bat are no parallel walls/floor/ceilings, sand-filled block with isolated finish walls, absorbent panels or tuned-metal damping panels, etc.

Really helpful information, thanks a lot. Just wondering if cotton insulation ( like UltraTouch cotton batts ) might not be about as good as the mineral wool batts you mentioned. Seems like the cotton might have as much or more mass, but is there more to it than that? Thanks.

no clue. the absorbtive element of insulation is based on lots of little tiny air cells, all isolated. I have no data on the jeans insulation.

OK thanks. Another question, do you know how you are supposed to install batt insulation on a staggered stud wall to maximize sound reduction. I would think horizontally would make for less joints and a better seal, but it would also create more air cavities with no insulation. Any thoughts on this one. Thanks for the help.