I'm in the process of renovating the 2nd story of my New England 1.5 story cape-style home. New OSB subfloors are down with Liquid Nails and deck screws over 5 weeks ago. I'm on to flooring now. I don't have much experience with wood flooring, so I'm not sure what my best option is for reducing traffic noise from upstairs into the rooms below. I'm not too concerned about moisture, except moisture content of OSB. The house has forced hot air heating. Can I use a felt cushion underlayment designed for floating floors in a nail down application of solid hardwood? Does rosin paper act in any way as a noise barrier?
You probably missed "the best option for reducing noise to below" if you put down new subfloors and didn't put insulation under them (assuming you actually removed the old subfloor and had open joists.) Your next-best option would be to blow in insulation from below.
If you are already committed to nail-down flooring, I don't think the underlayment will make much difference, as the nails will transmit sound into the structure. An actual floating floor on the thin, dense foam underlayment sold for that purpose would be the best option on top of the subfloor for traffic sound reduction - or a "no shoes on the second floor" house rule.
Disclosure: I'm a DIYer, not a pro. A lot of the noise you get will be "impact noise". Insulation reduces acoustic noise, not impact noise. Also, I believe that a lot of the impact noise hits the joists, runs along the joists, and goes down the studs. Especially if your house is balloon construction (which it probably is). Balloon means that the 1st and 2nd floors are one unit, and the floor is nailed in halfway up the wall. The other type of construction builds them more as two separate units plonked on top of each other. Sorry if you already know that (but perhaps the next person to read this won't know it).
I just noticed this question is 7 years old. sigh
All that being said, your best bet is an impact noise underlayment under the wood flooring.You want to check its IIC, which is the standard for measuring impact noise (there is another acronym for the standard for measuring acoustic noise). We are using Floor Muffler Plus, mostly because it's available at HD. It has an IIC of 72-ish, which is pretty much the highest right now. There are other comparable products.
If you look at MF's website, you see a product with plus and without plus. I think the plus means it has tape, to tape the strips together. Probably easier for DIYers. Also, on MF's website the product is green. On HD it's orange. O la la! There is no difference between the green and the orange.
Other products include QuietWalk (which also has a Plus version, of course). Google "impact noise abatement". Make sure the products you look at are for Nail Down.
Also, we actually did put a ton of fibreglass insulation in the downstairs ceiling and in my opinion it has done nothing, except to make wiring more of a pain.
BTW, in the old part of our house, we have zero impact noise, despite the balloon construction. The joists are hefty, plus they are spaced closer together than the current code requires. You might not get too much noise, given you're in an old house.