Here is a useful page showing the various sound tests on interior walls. The whole web site actually has a lot of great info. It is by the Green Glue Company, supplier of the best soundproofing materials IMO.
Conclusion: Doubling up drywall doesn’t do much for stopping sound.
Resilient channels are pretty cheap but it is really hard to get them to work well.
Sound clips that fit into a hat channel work well with equal results to green glue but are slightly more expensive.
Green glue offers good sound proofing.
Steel studs are better than wood studs.
Bottom line: If you want to stop sound then stagger steel studs and use double sheet rock/green glue on at least one side. If you are totally nuts use sheet rock, green glue AND sound clips with hat channels.
As a green contractor in Brooklyn where houses are small and you have neighbors all around you, it is important to incorporate advanced soundproofing techniques as a matter of course.
And if you are going to do that for all green Brooklyn brownstone renovations, not just the high end ones, then you need to find affordable soundproofing options.
I find that staggered studs, good insulation, and sheet rock doubled up with green glue has great results. This also means you can reuse all the salvaged sheet rock that looks nasty but who cares since it is hidden.
This kind of thinking is really part of Building It Forward. Your normal client isn’t going to ask for this and won’t miss it if you don’t do it. Just throw in some sound board and tell them it is sound proofed and they will be happy.
But as a green builder you have to be thinking for them with these kinds of things and sound board isn’t worth a damn for sound proofing. The tests show this. To really Build It Forward and give a gift to future inhabitants of the house who will never know what you did behind the walls you need to build in good and affordable sound proofing techniques.
Nobody will notice if you do this, and that is sort of the point. They won’t hear their neighbors and won’t think why. They will just take it for granted. But you will know the gift you have given.
Even if you built normal and they did hear the neighbors you could just shrug, say that’s life in the city and they probably would agree. They don’t know any better.
But a green builder knows better. A green builder build’s “high end”, not in price but in quality, integrity and knowledge. That is Building It Forward.