For thickness, it really depends on the purpose. For example, if you are building a bass trap, you need, not should, you need 3-4″ thick to stop the wavelength of that deep bass below 125Hz. If you are creating panels to deal with high frequency reflections, then 1 or 2 will be perfectly fine.

For example, here is some data on the rockwool from acoustimac for the panels. What is funny is even when there isn’t data on the insulation for these factors, all insulation of similar type will be in the ballpark, so safe n sound will do the job.

What the coefficient means is the percentage as a whole number for stopping a sound at a given frequency, often tested up to 4,000Hz, with NRC being the average of all frequencies. The way measured, you can technically get 1.15, or 115%. So, when you see it around 0.9 or above, that is going to dampen 90% or higher in that frequency range.

But it is hard to go low. It is said around 15-20% isn’t doing much at all, so when you see 0.2 or less, the insulation for those frequencies will do nothing. So, that means you can use the thinner 1″ and 2″ for helping with mids and highs, really above 250Hz for 2″ Rockwool 60 (about 80%; at 500Hz, it should be over 100%), and 500Hz and above for the 1″ (about 80%, but that is stretching, above 1kHz is definitely fine). For 4″, that will take care of down to under 125Hz.


This is better than the Roxul (which is rockwool subsidiary) 40 in the chart on the page showing 1.03 at 125Hz, meaning 100% dealing with that deep bass and likely even efficient much lower than that frequency.

Also why the Safe n Sound you have will do great work in knocking down even low frequencies.

Now, are you insulating the walls and floor/ceiling of the room below, or are you building room treatments? If just insulating, then there are certain treatments that can be done to the walls, you could use polyurethane membrane between two layers of drywall, you could even put mass loaded vinyl in sheets in front of the insulation but behind the drywall. I doubt you care to go full out (because full out is intense) due to cost of doing a second set of studs, then you have insulation, a 2″ space, then insulation between studs again, then the MLV sheets, then dual layer drywall with polyurethane, then the poly sealant around the edges, etc. Overkill!

With speakers, unless you want to build a massive enclosure, trying to insulate a sub is futile. But, if you can track the reflections for the subs, you can build traps to deal with first, and possibly second, reflections that can help to control it. What people often do is build a wood frame to hold the insulation, then they get an acoustically transparent fabric and have something artistic printed on it, that way they only have to stretch that over the trap and they can hang it like a piece of art. That helps with the WAF and can really tie the room together.

So, what thickness to use really depends on how it is being used and for what frequencies it is meant to address.


Edit: did some calculations and if that is the 39lb package, and assuming the absorption coefficients on that website are correct, then that is about 53% effective at 125Hz and 96% at 250Hz for the 3″ safe and sound. So it can help trap some bass, but seems the 4″ I tagged will have a better effect if looking to make some bass traps.

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