Resilient mounts with standard 13mm plasterboard

Hi, I would like to improve the soundproofing of the external wall of our build. It is a 90mm timber frame with external cladding. The wall has already been done, but not sheeted yet. I was thinking of adding furring channels on resilient mounts, will only add about 40mm to wall width and from datasheet seems like it will make a huge difference. To keep cost down, I was thinking of using standard 13mm plasterboard on the furring channels. But in the Gyprock installation guide it mentions only plasterboard with minimum mass of 12.5kg/m2 can be used? Like 13mm Soundchek, which is 3 times the price. Standard 13mm plasterboard has 8.5kg/m2. I know the performance will be a bit worse with standard plasterboard, but should it still be OK? Any idea why Gyprock mentions the minimum mass?

This is from the Gyprock installation guide: "The resilient mount has been design for use on ceilings and can be used on walls provided plasterboard with minimum mass of 12.5kg/m2 is fixed on the resilient mount side of the wall. "

Answer to first question: No it won't be okay.
Answer to second question: because mass is critical to suppress sound.

Sound suppression is very tricky so you need to do lots of research. Apart from mass the next critical issue is sealing any air gaps around the room you are trying to quieten. You can have a 1m thick dense wall (and ceiling) but if you have thin windows and air gaps around any window, door, ceiling cornice and any other opening you will improve things in only a minor way.
Lots of so called "experts" including window manufacturers, salespeople and builders have no idea about reducing unwanted noise so do plenty of your own research. Be prepared to pay for some time with a real expert - someone like an acoustic engineer who has had previous experience with home builds.

Hi, thanks for the info. We got good uPVC windows, but the walls are only 90mm timber with 14mm exterior cladding. I will follow your advice and pay a bit more for the heavy soundchek lining.

Will take care to fill all gaps. For a previous extension I used Sika expanding foam to fill all gaps. Seems to work really well to stop sound, or is there a better way to do it?

Yes there is a better way to seal air gaps. There is an acoustic sealant made specifically for that purpose - can't remember the name. Also look into better options for filling the gap between your 90mm timber studs. Like I said - it's a complicated issue to get right.

What we have done in a few theatres ( including my own) is run 2 layers of 13mm gyprock, but sounds insulation especially for the bass is really tricky as a lot of that noise can travel up the wall through the studs as vibrations. Aircon vents are also an issue so you need to have a think about that as well.

cheers
Simeon