I am helping my son renovate an old Victorian terrace house (on a tight budget). We have had to remove a bedroom ceiling due to nail rot on the laths. There is another floor so although it’s a bedroom there is another above it. The plasterboard costs are about £86 but rockwall sound insulation is £256. Question is is double boarding the plasterboard as good as 100mm rockwall sound batts?

Resilient bars seem to work fairly well and I think if you combine these with double boarding it will be better than rockwool. The British Gypsum White book has some details for floor / ceiling constructions and the sound attenuations.  Even a couple of decibels makes a lot of difference.

I use a lot of expensive acoustic insulation in my job But yet used 

Wickes loft roll in ours 

The Acoustic insulation is there to stop the sound bouncing around 

As pointed out Res bar and single 15 board will make a big difference 

also