Soundproofing - alternative methods?

I have bloody noisy neighbours, and am not fussed on hearing every word of their conversations. House is a early 1900's terrace with 9" brick party wall.

I want to sound proof two rooms in the house, one is simple enough - i will build a stud wall 1" off the existing, fill with rockwool and 2 layers of soundbloc board as space isnt really an issue.

However, the one bedroom upstairs is a problem. I cannot build a stud wall as i only have around 50mm to play with, as there is a window at a right angle to the wall that needs doing - if i come out any further than 50mm ill be past the glass.

Ive had a browse and the only thing ive come up with is what appears to be a 10mm rubber matting type material which is glued to the existing wall, then two layers of soundbloc glued over that (i believe its popular with the home cinema types). Has anyone used this to good effect? Or used an alternative that takes up little space?

I know its not going to be as ideal as a separate stud wall, just enough to stop us having to listen to them talking ***** would be nice!

Cheers

 

sorry, should have been more clear - the 50mm has to include the two layers of plasterboard. plus i beleive the stud wall should be spaced off the existing wall for better sound proofing.