I'm having my walls soundproofed by building stud wall insulating and re plastering etc. I live in a semi detached house and hear my neighbours constantly...every noise ! Its been mentioned to me that the sound will also travel thrive the joists possibly and ideally need to be insulated . The issue I have it that I have wooden floors and I'm reluctant to take them up. I didn't know if a few small holes could be drilled in the 2 inch space where the stud will be built and expandable foam sprayed into them. I know it won't fill the whole of the cavity but I thought I may act as a void around the joists closest to the adjoining wall ?