Shallow pitched roof 4m square. 50x75 rafters topped with breathable membrane. Need is for some form of between-rafter insulation against heat loss BUT ALSO against noise from my Hi Fi. Whatever is used will be covered with 12.5mm plasterboards and artex skim. Presumably light rafters will impose a weight consideration and I would prefer to avoid Soundbloc plasterboard. Roof slopes from 2 up to 3.2 metres and a suspended ceiling is not an option. Ideas please.