Urgent advice needed about cavity wall insulation treatments

Hi guys, Havent been in the forum for ages, but i am in a panic here and need some urgent advice, My studio which i built last year (thread here viewtopic.php?f=2&t=13207 has cavity built walls, Mass, Cavity or air and then mass. So there is a guy coming today to reveiw the building for insulation purposes ( climate change making winters very very bad here ) and they want to fill the cavities in the walls with " insulation beads" I was not aware of this happening as my girlfriend planned and organised the whole thing ( lethally effecient woman!!! ) without discussing it with me, She had no idea this could affect my isolation soundwise and didnt imagine it would be an issuer at all, how ever i now dont have time now to study and read up to fill myself in ... To the best of my knowledge beads in the wall loose are ok and will still operate as air in a "mass air mass" wall setup. I assume if they use an expanding then becoming rigid foam type one its bad news regarding sound isolation but a bead type fill is loose so its ok right?? Its seems also they are going to fill our attic with rigid rock wool also ( Not to worried bout that one !!!) sweet ! I am going to get exact specs for the fill stuff when the guy comes, but this being ireland i wont expect to much knowledge from a contractor, Really I do need an educated opinion on this as fast as possible here, would be very gratefull if people could weigh in !! One Love DF

What type of "Beads"???? Most likely probably polystyrene: That is closed cell. No use, acoustically, sad to say! It will not help you at all, and will make matters worse, as compared to mineral wool. Doing it properly with mineral wool or fiberglass will gain you around 10 dB of isolation, and perhaps as much as 16 db. Those are big, worthwhile numbers. The idea of MSM isolation is that the "spring" (air) should be damped with the insulation. That's what removes acoustic energy from the system and turns it into heat. It does so by the vibration of the sound waves as they pass through the millions of tiny open air spaces in between the minute fibers, causing the fibers to vibrate in sympathy, thus converting sound into heat and removing it. Polystyrene is closed cell; it has no fibers, and therefore has nothing to vibrate, nothing to remove energy. That's why the typical polyurethane "foam in a can" is also useless for isolation: normally it is closed cell. But even if these "beads" are miraculous open-cell beads, that still doesn't mean they will work. In order to damp the spring correctly, the insulation must have the correct gas flow resistivity, measured in rayls. If that is too high or too low, it wont work. That's why you see recommendations here on using certain densities of rockwool and fiberglass: not because the density is a factor, but because products with those densities are known to have the correct gas flow resistivity. Unless there is published acoustic data for your "beads", showing their density and gas flow resistivity, and how they work as the damper on the spring in an MSM system, I would not do that. Do you want to be an "acoustic guinea pig"? :) I'd tell the insulation folks that what you want in your walls is either mineral wool at around 48 kg/m3 density, or fiberglass at around 32 kg/m3, that it must fill the entire cavity but without being forced into position: no squashing it to make it fit. Just lay it in place. Hope that helps. - Stuart -