For example,
Gypframe RB1 Resilient Bar
This product from British-Gypsum.com is used to “decouple” plaster board from ceiling joists or walls.
Decoupling, whether via aluminium diffusion bars or very expensive laminated dense-foam/rubber mats (used as an interface layer between a solid block wall and extra dense plasterboard, for example), is one approach to sound/audio/wave/noise attenuation design when “soundproofing”.
Draft proofing (or air-tightness) should not be underestimated! Apparently, even a key hole can leak an enormous amount of sound. Finish detailing on building fabric is critical to success = watch your builders like a hawk!
Ducted Mechanical Ventilation
If you’ve gone to the enormous effort of soundproofing you don’t want to bypass all that good work with open windows for ventilation, or taking the standard approach of drilling a 100mm+ hole in the wall and installing a basic extractor fan (without attenuation). There are all kinds of baffles that can be incorporated into air intake ducting to muffle sounds etc. You could even use a single room mechanical ventilation heat recovery (mvhr) unit, which could help with keeping heating bills down!?
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Incidentally, as a cheaper alternative to specialist sound rated bats, I opted for non-blown cellulose insulation (popular in the States and Europe), when building a load of internal partition walls, as they have a better sound rating compared to standard roll insulation. Although it is a loose-fill product.