Recording musicians can face a variety of problems with unwanted noise. Sound from monitor speakers and instruments can leak into neighbours' properties and cause a nuisance, but equally, noise entering your studio from the outside world can make it impossible to record properly. In both cases, the best answer is to improve the sound isolation of your studio, because sound isolation treatment works the same both ways: what stops sound getting in to a room affects sound getting out to the same degree. However, there's no lightweight 'magic bullet' to solve the problem, and the foam materials you use to improve the acoustics of your room will have little benefit in terms of sound isolation. Likewise, despite long-standing urban myths to the contrary, egg boxes stuck to the walls have virtually no effect on sound leakage!

In the context of a small studio, the term 'soundproofing' is actually rather misleading, because the best you can really hope for is to improve the situation. Eliminating all sound leakage is virtually impossible in the types of buildings used for housing and typical domestic or project studios. So what you actually need to determine is whether the measures you're able to take (both practically and economically) can reduce sound leakage to a level that you find acceptable. I've tried to write this article with this in mind, and most of the steps described here should be within the scope of a DIY enthusiast. The necessary materials should be available from your local builders' merchant or by mail order from a studio materials supplier (such as, for example, in the UK).

If you were paying attention in your elementary physics lessons, you'll know that sound is acoustic energy and that, as with any other form of energy, it cannot be destroyed: it can only converted to another form of energy. Sounds die away naturally because their vibrational energy is converted to (a very small amount of) heat, either due to friction in the air itself or in moving (vibrating) the objects it encounters. Sound also reduces in level the further it travels from the source, as its energy becomes spread over a larger area — something that we know as the inverse square law, due to the fact that the sound intensity of an omnidirectional source reduces relative to the square of the distance from the source.

More precisely, sound is vibrational energy in the audio frequency range that passes through the air, and can also be conducted via solids or liquids. Though airborne sound can't escape directly from an airtight environment, its vibrational energy causes the walls of that environment to move and they in turn launch new soundwaves which can be heard outside. This gives us our first clue as to how to contain sound: we need to reduce the amount by which the walls can move.

Materials of infinite stiffness may be available in Star Trek, but in the real world they simply don't exist, so the simplest thing we can do is to add mass to the walls, because the heavier an object is, the less distance it will move for a given amount of applied energy. From this, it follows that if we double the mass of a wall (for instance, by doubling its thickness) then a given amount of sound energy will only be able to move it half as far, which in turn means that the amount of sound leakage will be halved (reduced by 6dB). We can also choose 'lossy' materials that aren't very efficient in transmitting vibrations. As an example, a given thickness of glass may...