Q: "How much studio foam do I need to 'soundproof' my room?"

A: To answer this question, we're turning to our friends at Auralex who have the following to say on this topic:

This is probably the single most common question (or variations on the same theme) we encounter here at Auralex. Unfortunately for many folks seeking an inexpensive cure to their sound woes, acoustical foam is not it. Acoustical foam (and fiberglass and acoustical blankets and mattresses and curtains, and so on) is an acoustical absorber. Foam is ideal for improving the sound in the room, but does little to stop sound from leaking into or out of a room.

Absorption and isolation are two separate phenomena. Imagine firing a strong stream of water at a large sponge. The sponge itself would become saturated with water, but if you stand on the other side, you will notice the stream coming through the other side - an absorber at work. If on the other hand, you fire the same hose at a brick wall, most of the water will reflect off and very little, if any, will go through - an effective barrier.

Good sound isolation results from two main details: density and air gaps (or, more specifically, decoupling of structures). Density is in the form of materials such as drywall, chipboard, plywood, soundboard, vinyl barrier products (such as SheetBlok), lead, etc. Air gaps between existing and new walls should, if possible, be at least 2 inches wide. (But even air gaps as small as ½-inch will serve the purpose of decoupling the structures.) The combination of density and air gaps will provide varying amount of isolation depending mostly on quality of workmanship.