Every acoustician and designer has his or her elements that work for them, such as, double wall construction, double/triple drywall layers, vinyl sound barriers, puck mounted floated floors and so on. There are variations and substitutions to all of these (staggered studs, resilient channel, rubber pads, etc…) and these are the hidden elements, the ones that are taped, spackled, painted, fabric wrapped, carpeted and made to disappear for higher aesthetic.
The basis and core principles are standard practices of acoustical construction. Dot your I’s and cross your T’s and you will deliver a competent shell and palette for a more diverse philosophy of sound design. This is the voodoo of some of the great sounding spaces we’ve built. For example: THX licensing demands thorough construction methods with specific material, such as Quiet Rock, which is a multi-layered drywall material which includes a dampening compound between layers of ¼" drywall, metal, and a cementitious substrate. It is heavy, it is expensive, but when installed properly, it works very well and it is required to comply with THX licensing rules.
There is a magic to the material & labor intensity involved. Mass and density deadens the projected sound and the different and multiple layers of materials diffuse the energy and heat that the sound emanates. This is your base prior to the expansive THX sound design, physicist enabled theories that will ultimately ensue. On the other hand Dolby certification demands precise dimensional standards, while editing facilities need, minimally, to be isolated from one another. The underlying theory here is to look at any room that you want to acoustically construct as a room within a room that can have no rigid contact with any other surface but itself (and sometimes not even itself! But more on that later).
An example I use to describe this method to trades or crew that need an understanding of what sometimes seems like an over-built room or detailed busy work is this metaphor: This room needs to hold water. If it were to be filled with water, which area would it leak at? That is the area that needs attention. Build a tight ship, this is the foundation that everything else will rest upon.