I have been called “A Renaissance Man”, which is a bit embarrassing to me. However, 22 years ago for a period of 18 years, I had multiple careers, doing music at night (singing in a show or playing lead trombone in a big band) but I also had a “day gig”. I got licensed by the Board of Architecture and by the Contractors Board. Part of my tests included acoustics. It was a must to understand sound transmission control. It also was a must to understand acoustics because it was on the test.
I had the pleasure of drawing the plans for the mixing room which was built at NBC Burbank, CA, where the Tonight Show was filmed (back when Johnny Carson was on it). Sound behaves similarly to light with absorption, reflection, dispersion and in other ways. Sound is a vibration and a floor slab can be affected by ambient sound.
Some studios isolate the slab from adjoining areas by literally cutting it away (if remodeling for a studio) or by isolating it during the pouring of concrete if it is new construction. Many things can be done for sound transmission control. Sometimes there is a space between a double wall. Sometimes resilient channels are used to mostly isolate gypsum wallboard from studs or furring strips against a concrete or CMU wall. Sometimes insulation is used within the walls. There are several types of assemblies which have been tested and are designated by STC ratings.
At NBC, there were 2 layers of a foam-type material between the bottom plate of the wall and the floor slab. In this instance, there was concrete, a foam rubber material, and then the wood bottom plate. The wall was built with a space between it and the concrete wall that it paralleled. The side walls additionally were covered with Auralex. There site is here:
The front of the room was glass and a “normal wall” , creating an LEDE design (live end-dead end. The interior walls were set with a laser transit to tolerances in the thousandths of an inch and none were parallel, nor was the ceiling parallel to the floor.
There is a lot more to consider than materials, when controlling sound transmission. Some people say that lower frequencies, such as a bass will pass through concrete more easily than higher notes. Yet, as I sit and type this, in a concrete “flat plate designed” building, I can hear the lovely young Italian harpist playing over my head. Understand that there is a concrete floor between us, the underside is covered with gypsum material and her floor is covered with a carpet and padding. I can hear all frequencies of the notes she plays. They are not loud, but are audible.
I have designed condos, recording studios, churches, hospitals, stores, many houses (approx. 2,500), and radio stations. This also took place in West Virginia, Ohio, Kentucky, and Florida. Being a musician and a singer, I always thought about sound and was eager to learn more about it.
A good question might be which materials conduct, transmit, reflect, and/or absorb sound. Each has its own quality. It is possible to soundproof a room but it is also cost prohibitive. If you are building a studio or music production work space, you’ll have a budget to consider. Fiberglass insulation does not conduct sound well. Styrofoam insulation may conduct sound slightly more than fiberglass insulation.
Sound will travel through air and water, so molecular density is a factor and so is the frequency of the vibrations involved. There are people with much more theory behind this, acoustical engineers, and they can always be consulted for in depth ideas, too.