Sound Transmission Loss
The soundproofing treatments outlined here target the reduction of noise bleeding through a common surface. To understand this set of treatments, we recommend you first visit the courses here at the NetWell Academy on Sound Transmission and the STC. In both courses, we discuss in detail how noise bleeds through your surface and how it is measured.
The first ingredient in your sound control solution is to come to understand how noise actually transmits through your surface. The following illustration highlights the motion of sound energy transferring along from molecule to molecule through air or structure, much like doing the “wave” at a sporting event. The transfer of energy takes place through vibrations that pass the sound wave along through neighboring cells that comprise the air we breathe and the structure that defines your room.
Next, we note that this energy transfer can take place within any matter that comprises the world we live in. Metal, wood, steel, concrete, air, water and drywall are all made up of molecules. This helps us define the first of two ingredients we need to combat the transmission of noise: disconnection. Unless the walls, ceiling and floor of your room are properly disconnected from the structure of your building, noise will always have a direct path for leakage. To illustrate this point, we refer you back to your childhood. Recall when you were able to pull a string tight between two coffee cans and communicate back and forth with your friend. The molecules that comprise the string would accept the vibrations of your voice and transmit the sound back and forth through energy transfer. If a scissors were to cut the string, the structural contact points would disconnect and the sound transfer would collapse.
With any wall, ceiling or floor system, if there is no disconnection in the structure, the supporting studs, beams or concrete substrates will serve the same function as the string. Energy can transmit back and forth through these common contact points as easily as it can through air. Structure borne noise becomes as big an enemy as air borne noise. In the following illustration, we highlight the configuration of a standard studded wall that is used to build most of today’s homes and offices. A single set of studs that support drywall on both sides is the least costly way to construct a room. Unfortunately, the studs become the common contact point that will deliver sound energy back and forth, while stuffing the walls full of fiberglass batting will do little to combat the bleed of noise.
The second half of our equation in combating sound bleed is to add density to the common wall surface. When air borne sound waves reach a common wall, the wall will ebb and flow in tiny oscillations invisible to our eye. This is the surface accepting the resonance of the sound wave. The more the surface is allowed to vibrate, the more sound energy will transfer through the surface. By adding density to the surface, we slow its ability to vibrate which will decay the amount of noise able to transmit through. The density portion of your sound control solution is simple. Simply line the common wall, ceiling or floor with dB-Bloc:
dB-Bloc is a thin, weighted, mass loaded vinyl that measures less than 1/8″ thick but weighs more than 150 pounds per roll. This heavy, limp material is designed to layer behind a finished wall surface to help deaden sound transmission. When used in conjunction with a disconnected framing technique, the use of this material can trigger up to a 90% drop in noise bleeding through a common surface.
Creating a disconnection in your common surface can often be the more difficult and invasive procedure. The techniques used will depend in large part on whether your wall is existing or a new build. We outline both techniques below:
For New walls
Here you have the advantage of triggering your disconnection with either of the techniques listed below. A double wall or a staggered stud assembly system will give you the collapse in sound transfer you are seeking. Either technique will force a transmitting sound wave to collapse inside your surface. Most framing contractors know of these techniques, but most construction companies opt to not build them due to the added costs.
For Existing Walls
The majority of our clients call with an existing wall assembly already built. The ability to create a staggered-stud or double wall construction doesn’t apply. The next best alternative is to simply staple dB-Bloc to the wall as is, and secure a horizontal set of firring strips up the wall. Furring strips can be simple 1×4 slats of wood every 16″ on center, or you can opt for the ISO clips and resilient metal hat channels. Either technique will then provide a new surface to mount your new layer of drywall to, that will now “float” away from the structure of your building. This illustration is outlined here:
The floor/ceiling joists serve as the same culprit to noise transmission as the studs inside the wall. Your goal is to line the common surface with density, and create a disconnect by either “raising” the floor up above or “lowering” the ceiling down below. dB-Bloc and FloorFighter are your barrier components, while your disconnection techniques are outlined in the Floors or Ceilings section of our Application Guide.
Regardless of your best efforts to combat the sound transmission through common wall, ceiling or floor surfaces, your enemy will always be the “flanking paths” that noise can take. These are any and all openings in a common surface that will allow noise to bleed and deteriorate your results. They include vents, outlet plates, switch plates, light canisters, exhaust fans, pipes in the walls, doors, windows, and tiny air pockets behind door and window casings. To help ensure the success of your treatment, we recommend you apply acoustic caulk to all open seams, cracks and joints in your treatment to help minimize the effects of this unwanted bleeding.
To recap, the sound you hear is 100% air borne sound. But the path the sound wave has traveled to reach your ear drum has quite often traveled structurally first to gain entrance into your room. The surfaces will vibrate to the resonance of the sound wave, delivering noise back and forth through the common contact points. Your goal in a successful sound transmission treatment is to decay the vibration rate of the surface by lining it with density, and then severing the contact point as best you can to force a collapse of the wave inside your wall, ceiling or floor surface.
See Wall Treatment See Ceiling Treatment See dB-Bloc See FloorFighter Back to Sound 101