Soundproofing A Finished Wall
The soundproofing treatment described here targets the reduction of noise bleeding through an existing finished wall. As we describe in our course on Transmission Loss here at the Academy, our goal with this sound control project is to isolate one room's noise from the next by impairing the common wall's ability to conduct vibration. The treatment outlined below follows the basic principles of sound deadening a wall: increasing the density of the surface and creating a disconnected structure.
Our first illustration represents a standard wall configuration. The single set of 2x4 studs support a layer of drywall for two adjoining rooms. As we illustrate in our course on Sound Transmission, sound energy flows freely back and forth structurally through these common studs. Regardless of what is stuffed between the studs, including fiberglass insulation, the studs themselves are the true culprit for sound bleed and the primary target for our soundproofing treatment.
Old school contractors will instruct clients incorrectly that a properly sound insulated wall should have batting insulation stuffed between the joists. We get calls every day from clients who have followed that advice and then call NetWell seeking help. The misinformation on wall soundproofing is out there, we advise clients to be wary. Follow the formula "density + disconnection" and you wlil succeed in soundproofing your wall.
STEP 1: DENSITY
Treating your existing wall does not mean that you have to tear out what is already there. We will just be adding sound control layers to your existing surface. These layers will serve to deaden your wall's ability to vibrate, disconnect your common structure, and destroy the transmitting energy by forcing the collapse of the sound wave inside your wall assembly.
Your first step is to line your existing wall with the weight of dB-Bloc. By adding density to your surface, you control your wall's ability to vibrate, and reduce its ability to transmit sound. The heavier your wall, the more difficult it is for noise to bleed through. dB-Bloc is a thin rubber membrane which staples direct to your existing drywall. The material is made of mass loaded vinyl that measures just 1/8" thick but weighs more than 150 pounds per 54" x 30' roll.
Our lab test results for dB-Bloc scored an STC rating of 26. When used in conjunction with a disconnected framing technique, the STC value of your finished wall assembly can jump from a standard wall rating of 38 to a luxury wall rating of 55-60. Results will vary depending on leakage, quality of construction, floor vibrations, ceiling plenum's, flanking paths, and a host of other factors that extend beyond the controls we are able to produce in a laboratory setting. Simply staple dB-Bloc to your finished wall as we show here:
You can overlap or butt seam dB-Bloc to the face of the studs with a staple gun. You can hang the material horizontal or vertical. Our test results are triggered with a single layer of the material on just one side of the wall, ideally the source side where the original sound is coming from. If you have a stronger budget you can apply a layer of the material to both sides of your framed wall. This won't double your results, but can trigger an additional 3-5 dB drop.
STEP 2: DISCONNECTION
Your second step in this treatment is to disconnect your structure by anchoring a set of horizontal firring strips to your wall. These strips can be made of simple slats of wood made available at your local building supply store. Simply screw one strip to the base of your wall, another to the top of your wall, and then every 16" on center up the wall. On the face of these new firring strips, you will then apply a new finished layer of drywall. This entire treatment will add just 1.5" of depth to your wall as we illustrated here:
RESULTS: YOUR STC RATING
As we teach in our course on the STC, a standard wall configuration will carry an average STC rating of 38. A luxury grade wall assembly will carry an STC value of 55-60. The target goal with this soundproofing treatment is to deliver a luxury grade rating to your existing wall. Please note that regardless of the treatment, results will vary for each application. The quality of the installation, the "flanking" paths that noise will travel through, vibrations through floors and ceilings, and a host of other issues will combine to decay your results. Rest assured that while no treatment can deliver a 100% drop in sound bleed, the layering treatment illustrated here can deliver a significant reduction, with as much as 90% of your unwanted sound eliminated.
Your treatment sequence: dB-Bloc + firring strips + drywall