Sound proofing a room has to do with two types of energy and the direction that energy is headed. The first is the energy generated from within the room to other adjacent rooms. The second is the energy generated from outside of the room. We do not want all of that outside energy to come in our room. It should stay outside where it belongs. We also want the energy generated inside the room to stay in the room.
Noise Stay Outside
To keep the energy that is generated outside the room such as car and truck noise, one uses a certain material type and a certain construction methodology to reduce the energy entering the room and energy reduction is our goal. We will never eliminate all noise issues. We must reduce noise levels below certain audible ranges depending on the room’s use. If it is a control room where recording and playback monitoring is critical to the product they are creating then there is a “quiet” number we can use for determining how much material we will need to accomplish our acoustic isolation goals. If it an office or conference room, there is another”quiet number” we can use that is a ratio of outside produced noise levels to inside produced noise levels.
Inside Our Rooms
Inside our rooms, we must use the same techniques we would use to keep noise from outside sources outside where it belongs. We would apply sound barrier technology and we would also employ another technique that of damping or absorption. Absorbing the energy inside of a room with sound absorption products contributes to room sound quality improvements for both vocals and instruments. Using barrier or sound isolation technology in the walls or inside the room would reduce the amount of energy from entering adjacent rooms and keep other external noises out.
Build The Wall
To keep outside noise energy from coming in to our rooms, we will have to use barrier technology. We must construct a barrier between our room and the source of the noise. If the noise is street noise, we must construct a barrier between our room and the street noise. We do this with mass. We use high density materials arranged and assembled in a manner that reduces structural vibrations from sound energy. Wall thickness and density depends on noise levels desired at what times within the room. Materials for barrier technology include poured concrete, lead sheeting, and even plywood. Remember mass is our friend and also layering of materials. Plywood has multiple layers of materials “sandwiched together”. Multiple layers of materials with different densities helps reduce vibrations which can translate into sound later.
Room Within A Room
One well used barrier technology method is to build a room within a room. One builds a new room inside the existing room that will be constructed of multiple density, materials arranged together to form a sound barrier to outside noise coming in. The existing room structure will also help us with keeping noise from the outside from coming in. In essence, we will have two walls of isolation. Just make sure both of those walls are mechanically and physically isolated from each other.
Damping or sound absorption technologies are used inside our rooms along with the barrier technology described above to keep the sound created in our room from “bleeding” into adjacent rooms. Our first focus inside the room is on low frequency or bass energy. We will want to use bass absorbers inside the room at specific locations to minimize the low frequency sound pressure levels due to the physical size of the room. Remember from past discussions, that room length, width, and height ratios produce low frequency and other frequency range resonances that are definitely unwanted. Foams or mineral wool type filled sound absorption technologies can be used to absorb unwanted reflections from our room boundary surfaces such as our walls and ceilings. Draperies can be installed with thicker carpeting. Pillows on couches and even thicker chairs will assist us. One company even uses activated carbon or charcoal inside its low frequency absorbers to generate large amounts of absorption in a small amount of real estate.
Soundproofing materials are selected based on their mass and density when it comes to sound isolation or barrier technologies. We need mass arranged in certain vibrationally reducing ways to contribute to high sound isolation numbers. Concrete, lead, and even plywood can be used in barrier technology. Sound absorption materials are designed to absorb energy and not reflect it as in barrier technologies. Bass traps and acoustical foams are examples of sound absorption technologies.