Sound Isolation

SOUND ISOLATION

Acoustic Education
 
Sound Isolation can be defined as the degree of acoustical separation between two locations, especially adjacent rooms. When dealing with sound isolation you must consider that only two things stop sound - mass and space. You need mass to contain the airborne sound, and you need space, (an air gap or similar unobstructed area), so that the structure borne sound cannot be transmitted.

Most vibration and sound transfer from a room to the outside occurs through mechanical means. The vibration passes directly through the drywall, brick, woodwork and other solid structural elements. When it meets with an element such as a wall, ceiling, floor or window, which acts as a sounding board, the vibration is amplified and heard in the second space. A mechanical transmission is much faster, more efficient and may be more readily amplified than an airborne transmission of the same initial strength.

To eliminate structural borne noise, you have to break the connection between the room that contains the noise source and the outside world. This is called acoustic de-coupling or sound isolation. De-coupling a wall used to be accomplished through the use of staggered stud construction, which is done by using a 2” x 6” top and bottom plate then staggering the studs, decoupling one side of the partition from the other. A more efficient and economical solution is to use resilient isolation clips and furring channel. Resilient isolation clips use a patented rubber isolator that isolates the gypsum board or plywood from the structure reducing noise transfer by 75 to 100%, adding 15 to 20 STC and IIC points to existing assemblies. The clips fasten directly to the framing creating a 1 5/8” cavity between the face of the framing and the back of the gypsum board. A mass loaded vinyl noise barrier can be used in conjunction with resilient isolation clips to reduce airborne noise and further increase the acoustic performance of the partition.

Sometimes it is necessary to isolate an entire room from the surrounding spaces such as in a music practice room. Resilient isolation clips can be used to essentially build a “room within a room” by decoupling the walls, floor, and ceiling. Ideal de-coupling also involves eliminating vibration transfer in both solid materials and in the air, so air-flow into the room is often controlled with HVAC silencers. The acoustic performance of a wall is only as good as its weakest link which are doors and windows, so those need to be acoustically rated as well.

Industrial noise isolation typically involves preventing equipment and machinery from transmitting vibration through the surrounding structures. Common examples are rooftop HVAC units and circulation pumps. The most common solution is through passive vibration isolation which utilizes products such as vibration pads and mounts, mechanical springs and dampers, and pneumatic air isolators. A passive isolation system in general contains mass, spring, and damping elements and moves as a harmonic oscillator. The mass and spring stiffness dictate a natural frequency of the system. Damping causes energy dissipation and has a secondary effect on natural frequency. The main factors that influence the selection of passive isolators are the size, weight, and movement of the equipment being isolated, as well as ambient temperatures and potential corrosive environments. Active vibration isolation systems contain, along with the spring, a feedback circuit which consists of a sensor a controller, and an actuator. The acceleration (vibration) signal is processed by a control circuit and amplifier. Then it feeds the electromagnetic actuator, which amplifies the signal. As a result of such a feedback system, a considerably stronger suppression of vibrations is achieved compared to ordinary damping.