How Sound Insulation Works? Sound is transmitted when vibrations move through the air, floors, ceilings and walls. The sound waves move from one room to the other, or from the outside of the home to inside. This includes traffic noise or the sound of noisy neighbors. Insulation is a good sound absorber and is effective at minimizing the noises entering a room.
Soundproofing consists of using a barrier of some sort to prevent sound from entering the space that has been sound proofed. There are two basic ways to achieve this reduction in sound: noise absorption and noise reduction.
Approaches to Sound Insulation
There are a few approaches to noise level reduction or noise absorption. A variety of materials can be used for either purpose. Noise reduction can be accomplished with the use of space between rooms. The more space, the more room for sound waves to dissipate. If you increase the distance between the source of the noise and the space, you will reduce the noise that enters the space.
The other method, noise absorption, is also referred to as dampening. With this method, the sound waves are converted to heat within the insulation. This increases energy efficiency, while reducing sound. It also suppresses the echoes and reverberation of sound waves.
NRC: The Basics
- The NRC rating for sound absorption materials ranges from 0 (perfectly reflective) to 1 (perfectly absorptive)
- It is an average of how absorptive a material is at four different frequencies (250, 500, 1000, and 2000)
- Because the rating is an average, two materials with the same rating might not perform the same at all frequencies and in all applications
- The NRC can also be viewed as the percentage of sound waves which come into contact with the sound absorption material that are not reflected back within the space. Example: NRC of .5=50%
- Different materials with the same NRC may provide very different results. Performance at different frequencies may be very different
- The NRC rating does NOT measure how well a material can block sound
- Depending on a material’s shape and surface area, some acoustic soundproofing products can test at an NRC above 1
SOUND BLOCKING with sound insulation material stops sound from entering or leaving a room. Sound insulation material is perfect for blocking loud music, voices, traffic, and many other distractions. Look for sound blocking materials with a high Sound Transmission Class (STC) rating. This number, the higher the better, indicates how effective a certain sound insulation material is at sound blocking. For instance, sound insulation material with a 35 STC would block most normal speech while material with a rating of 60 would render most sounds inaudible.
STC is roughly the decibel reduction in noise a material/partition can provide, abbreviated ‘dB’. The human ear perceives a 10dB reduction in sound as roughly reducing the volume by half. For example, a sound reduction from 50dB to 40dB seems half as loud. This is an important fact to keep in mind when considering a sound solution that ‘fits’ the problem. To understand how to soundproof a wall to create a higher STC rating
Common STC Ratings
A common acoustic issue in virtually any space is sound transmission. Sound transmission can be both airborne and/or structure borne vibration. (Structure borne vibration is assessed by a different standard, Impact Insulation Class – IIC, and is not addressed in this text). Airborne sound travels through the air and can transmit through a material, assembly or partition. Sound can also pass under doorways, through ventilation, over, under, around, and through obstructions. When sound reaches a room where it is unwanted, it becomes noise. Noise such as that from automobiles, trains and airplanes can transmit through the exterior structure of a building. In the same way, noise from mechanical equipment or speech can transmit from one room within a building to an adjacent space.
Sound transmission can cause noise control, confidentiality, and privacy issues. Sound from a noisy environment such as a mechanical equipment room or an area with loud activities or music can transmit through a partition into a quieter space. This will cause unwanted noise within the quieter space. This is not only an annoyance; in several cases it can cause the quieter space to become unusable for its intended purpose. Several spaces require confidentiality. Offices of counselors, lawyers, or human resource departments cannot function in a space where sound will transmit through the surrounding walls and into an adjacent space. In most other office situations if confidentiality is not an issue, privacy is. If sound transmission is not properly controlled, the space or environment will not provide privacy for its users.
- When soundproofing rooms, the STC of your doors & windows need to be equal to or greater
than the STC of your walls in order to maximize the rating.
- Structurally decoupling drywall panels from each other (using steel studs, a staggered-stud wall, double wall stud, or resilient channels) can produce an STC rating as high as 63 (for a double stud wall) and will result in effective low-frequency loss. This when compared to a normal wall with an STC of 33, will make most frequencies inaudible, making the room sound 88 percent quieter.
- Music-related sounds may require the highest STC ratings. In practical terms, a 55 STC rating will prevent a resident living in a multi-family home from being bothered at all by their neighbor’s loud music.