Soundproofing
Soundproofing is any means of impeding sound propagation. There are several basic ways to reduce sound: increasing the distance between source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles for absorption, or using active antinoise sound generators.[1][2]
Acoustic quieting and noise control can be used to limit unwanted noise. Soundproofing can reduce the transmission of unwanted direct sound waves from the source to an involuntary listener through the use of distance and intervening objects in the sound path (see sound transmission class and sound reduction index).
Soundproofing can suppress unwanted indirect sound waves such as reflections that cause echoes and resonances that cause reverberation.
Damping[edit]
Damping serves to reduce resonance in the room, by absorption or redirection through reflection or diffusion. Absorption reduces the overall sound level, whereas redirection makes unwanted sound harmless or even beneficial by reducing coherence. Damping can be separately applied to reduce the acoustic resonance in the air or to reduce mechanical resonance in the structure of the room itself or things in the room.
Decoupling[edit]
Creating separation between a sound source and any form of adjoining mass, hindering the direct pathway for sound transfer.
Distance[edit]
The energy density of sound waves decreases as they become farther apart so increasing the distance between the receiver and source results in a progressively lesser intensity of sound at the receiver. In a normal three-dimensional setting, with a point source and point receptor, the intensity of sound waves will be attenuated according to the inverse square of the distance from the source.
Mass[edit]
Adding dense material to treatment helps stop sound waves from exiting a source wall, ceiling or floor. Materials include mass-loaded vinyl, drywall, soundproof sheetrock, plywood, fibreboard, concrete or rubber. Different widths and densities in soundproofing material reduce sound within a variable frequency range.
Reflection[edit]
When sound waves hit a medium, the reflection of that sound is dependent on the dissimilarity of the material it comes in contact with.[7] Sound hitting a concrete surface will result in a much different reflection than if the sound were to hit a softer medium such as fiberglass. In an outdoor environment such as highway engineering, embankments or paneling are often used to reflect sound upwards into the sky.
Diffusion[edit]
If a specular reflection from a hard flat surface is giving a problematic echo then an acoustic diffuser may be applied to the surface. It will scatter sound in all directions.
Active noise control[edit]
In active noise control, a microphone is used to pick up the sound that is then analyzed by a computer; then, sound waves with opposite polarity (180° phase at all frequencies) are output through a speaker, causing destructive interference and canceling much of the noise.
Residential[edit]
Residential sound programs aim to decrease or eliminate the effects of exterior noise. The main focus of the residential sound program in existing structures is the windows and doors. Solid wood doors are a better sound barrier than hollow doors.[8] Curtains can be used to dampen sound, either through use of heavy materials or through the use of air chambers known as honeycombs. Single-, double- and triple-honeycomb designs achieve relatively greater degrees of sound damping. The primary soundproofing limit of curtains is the lack of a seal at the edge of the curtain, although this may be alleviated with the use of sealing features, such as hook and loop fastener, adhesive, magnets, or other materials. The thickness of glass will play a role when diagnosing sound leakage. Double-pane windows achieve somewhat greater sound damping than single-pane windows when well-sealed into the opening of the window frame and wall.[9]
Significant noise reduction can also be achieved by installing a second interior window. In this case, the exterior window remains in place while a slider or hung window is installed within the same wall openings.[10]
In the US, the FAA offers sound-reducing for homes that fall within a noise contour where the average sound level is 65 dB SPL or greater. It is part of their Residential Sound Insulation Program. The program provides solid-core wood entry doors plus windows and storm doors.[11]
Walls[edit]
Mass is the only way to stop sound. Mass refers to drywall, plywood or concrete. Mass-loaded vinyl (MLV) is used to dampen or weaken sound waves between layers of mass. Use of a viscoelastic damping compound[13] or MLV converts sound waves into heat, weakening the waves before they reach the next layer of mass. It is important to use multiple layers of mass, in different widths and density, to optimize any given soundproofing treatment.[14] Installing soundproof drywall is recommended for its higher sound transmission class (STC) value. Soundproof drywall in combination with a viscoelastic compound may achieve a noise reduction of STC 60+.
Walls are filled with mineral wool insulation. Depending on the desired level of treatment, two layers of insulation may be required. Outlets, light switches, and electrical boxes are weak points in any given soundproofing treatment. Electrical boxes should be wrapped in clay or putty and backed with MLV. After switch plates, outlet covers and lights are installed, acoustical caulking should be applied around the perimeter of the plates or fixtures.
Commercial[edit]
Restaurants, schools, office businesses, and healthcare facilities use architectural acoustics to reduce noise for their customers. In the United States, OSHA has requirements regulating the length of exposure of workers to certain levels of noise.[15]
For educators and students, improving the sound quality of an environment will subsequently improve student learning, concentration, and teacher-student inter-communications. In 2014, a research study conducted by Applied Science revealed 86% of students perceived their instructors more intelligibly, while 66% of students reported experiencing higher concentration levels after sound-absorbing materials were incorporated into the classroom.[16]