Editing Soundproofing (section)

== Techniques ==

===Absorption===
Sound-absorbing material controls reverberant sound pressure levels within a cavity, enclosure or room. Synthetic absorption materials are porous, referring to [[open cell foam]] (acoustic foam, soundproof foam).<ref>{{cite web |title=Acoustic foam: a method to achieve acoustic |publisher=Tabnak |url=https://www.tabnak.ir/005C6J}}</ref> Fibrous absorption material such as cellulose, mineral wool, fiberglass, sheep's wool, are more commonly used to deaden resonant frequencies within a cavity (wall, floor, or ceiling insulation), serving a dual purpose along with their [[thermal insulation]] properties. Both fibrous and porous absorption material are used to create [[acoustic panel]]s, which absorb sound reflections in a room, improving speech intelligibility.<ref>{{Cite thesis |last=Ghaffari Mosanenzadeh |first=Shahrzad |title=Design, characterization and modeling of biobased acoustic foams |date=2014 |degree=PhD |publisher=University of Toronto |hdl=1807/71305 |hdl-access=free |bibcode=2014PhDT.......199G}}</ref><ref>{{Cite journal |last1=Kulakov |first1=Kirill |last2=Romanovich |first2=Marina |date=2019 |title=Technical comparison of soundproof wall panels |url=https://www.e3s-conferences.org/articles/e3sconf/pdf/2019/17/e3sconf_tpacee2019_02027.pdf |journal=E3S Web of Conferences |volume=91 |pages=2, 4, 5 |doi=10.1051/e3sconf/20199102027 |doi-access=free}}</ref>

====Porous absorbers====
Porous absorbers, typically open cell [[rubber]] foams or [[Melamine foam|melamine sponges]], absorb noise by friction within the cell structure.<ref>{{Cite book |last1=Cox |first1=Trevor J. |url=https://books.google.com/books?id=f19_6NFg4jkC&q=Acoustic+absorbers+and+diffusers:+theory,+design+and+application |title=Acoustic Absorbers and Diffusers |last2=D'Antonio |first2=Peter |date=2009 |publisher=CRC Press |isbn=9780203893050}}</ref> Porous open cell foams are highly effective noise absorbers across a broad range of medium-high frequencies. Performance can be less impressive at lower frequencies. The exact absorption profile of a porous open-cell foam will be determined by a number of factors including cell size, [[tortuosity]], porosity, thickness, and density. 

The absorption aspect in soundproofing should not be confused with sound-absorbing panels used in acoustic treatments. Absorption in this sense refers to reducing a resonating frequency in a cavity by installing insulation between walls, ceilings or floors. Acoustic panels can play a role in treatment reducing reflections that make the overall sound in the source room louder, after walls, ceilings, and floors have been soundproofed.

====Resonant absorbers====
Resonant panels, [[Helmholtz resonator]]s and other resonant absorbers work by damping a sound wave as they reflect it.<ref>{{cite web|url=http://www.studiotips.com/acoustics.html|title=Low frequency absorption|publisher=Studio tips|archive-url=https://web.archive.org/web/20190807040528/http://www.studiotips.com/acoustics.html|archive-date=2019-08-07}}</ref> Unlike porous absorbers, resonant absorbers are most effective at low-medium frequencies and the absorption of resonant absorbers is matched to a narrow frequency range.

===Damping===
[[Damping]] serves to reduce [[Room modes|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 [[Temporal coherence|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===
Creating separation between a sound source and any form of adjoining mass, hindering the direct pathway for sound transfer.

===Distance===
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===
Adding dense material to treatment helps stop sound waves from exiting a source wall, ceiling or floor. Materials include mass-loaded vinyl, soundproof sheetrock or drywall, plywood, [[Medium-density fibreboard|fibreboard]], concrete or rubber. Different widths and densities in soundproofing material reduce sound within a variable frequency range.

===Reflection===
When sound waves hit a medium, the reflection of that sound is dependent on the dissimilarity of the material it comes in contact with.<ref>{{Cite web|url=http://www.physicsclassroom.com/class/sound/Lesson-3/Reflection,-Refraction,-and-Diffraction|title=Reflection, Refraction, and Diffraction|website=www.physicsclassroom.com|access-date=2017-07-10}}</ref> 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===
If a [[specular reflection]] from a hard flat surface is giving a problematic echo then an [[Diffusion (acoustics)|acoustic diffuser]] may be applied to the surface. It will scatter sound in all directions.

===Active noise control===
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.