# Noise control ## Overview Techniques for reducing unwanted sound in buildings and industrial environments. **Noise control** is the discipline of reducing unwanted sound (noise) by acting on any of three links in the chain between a sound and a listener: the source that generates it, the path it travels, and the receiver who hears it. It is broader than [[Soundproofing]], which works mainly on the path between two spaces; noise control also redesigns machines to make less noise in the first place, and protects or relocates the people who would otherwise hear it. The distinction matters in practice — regulators, engineers and building codes all organize noise-control measures the same way, as source treatments, path treatments and receiver treatments, a framework detailed below under Approaches to noise control. The microsim built for this article, *Noise control: a barrier's shadow and active cancellation*, sets both a path measure and a receiver measure side by side. On the left, raising a barrier between a source and a receiver casts an acoustic shadow whose depth depends on how many half-wavelengths longer the path over the barrier's top edge is than the direct path — the diffraction problem that governs every highway sound wall and warehouse partition. On the right, an active-noise-control system tries to cancel the sound reaching the receiver directly with an antiphase copy, and the sim shows how quickly that cancellation collapses as the antiphase wave's timing or level drifts off from exact. *Try: raise the barrier height and watch the shadow deepen behind it, then lower the frequency and watch how a long wavelength bends around the same barrier almost unhindered; separately, dial in an ANC phase error and gain error and watch the residual noise curve grow as the antinoise stops canceling.* ## Acoustics bridge Barn ventilation, implement cab damping ## Hub connections ### Engineering Center of Excellence Secondary acoustic application context (to be developed). ### Advanced Manufacturing Center of Excellence Secondary acoustic application context (to be developed). ### Transportation Center of Excellence Secondary acoustic application context (to be developed). ### Energy Center of Excellence Secondary acoustic application context (to be developed). ### IT Center of Excellence Secondary acoustic application context (to be developed). ### HealthForce Center of Excellence Secondary acoustic application context (to be developed). ### Northern Agricultural Center of Excellence Secondary acoustic application context (to be developed). ### Southern Agricultural Center of Excellence (primary) This article bridges [[PORTAL_Acoustics]] to the [[WT!Southern_Agricultural_Center_of_Excellence]]. The acoustic signature of noise control is central to southern agricultural operations. ### Space Mining In Minnesota — Center Circle Secondary acoustic application context (to be developed). ## Standards, recommendations, and guidelines Noise control is unusual among acoustics topics in being extensively regulated, because occupational and environmental noise exposure has a dose–response relationship with hearing damage that regulators can write directly into exposure limits. ### Occupational Safety and Health Administration (OSHA) OSHA's general industry noise standard, 29 CFR 1910.95, sets a permissible exposure limit of 90 [[Decibel|dBA]] averaged over an 8-hour day, with hearing-conservation measures — monitoring, protection, audiometric testing — required once exposure reaches an 85 dBA action level; the standard uses a 5 dB exchange rate, so each 5 dB increase in level halves the exposure duration allowed.[^osha] ### Mine Safety and Health Organization (MSHA) The Mine Safety and Health Administration applies a parallel standard, 30 CFR Part 62, to underground and surface mining, with the same 90 dBA permissible exposure limit, 85 dBA action level and 5 dB exchange rate as OSHA's general industry rule, reflecting the historically high noise exposure of mining equipment.[^msha] ### Federal Railroad Administration (FRA) The FRA's occupational noise rule for railroad workers, 49 CFR Part 227, likewise sets a 90 dBA time-weighted average permissible exposure limit and an 85 dBA action level with a 5 dB exchange rate, alongside a hard 115 dBA ceiling that may never be exceeded regardless of duration.[^fra] ### U.S. Department of Defense The Department of Defense's Hearing Conservation Program, DoDI 6055.12, instead follows the stricter 3 dB exchange rate the National Institute for Occupational Safety and Health recommends, with an 85 dBA action level — a more conservative standard than OSHA's civilian 5 dB rate, reflecting sustained high-noise exposure in military settings from flight decks to firing ranges.[^dod] ### European Parliament and Council Directive The European Union's Directive 2003/10/EC on the minimum health and safety requirements for exposure of workers to the risks from noise sets three thresholds rather than one: a lower exposure action value of 80 dB(A), an upper exposure action value of 85 dB(A) that triggers mandatory hearing protection, and an exposure limit value of 87 dB(A), measured after any hearing protection worn, that may never be exceeded.[^eu] ## Approaches to noise control ### Sources Source treatment reduces the [[Sound|sound]] a machine, vehicle or process generates in the first place — a quieter gear profile, a balanced rotating part, a muffler on an engine's exhaust, or simply specifying quieter equipment during purchasing. It is usually the most effective and the most expensive point in the chain to intervene, because it removes acoustic energy before it can radiate or travel at all. ### Path Path treatment works on the route sound takes between source and receiver: absorption, mass-law barriers of the kind detailed in [[Soundproofing]], and free-standing noise barriers of the kind modeled in this article's microsim. A barrier attenuates sound by forcing it to diffract over (or around) its top edge; the added path length, measured in half-wavelengths as the Fresnel number N = 2δ/λ, sets the depth of the acoustic shadow behind it. Maekawa's empirical formula for a thin, semi-infinite barrier gives the attenuation as A = 5 + 20 log₁₀(√(2πN)/tanh√(2πN)) dB, capped near 24 dB in practice; a 3 m barrier standing between a source and a receiver 9 m beyond it, at a 500 [[Frequency|Hz]] test tone, works out to N ≈ 2.3 and about 16.5 dB of attenuation.[^maekawa1968] Long wavelengths — low frequencies — diffract around a barrier far more readily than short ones, which is why a highway noise wall is much better at quieting tire hiss than the low rumble of a diesel engine. ### Receiver Receiver treatment protects or relocates the person hearing the noise rather than the source or the path: hearing protectors, enclosed operator cabs, or simply standing farther away. [[Active_noise_control|Active noise control]] is a receiver-side technique that cancels sound electronically rather than blocking it mechanically: a circuit adds an antiphase copy of the incoming noise, and because sound pressures from different sources add algebraically, the sum can be reduced by 30 dB or more under favorable conditions.[^upv1-anc] The cancellation is fragile: for a phase error φ and a gain error e in the antinoise signal, the residual noise left over scales with |1 − (1 + e)·e^(iφ)|², so a 10-degree phase error and a 5 percent gain error already leave the noise only about 15 dB down rather than 30, and a phase error past 60 degrees can leave the antinoise adding to the noise instead of canceling it.[^ancresidual] ## Basic technologies The technologies built on the source–path–receiver framework are largely the same ones detailed under [[Soundproofing]] — absorption, mass, damping, decoupling, distance and diffusion for passive path treatments, and active cancellation for receiver treatment — applied here to whole environments (a factory floor, a roadway corridor, an airport) rather than to a single wall or room. ## Roadways Highway traffic noise in the United States is regulated under the Federal Highway Administration's Noise Abatement Criteria, 23 CFR Part 772, which sets a threshold — commonly cited as 67 dBA on the hourly equivalent sound level, Leq(h), for residential land use — above which a federally funded highway project must evaluate noise-abatement measures such as barriers, and a barrier is generally considered reasonable and feasible only if it can achieve at least 5 dB of attenuation for the benefited residences.[^fhwa] A traffic noise wall works by the same barrier diffraction physics modeled in this article's microsim, applied at highway scale. ## Aircraft ### Acoustic liners Modern turbofan engines line the inside of their intake and bypass ducts with acoustic liners — perforated or micro-slotted face sheets bonded over a honeycomb core of small resonant cavities — that act as an array of tuned Helmholtz resonators absorbing fan and turbomachinery noise before it can radiate from the duct; engine and aircraft noise certification limits, set out in 14 CFR Part 36 in the United States (and the corresponding ICAO Annex 16 standards internationally), have driven the fitting of ever more effective liners as aircraft noise limits have tightened over successive certification stages.[^faa14cfr36] ## Architectural solutions Inside a building, noise control uses absorptive ceiling and wall finishes to lower the reverberant buildup described in [[Reverberation]], sound-masking systems that raise the ambient background just enough to cover distracting speech and equipment noise, and layout choices — placing noisy mechanical rooms and quiet occupied spaces as far apart as the building allows — that lean on the same distance and path measures covered under Approaches to noise control above. ## Post-architectural solutions ### Industrial Industrial noise control follows a hierarchy of controls: engineering measures at the source or path are preferred over administrative measures (rotating workers to limit individual exposure time) and personal protective equipment (earplugs or earmuffs) is treated as the last line of defense precisely because it protects only the wearer and only when worn correctly and consistently, the same logic embodied in the OSHA and MSHA hearing-conservation standards cited above. ### Commercial Offices and other commercial spaces apply the same tools at a gentler scale: acoustic ceiling tile, partial-height partitions backed by absorptive infill, and duct silencers on shared HVAC systems, mirroring the residential and commercial applications described in [[Soundproofing]]. ### Residential Residential noise control covers appliance and HVAC equipment noise, party-wall and floor treatments already detailed under [[Soundproofing]], and, in the United States, a now-largely-dormant regulatory history: the Noise Control Act of 1972 created an EPA Office of Noise Abatement and Control that set noise-emission standards for products such as trucks and air compressors, but the office lost its funding in 1982 and most direct federal noise regulation since then has been left to state and local governments.[^epa-onac] ## Urban planning Urban and land-use planning treats [[Noise_pollution|noise]] as a factor in where people should and should not live, work, or be exposed for long periods: zoning that buffers residential areas from highways, rail corridors and airports with distance or intervening land use, and, in the European Union, a requirement under the Environmental Noise Directive (2002/49/EC) that every agglomeration above 100,000 residents produce strategic noise maps and action plans for road, rail, air and industrial noise.[^eu-envnoise] ## Minnesota *This section is specific to Wikitube.* The Metropolitan Airports Commission, which operates Minneapolis–Saint Paul International Airport, runs one of the country's longer-running residential sound-insulation programs, retrofitting homes in the airport's noise-affected corridor with upgraded windows, doors and ventilation under a Part 150 noise-compatibility program coordinated with the Federal Aviation Administration — a receiver-side noise-control measure applied at the scale of an entire metropolitan area rather than a single building.[^mac] ## See also - [[Soundproofing]] - [[Reverberation]] - `Active_noise_control` · `Noise_pollution` — not yet on Wikitube (forward references) ## References [^osha]: U.S. Occupational Safety and Health Administration, 29 CFR 1910.95, "Occupational noise exposure." https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.95 [^msha]: U.S. Mine Safety and Health Administration, 30 CFR Part 62, "Occupational Noise Exposure." https://www.msha.gov/regulations/rules [^fra]: U.S. Federal Railroad Administration, 49 CFR Part 227, "Occupational Noise Exposure for Railroad Operating Employees." https://www.fra.dot.gov/ [^dod]: U.S. Department of Defense, DoDI 6055.12, "Hearing Conservation Program (HCP)," applying the NIOSH-recommended 3 dB exchange rate. https://www.cdc.gov/niosh/docs/98-126/ [^eu]: Directive 2003/10/EC of the European Parliament and of the Council on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise). https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32003L0010 [^maekawa1968]: Maekawa, Zyun-iti (1968). "Noise reduction by screens." *Applied Acoustics* 1 (3): 157–173. *(DOI not independently verified for this article.)* [^upv1-anc]: OpenStax, *University Physics Volume 1* (2016), §17.3 "Sound Intensity," subsection "Noise Reduction through Destructive Interference" and Figure 17.18 (the "30 dB or more" active-cancellation figure and the 1986 Voyager aircraft headsets). https://openstax.org/details/books/university-physics-volume-1 [^ancresidual]: The residual-noise formula |1 − (1 + e)·e^(iφ)|² for an active-noise-control system with gain error e and phase error φ, and the barrier attenuation and Fresnel-number formulas above, are the equations built into this article's microsim (`specs/acoustics/sims/Noise_control.json`); the barrier and cancellation physics follow Maekawa (1968) and the superposition principle in OpenStax §16.5/17.3 respectively. [^fhwa]: U.S. Federal Highway Administration, 23 CFR Part 772, "Procedures for Abatement of Highway Traffic Noise and Construction Noise" (Noise Abatement Criteria). https://www.fhwa.dot.gov/environment/noise/ [^faa14cfr36]: U.S. Federal Aviation Administration, 14 CFR Part 36, "Noise Standards: Aircraft Type and Airworthiness Certification." *Citation needed: the specific historical progression of certification "Stage" noise limits was not independently re-verified for this article.* https://www.faa.gov/ [^epa-onac]: U.S. Environmental Protection Agency, Noise Control Act of 1972 (Public Law 92-574) and the history of the Office of Noise Abatement and Control, defunded in 1982. https://www.epa.gov/clean-air-act-overview/noise-pollution [^eu-envnoise]: Directive 2002/49/EC of the European Parliament and of the Council relating to the assessment and management of environmental noise (the Environmental Noise Directive). https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32002L0049 [^mac]: Metropolitan Airports Commission, "Residential Sound Insulation Program," Minneapolis–Saint Paul International Airport. https://www.metroairport.org/ ## External links - [OSHA Occupational Noise Exposure](https://www.osha.gov/noise), U.S. Department of Labor - [Environmental Noise Directive](https://environment.ec.europa.eu/topics/noise_en), European Commission <!-- ACOUSIM:BEGIN g22 — Acoustics portal microsim (framework build, specs/acoustics/sims/Noise_control.json); do not hand-edit inside --> **Microsim — three.js (Wikitube framework):** *Noise control* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/acoustics/Noise_control.html" data-title="Noise control"></div> *Built from `MICROSIM_GUIDE/specs/acoustics/sims/Noise_control.json`; part of the [[PORTAL_Acoustics|Acoustics portal]] spine (section sims and See-also variants).* <!-- ACOUSIM:END --> ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Noise_control) : [Wikitube](https://en.wikitube.io/wiki/Noise_control) - skeleton pinned to revision 1359043159 (2026-09-11). <!-- hub tags: GENERATIVE; Centers_of_Excellence; PORTAL_Acoustics section 19 --> --- *Bridge article, scaffolded from [[PORTAL_Acoustics]]. Minimal content; awaiting expansion.*