Noise is the data centre impact neighbours actually live with, yet most consent conditions measure it in units that cannot hear the problem. The fan makers have delivered real innovation, the unit makers offer quiet versions of everything and the hardest bands of the sound spectrum remain wide open. For assessors, the fix starts with what gets measured.
Why this matters
Noise is the impact neighbours live with daily, yet a data centre can comply with conventional noise limits while still producing the low-frequency hum communities find most intrusive, because standard measurements do not capture it directly. The fix starts with measuring in the right units. Communities, councils and operators all benefit when limits can actually hear the problem.
When Chandler, Arizona voted down a data centre proposal, noise was central to the objection. Across Northern Virginia, the densest data centre market on earth, residents describe a hum that follows them indoors, while compliance reports insist the facilities are within their limits. Both things are true at once and the reason is the unit of measurement. Most noise conditions are written in A-weighted decibels, a scale designed around the sensitivity of human hearing to mid and high frequencies. Cooling plant emits much of its energy below 200 hertz, where A-weighting discounts it steeply. A facility can meet an LAeq limit precisely while at the same time producing the low-frequency drone that generates every complaint. The difference between C-weighted and A-weighted sound levels (dBC–dBA) is widely used as a screening indicator for low-frequency noise. When the difference approaches or exceeds about 15 decibels, it suggests that low-frequency energy is becoming a significant part of the sound and that A-weighted measurements alone may not fully represent the low-frequency character experienced by nearby residents.
Three problems, not one
Data centre cooling noise is three distinct problems that are typically lumped together under one name. Broadband fan noise across the mid and high frequencies is largely solved using a combination of distance, orientation, acoustic barriers, louvres and shrouds delivering 5 to 15 decibels of attenuation at known cost. Tonal noise is harder: dozens of fans running at similar speeds produce energy concentrated at the blade-pass frequency and its harmonics; near-identical tones then beat against each other to create the wandering, pulsing character that people find disproportionately annoying at modest measured levels. The genuinely unsolved problem is the low-frequency band from 20 to 200 hertz, where wavelengths run from 1.7 to 17 metres. Sound at that scale diffracts over barriers, carries for kilometres, passes through standard housing construction and excites the room resonances that turn a distant plant item into a bedroom problem.
Below all of that sits infrasound, the energy under 20 hertz that is felt rather than heard: pressure sensations, rattling windows and the sense of a presence nobody can point to. Data centres genuinely produce it, mostly from large slow fans whose blade-pass frequencies can fall into the teens of hertz and from generator exhausts under test. The honest science: measured infrasound levels near well-designed facilities generally sit below human perception thresholds and the direct-harm evidence is weak, but the secondary effects are real, because building elements rattle at these frequencies and the rattle is audible even when the source is not. Infrasound also travels furthest of all and no barrier touches it, so the fixes live at the source: fan selections that keep blade-pass frequencies above the band, vibration isolation on the structure-borne paths that dominate down here and exhaust silencing on the generator side. Measurement has its own convention, G-weighting under ISO 7196 plus unweighted third-octave data below 20 hertz; modern monitors log it cheaply, which removes the last excuse for not looking. One development suits this band unusually well: active noise control, marginal outdoors at mid frequencies, works best against long coherent low-frequency waves in confined paths such as ducts and exhausts, which is where the emerging products aim.
What the manufacturers have actually done
The most substantial innovation sits a tier below the brands on the equipment schedule. The axial fans inside most branded cooling units come from specialist makers and the leaders have spent two decades on aeroacoustics. Ziehl-Abegg’s owlet series is the emblem: sickle-shaped blades with serrated trailing edges copied from the barn owl’s wing and a rippled leading edge in the latest generation, claiming up to 12 decibels of improvement over its predecessors, in many cases removing the need for separate silencers. ebm-papst’s equivalents follow the same logic. Because noise falls steeply as blade speed drops, the other quiet revolution is simply diameter: bigger, slower fans moving the same air.
The unit makers integrate this work into tiered offerings. Stulz builds its low-noise chillers around oversized 910 millimetre fans, encapsulated compressors and redesigned internal airflow. Vertiv’s Liebert chiller ranges ship in standard, low-noise and quiet versions with EC fans and acoustic insulation. Schneider’s Uniflair line offers the same laddered configurations. The operational lever matters as much as the hardware: EC fans obey the fan laws, so a facility willing to raise its chilled water temperature overnight can slow its fans and shed several decibels exactly when limits tighten and backgrounds fall. Free cooling reduces compressor hours. Liquid and immersion cooling remove the server-level fans but the heat still leaves the site through outdoor plant, so the fence-line question relocates rather than disappears.
The honest summary is that manufacturers compete hard on the A-weighted sound power of a single unit and that competition has worked. Nobody yet sells the thing communities need: a site that remains genuinely quiet at the property boundary, not simply a collection of individually quiet components.
The open ground
Three gaps stand out, all of them live territory for innovation.
The first is passive low-frequency control. Conventional splitter attenuators create back-pressure, which forces fans to run faster, which makes more noise: a genuinely vicious loop. Ventilated acoustic metamaterials break the loop in the laboratory, using arrays of Helmholtz resonators and tuned membranes to deliver around 10 decibels of insertion loss in the 100 to 200 hertz band while letting air pass. At the time of writing, they are not yet commercialised at data centre scale.
The second is tonal management across the fan array. The beating hum is an interaction effect between dozens of similar fans, which means it can be attacked in software: coordinated speed control that deliberately spreads blade-pass frequencies so tones neither align nor beat. The control hardware already exists in every EC fan on site. Specialist consultancies have also shown that small aerodynamic retrofits can remove specific tones at source for a fraction of the cost of enclosure. Both approaches remain boutique solutions.
The third is measurement itself. Continuous, community-visible noise monitoring with C-weighted and third-octave data published alongside the A-weighted compliance figure would move most disputes from assertion to evidence. The technology is ordinary; the practice is rare.
What an assessor should require
The assessment fixes follow directly. Write limits that can hear the problem: an A-weighted limit alone is not adequate for plant of this character, so add a C-weighted or third-octave low-frequency criterion and a tonality penalty of the kind long standard in the UK’s rating method, with G-weighted infrasound measurement where large fan or generator installations sit near homes. Require the night-mode question to be answered in the application: what do the fans do between 10pm and 7am and what water temperature supports it? Make continuous monitoring with published data a condition rather than a complaint response. Ask how the fan array is managed as an array, not as a catalogue of individually compliant units. Require the plant schedule to state the acoustic tier actually purchased, because every major manufacturer sells a quieter version of the same unit and the delta is a procurement decision made years before anyone complains.
The bottom line
Data centre noise is not an unsolvable problem; it is a mismeasured one with a thin market for the hardest fixes. The fan makers have done their part and the unit makers will sell quiet to anyone who specifies it. What remains open is the low-frequency band, the site-level soundscape and the verification gap; the first movers in each will find communities, councils and operators equally motivated. In the meantime, a regime that measures only in A-weighted decibels risks overlooking the part of the spectrum that communities most often identify as problematic.
A topical commentary from the Digital Infrastructure Institute. For plain-English community information on data centre noise, see our community information series; for assessment practice, our State & Territory Frameworks.
Sources: Chandler City Council vote (Dec 2025); EESI — communities raising noise pollution concerns; WUSA9 — the Northern Virginia hum; Ziehl-Abegg — biomimetic fan concepts; AskNature — owl-wing fan design; Noise Monitoring Services — data centre noise control and dBC–dBA screening; ISO 7196:1995 (infrasound G-weighting)