Noise & siting

Communities live with a lot of sound already: freight trains, highways, factories and, in a college town, game days. Lawrence has all of them. The Union Pacific line through North Lawrence sounds its horns at downtown crossings (City of Lawrence), and a home football crowd fills the stadium on fall Saturdays. Putting data-center sound beside those familiar sources shows its scale.

Sound	Level	Where it is measured
Train horn (federal requirement)	96–110 dBA	100 feet ahead of the locomotive (FRA)
College football crowd	109–114 dB (loudest 10 seconds)	Inside the stadium (Penn State)
Diesel truck	90 dBA	50 feet away (Illinois DOT)
General freight train	About 85 dBA	100 feet away (Illinois DOT)
Conversation	About 60 dBA	Three feet away (JLARC)
Heavy traffic	About 60 dBA	300 feet away (Illinois DOT)
Overland Park, Kansas residential limit	60 dBA day, 55 dBA night	Off the source's property (ordinance)
Virginia locations measured after data-center complaints	40–59 dBA	Total sound at the complaint measurement locations (JLARC)

Even the readings Virginia took where neighbors had complained came in below a normal conversation. Virginia's legislative auditors identified at least 15, or about 10% of Virginia's operational sites, with reported noise problems, and found that most data centers sit in industrial or commercial areas away from homes. They also describe the smaller facilities common a decade earlier as similar in size and appearance to commercial office buildings (JLARC). A facility's scale, equipment and setting shape what neighbors see and hear.

Equipment placement, cooling design and buildings also influence what neighbors hear. Engineers can examine those choices while a project is still on paper, using sound models to compare designs before construction.

Fairfax County's September 2024 amendment provides a concrete example. Its framework combines equipment enclosures or barriers with sound studies before site-plan approval and after construction. That connects a design decision to a later check of the installed equipment.

Start with equipment and its operating schedule

Data centers use industrial cooling equipment to carry heat away from servers. Fans, chillers and other components can produce sound during normal operation. Backup generators have a different schedule: they run for testing, maintenance and power outages. When they run, they are a separate, intermittent sound source, not the routine source of the continuous cooling hum. JLARC describes generator use as limited, with most operators reporting only short, infrequent outages and otherwise running them for maintenance.

Construction is another phase, with grading, building work, equipment installation and deliveries. A construction schedule explains when that work happens; the operating plan explains what continues once the building opens.

These are different sound sources. A study that describes ordinary cooling operation answers a different question from a generator test or a busy construction day. Identifying the equipment and schedule makes the discussion specific.

Fairfax's Fall 2024 guidance makes that distinction explicit. It treats emergency generator use and qualifying daytime testing as exempt from the study. Routine testing qualifies when it occurs between 7 a.m. and 9 p.m. and totals no more than two hours in a day; other testing must be included. Those are the county guidance's categories, not a rule for every locality.

Use the layout to shape what neighbors hear

A site plan shows more than the building footprint. The locations of cooling equipment, generators, homes and other nearby uses matter, along with the direction sound travels and the effect of intervening buildings and terrain.

JLARC explains that a facility's design and cooling system affect whether sound can be heard beyond its property line. Geography and surrounding buildings also affect its travel. Its recommendations favor choosing suitable locations and examining sound before construction.

Fairfax's adopted framework requires operating equipment to be enclosed unless the director determines that enclosure is mechanically infeasible from manufacturer specifications. In that case, a wall or similar barrier is required. The standards also address the separation of buildings and ground-level equipment from residential properties, with alternatives available through special-exception approval.

This gives designers several connected choices: equipment location, enclosure, screening and the building's position. The acoustic analysis can test how those choices work together. A setback is space; the sound model explains what the equipment is expected to produce at nearby locations.

Model the whole project, then measure it

Fairfax's noise-study guidance calls for an engineer with acoustic expertise. The model considers sound-source location and direction, buildings and topography.

For the development covered by the lot or site plan, it must address both the proposed phase and the ultimate buildout at full occupancy. It also considers maximum sound output with cooling and other non-exempt noise-generating equipment operating simultaneously at full load.

That is useful information before approval. It lets the design team and reviewers examine the completed project's operating conditions, rather than considering only the first building or a lightly loaded facility.

The next step is measurement. Before issuance of a Nonresidential Use Permit, the guidance requires a post-construction study with field measurements of installed equipment. Where future equipment is planned, those measurements should calibrate the model used to analyze the existing and planned installation together.

A model predicts; a field study measures. Keeping both in the public record lets residents and officials follow the project from its design assumptions to its built condition.

What the comparisons measure

The train and truck examples are substantially louder than the levels in JLARC's complaint-related records. The distances are part of that comparison: sound at a nearby machine is different from sound reaching a home farther away. The Virginia readings captured total sound, not the data-center contribution isolated from other sources, and the locations were selected because of complaints.

The next comparison is with the sound already present at the actual site. JLARC describes establishing that baseline before construction so later measurements can show what a facility adds. Where road or industrial sound is already present, a facility's sound adds to that existing level, and a baseline measurement shows by how much. The same equipment is easier to hear where the background is quiet, particularly at night.

A passing train rises and falls; cooling equipment can run continuously. A factory may operate particular shifts; a generator test has a schedule. Comparing the loudest moment, the duration and the quieter intervals gives those familiar examples meaning. The Illinois guide explains an equivalent sound level, or Leq, as an overall measure over a stated period; it is different from the maximum reached during an event.

JLARC describes some residents finding a constant drone or hum disruptive even when readings complied with local limits. Volume, frequency and duration describe different parts of that experience. A lower level can still be audible during the quiet intervals between louder events.

A-weighted measurements reduce the contribution of lower frequencies. C-weighted measurements retain more of that low-frequency sound. JLARC recommended that Virginia clarify local authority to use alternative metrics and enforcement approaches in its December 2024 report.

A local assessment can identify the applicable metric and limits, establish existing background sound, and compare predictions with operating measurements. Recording equipment load and conditions makes the comparison easier to interpret. The applicable ordinance supplies the legal test; the study supplies the acoustic information.

Match the approval path to local rules

JLARC describes several approval paths in Virginia. A by-right use follows requirements already established in the zoning ordinance. A special permit or rezoning involves a separate approval process that can provide opportunities for additional conditions under the local legal framework.

The distinction matters when readers ask what commissioners can do. Planning staff can identify the property's zoning, the required approval and which conditions or standards apply. A comprehensive plan describes the community's long-term development direction; the zoning ordinance supplies enforceable development rules.

Fairfax's 2024 amendment also preserves eligible prior approvals under transition provisions. For a particular project, the approval history helps establish which version of the rules governs its plans.

After construction, the responsible enforcement office and operator provide another part of the process. A clear route for reporting sound, arranging measurements and addressing a verified violation makes the approval conditions usable in practice.

Keep the siting debate and sound evidence distinct

People also debate why data centers face opposition. In his review of opinion polling, Cremieux interprets much of that opposition as NIMBYism rather than specifically fear of AI.

That is a debate about public attitudes. An acoustic study addresses the equipment, operating conditions and sound at particular locations. Calling an objection NIMBYism does not identify which fan is audible; calling a facility quiet does not supply its measurements.

Residents' accounts can identify places and times worth examining. Engineers can test the design and operation there. Residents' observations and engineers' measurements answer different questions; both can be part of the record.

Understanding a local proposal

Start with the full site and equipment plans, acoustic study and applicable zoning and noise rules. Planning staff can explain the approval path; an acoustic engineer can explain predictions and measurements. The operator and enforcement office can explain testing schedules, reporting and follow-up responsibilities.

Five questions help connect the plan to the neighbor experience:

• Where are the cooling equipment and generators relative to homes and other nearby uses, and what enclosures or barriers are proposed?
• Does the model cover the planned phase and full buildout, with the expected operating loads and relevant testing conditions?
• Which sound metrics, locations, time periods and limits apply, and how does the predicted sound compare with existing trains, traffic or industry at those same locations, including quieter nighttime periods?
• What field measurements will check the installed equipment, and where will the results be available?
• Who handles reports after opening, measures possible violations and ensures any required remedy is completed?

Location, equipment design and a sound model checked against field measurements are the main tools in this process. The public record shows how each was used for a particular facility.