Hum, tones & distance

Could residents hear it?

Short answer

Yes, depending on equipment, distance, terrain, weather, and mitigation. The most defensible concern is persistent audible or near-audible low-frequency hum, not a claim that inaudible infrasound has been proven to cause a broad list of diseases.

Why one dBA number is not enough

A-weighting intentionally discounts low frequencies. It subtracts roughly 50.5 dB at 20 Hz, 26.2 dB at 63 Hz, and 16.1 dB at 125 Hz before combining the result into one dBA value.

That means a meter can correctly display a modest dBA result while a low-frequency tone remains noticeable. A useful investigation records:

A-, C-, and Z-weighted levels
One-third-octave bands, especially 8–200 Hz
Narrowband spectra for tones and modulation
Nighttime, full-load, and generator-test conditions
Weather and equipment operating logs
Both outdoor receiving properties and affected indoor rooms

What the evidence supports

Supported

Persistent industrial hum can cause annoyance and disturb sleep or concentration.
Residents have complained at data-center sites that complied with ordinary dBA limits.
Low-frequency sound travels and penetrates building envelopes differently from speech-frequency sound.
Occupational hearing-loss limits are not suitable community quality-of-life standards.

Not established

That every data center emits problematic infrasound
That inaudible environmental infrasound from data centers has been proven to cause vertigo, cardiovascular disease, or other chronic illness
That a frequency by itself determines a universal safe setback

Controlled studies generally have not detected acute physiological or sleep effects from infrasound at or below perception thresholds. Long-term residential evidence remains limited.

Distance is not a guarantee

For a compact source in open space, sound starts with a rule of thumb of about 6 dB reduction per doubling of distance. Real campuses are more complicated: rows of fans behave differently from a point source, multiple units combine, buildings reflect sound, and wind or nighttime inversions can improve propagation.

Low frequencies have long wavelengths, about 56 feet at 20 Hz and 18 feet at 63 Hz, so ordinary walls and small barriers are less effective than they are against higher-frequency sound.

Practical ordinance protections

No exemption for cooling or HVAC equipment
Cumulative limits covering every phase and generator
Stricter nighttime and tonal protections
Frequency-band limits in addition to dBA
Baseline measurements before construction
Independent modeling under propagation-favorable weather
Post-construction testing at peak cooling load
A rapid complaint and retesting process
Enforceable mitigation, including equipment changes or reduced nighttime operation

Safe public statement

Data-center low-frequency noise is a legitimate siting and quality-of-life issue. The evidence supports frequency-aware measurement and enforceable prevention. It does not support presenting every reported symptom as medically proven infrasound injury.