The fans and generators run day and night. How loud that is at the property line, and how far the hum carries.

We lay out where the noise comes from, what other towns have actually measured, and what is and isn't known for the two local sites. Where a figure comes from another city rather than from Prichard or Calvert, we say so.

The hum comes from the cooling, and it carries.

Most of the sound a data center makes comes from cooling. Fans and chillers run around the clock to keep the servers from overheating, and cooling is roughly 40 percent of all the electricity a data center uses. What people nearby tend to notice is not a loud roar but a constant low-frequency hum. That kind of sound travels a long way and, for some people, works its way through walls and windows at night. Reporting on data centers describes neighbors comparing it to a mosquito buzz or a drone that never stops.1,2

It is real, and it is hard to pin down with a meter.

The best-known case is Chandler, Arizona, where a data center gave off a hum that neighbors said rattled windows at night. The company traced it to its cooling fans and added muffling equipment, and the city went on to require new data centers to run a sound study before building, put mitigation in place, and take follow-up readings after opening. In Prince William County, Virginia, residents have measured data-center noise above 60 decibels at their homes. Part of what makes this so slippery is that much of the energy sits in the low-frequency range, which a standard decibel meter can understate, so a facility can look like it is within a limit on paper while still keeping people awake.3,4,5

Prichard and Calvert.

Prichard (Edged). The Prichard site would sit close to homes in and around Africatown, so the distance to the nearest neighbors is short. Edged's cooling runs on fan-driven dry coolers, and the backup diesel generators are test-run on a schedule (see Diesel & air), which lays a louder, periodic noise on top of the steady hum. No sound study, no fence-line noise limit, and no set hours for generator testing have been made public for the site yet.6

Calvert (Beacon). The Calvert campus would be far larger, which means more cooling and more fans, on rural land where the background is quiet and sound carries farther. Beacon says the site will have no diesel generators, so the periodic generator noise would not apply here, though the round-the-clock fan noise still would. On its Calvert page, the company promises a minimum 1,000-foot setback between critical equipment and the property lines, and says "worst-case calculations predict noise at the property lines well below the allowable limit of 65 decibels… comparable to the noise of a household refrigerator." A household refrigerator is about 40 decibels; 65 decibels is closer to normal conversation, so those two comparisons describe very different levels. And "the allowable limit" is unattributed: unincorporated Mobile County has no noise ordinance we have found. The "worst-case calculations" themselves have not been published. The concrete ask, exactly what Chandler now requires, is to release the sound study and commit to follow-up readings once the site is running.7,8