How loud is a mining site, and what to do about it

An air cooled miner is a rack of fans working continuously at close to full speed. At one metre a modern machine typically sits somewhere in the seventies to mid eighties on the decibel scale, roughly a vacuum cleaner held at arm's length, running every hour of every day. Ten of them are not ten times louder, but they are meaningfully louder, and a hundred is a different kind of problem entirely.

Why the decibel figure understates it

Two things make mining noise carry further than the number suggests. It is broadband, containing a wide spread of frequencies rather than a single tone, and it never stops. Human tolerance for constant sound is far lower than for intermittent sound at the same level, which is why a neighbour who cheerfully ignores a motorway will complain about a mining shed at a third of the volume.

Low frequency content is the part that travels. High frequencies are absorbed by air, foliage and walls within a short distance. The low end passes through most of that and is what people hear indoors at night with the windows shut. Any mitigation that only addresses the hiss and ignores the hum has solved the easy half.

The three cooling routes, ranked by noise

• Air. The loudest by a wide margin, and the only route where noise is usually the binding constraint on where you can build.
• Hydro. Dramatically quieter, typically around fifty decibels at the machine, because the heat leaves in water rather than in moving air. The noise moves outdoors to the dry cooler, which is a fan array you can site away from people.
• Immersion. Quietest at the tank, near silent in the room. The pumps and the external heat rejection still make sound, but again you choose where they sit.

This is one of the strongest practical arguments for hydro or immersion, and it rarely appears in a spec comparison. If the site is anywhere near a residence, the cooling decision in air, hydro or immersion is partly a planning decision.

Measure before you commit

Take a background reading at the nearest occupied building before signing anything, at night, in still conditions, over several hours. Night matters because ambient noise falls and the limits that apply are usually stricter. Still conditions matter because wind both masks noise and carries it, depending on direction, and the complaint will come on the night the wind blows towards the house.

Write the number down. If a dispute arrives later, the difference between your site's contribution and the background that was already there is the entire argument, and nobody can reconstruct the background after the machines are running.

What actually reduces noise

• Distance. The cheapest tool by far. Sound falls off with distance from the source, and doubling the separation buys more than most engineered solutions.
• Change the cooling route. Moving from air to hydro removes the problem at the source rather than treating it.
• Attenuators on intake and exhaust. Baffled ducts that let air through and absorb sound. Effective, and they cost static pressure, so the fans work harder. Budget the airflow penalty.
• Mass between source and neighbour. Solid walls and earth berms work on low frequencies. Fences and acoustic blankets mostly do not.
• Underclocking. Lower frequency means lower heat means slower fans. It costs hashrate and can be run seasonally or only at night, which is when it matters. See tuning a fleet.
• Fan replacement. Larger, slower fans move the same air at less noise. Check the warranty position before changing anything.

The mistake to avoid

Building first and treating noise as a problem to solve if someone complains. Retrofitting attenuation into a running site costs multiples of designing it in, and by then you are negotiating from a position where the other side can have you switched off. The planning authority does not care that the machines are already paid for.