"The pumps will be quiet." A line in every proposal we have ever inherited from a previous supplier. It is the line that produces the 02:00 phone call eight months after commissioning, when the guest in the nearest suite has finally complained to the GM after a week of trying to ignore it. By that point the pump is installed, the slab is poured, and the fix is six figures.
The line that protects the lodge is a number. Specifically, a measured A-weighted sound-pressure level at a defined distance, under defined operating conditions, recorded at commissioning and written into the handover pack.
What "55 dBA at 1m" actually means
Decibels are a logarithmic measure of sound pressure relative to the human hearing threshold. The A-weighting curve approximates the sensitivity of human hearing. Sixty dBA is normal conversation. Fifty dBA is a quiet office. Forty-five dBA is a library. Lodge guests in a suite near a plant room expect "outside-the-bush-camp quiet" — which the literature places at 35–45 dBA inside the suite (WHO, 2018).
By the time sound has travelled from the plant-room enclosure through the wall and across to a suite 6 m away, you typically lose 15–22 dBA depending on the wall construction and the geometry (Bies & Hansen, 2017). That means the plant-room outer-skin emission needs to sit below ~55 dBA at 1m to deliver guest-side comfort.
How to measure it — properly
A Type-1 sound-level meter, calibrated, A-weighted, slow time-constant, 1 m from the loudest face of the pressure set, under nominal load (60% pump speed, single duty running). Measurement repeated at the next nearest face. Highest reading is the recorded number. The meter, the operator, the date and the operating condition all appear on the handover sheet. The measurement is repeatable; the GM can produce it for an angry guest.
If the proposal in front of you does not name an acoustic number, it is not a serious proposal. The pump-room is going to sound like a pump-room — and the guest will let you know.
