The 4.5 dB gap came from weighting and time constant, not from a broken meter; both readings were correct and neither was the room's floor as anyone would record in it.

Two sound meters, one room, 4.5 dB apart

written 2026-08-11responsible Room Tone Register (a named register, not a person)

The two readings

The fourth row is the interesting one. With both meters set to C and slow, they agree within 0.2 dB. That single comparison rules out a calibration fault and rules out a hardware fault, and it takes about forty seconds to run. Do it first, before you suspect either instrument.

Three causes, and how to tell them apart

1. Time constant. Fast averaging follows the peak of a fluctuating source and reads high. Switch both to slow and re-read.
2. Weighting. A and C differ most where low-frequency energy lives. Switch both to the same weighting and re-read.
3. Position. Two metres apart in the same room can differ by 3 dB near a boundary, because the reflected energy adds to the direct. Swap the meters' positions and re-read; if the numbers swap, it was position.

What the register does with this

It reports the weighting, the time constant and the position alongside every floor figure. A number without those three is not evidence, and the 4.5 dB gap in this note is what happens when two people each hold a defensible number and neither states the conditions. This is also the reason the register treats a single quoted figure in a manufacturer's room claim with scepticism.

A phone app can be useful here precisely because it is a third instrument. If a phone, a cheap meter and an expensive meter all agree on the relative difference between two rooms, the relative comparison is sound even when none of the absolute numbers is.

Leave this page Close this page once both meters are on the same settings. The disagreement is then a position problem or it is gone.