Typical field SPL uncertainty?

Class 2: ±3-5 dB expanded (95%). Class 1: ±2-3 dB. Proper calibration, windscreens, averaging minimizes within these ranges.

Sound speed: 0.6 m/s per degree C. Mic sensitivity: 0.01 dB per degree C. Indoor climate-controlled: minimal. Outdoor: significant for delay calculations.

ISO 3382-1: at least 3 source x 3 receiver. SPL: 3+ one-minute samples. Each doubling reduces random uncertainty 3 dB.

What to include in reports?

Instrument details, calibration, method, positions, conditions, background noise, averages, standard applied, deviations. Enables verification and acceptance.

Typical field SPL uncertainty?

Class 2: ±3-5 dB expanded (95%). Class 1: ±2-3 dB. Proper calibration, windscreens, averaging minimizes within these ranges.

Sound speed: 0.6 m/s per degree C. Mic sensitivity: 0.01 dB per degree C. Indoor climate-controlled: minimal. Outdoor: significant for delay calculations.

ISO 3382-1: at least 3 source x 3 receiver. SPL: 3+ one-minute samples. Each doubling reduces random uncertainty 3 dB.

What to include in reports?

Instrument details, calibration, method, positions, conditions, background noise, averages, standard applied, deviations. Enables verification and acceptance.

Measurement Accuracy — Uncertainty & Repeatability

Measurement Accuracy & Uncertainty

Accuracy describes closeness to truth; repeatability describes consistency. Understanding uncertainty sources produces reliable measurements supporting engineering decisions and regulatory compliance per the GUM framework.

IEC 61672-1:2013§5ISO 3382-1:2009§6GUM:2008

Instrument

IEC 61672: ±1.1 dB Class 1, ±1.4 Class 2 at reference. Total: ±1.5/±2.5 dB root-sum-square across range.

Environmental

Temperature: ±0.6 m/s per degree C sound speed. Mic: ±0.01 dB/degree C. Wind: turbulent pressure. Humidity affects above 4 kHz.

Spatial

RT60 varies 5-15% across positions. ISO 3382-1 addresses via spatial averaging. Single-position overstates certainty.

Reducing

Calibrate, windscreen, record conditions, average multiple positions. Report method and conditions for transparency.

Budget

Per GUM. Expanded uncertainty (95%): ±2 dB lab, ±5 dB field.

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