Temperature Effects

Temperature affects several components of the measurement chain:

Microphone sensitivity: Condenser microphone sensitivity changes approximately ±0.01 dB per °C due to diaphragm tension and backplate capacitance changes
Preamplifier electronics: Gain drift of quality instruments is typically <0.01 dB/°C
Battery voltage: Cold temperatures reduce battery capacity and voltage, potentially affecting dynamic range
Speed of sound: Temperature changes the speed of sound (approximately +0.6 m/s per °C), affecting the relationship between frequency and wavelength

For ANSI S1.4 Type 1 instruments, the operating range of -10°C to +50°C must maintain all specifications. Type 2 instruments have a narrower range of 0°C to +40°C.

Humidity Effects

Relative humidity affects measurements in two ways:

Microphone: High humidity (>90% RH) risks condensation on the diaphragm, causing erratic readings. Very low humidity (<20% RH) can cause electrostatic charging.
Sound propagation: Atmospheric absorption is strongly humidity-dependent, particularly above 2 kHz. At 4 kHz, absorption varies from 0.01 dB/m at 80% RH to 0.04 dB/m at 20% RH (20°C). This affects measurements over long distances but is negligible for near-field work.

Atmospheric Pressure

Condenser microphone sensitivity depends on atmospheric pressure because the diaphragm tension resists the acoustic pressure signal. The effect is approximately:

ΔL ≈ 20 · log₁₀(P/P₀) dB

Where P₀ is the reference pressure (101.325 kPa at sea level). At 1500 m altitude (P ≈ 85 kPa), the shift is approximately -1.5 dB. This must be accounted for when comparing measurements at different altitudes or using a sea-level-calibrated instrument at elevation.

Wind

Wind-induced noise is the dominant environmental error source for outdoor measurements. See microphone windscreen requirements for protection strategies. Wind speeds above 5 m/s can invalidate measurements even with windscreens.

Electromagnetic Interference

Strong RF fields (near transmitters, radar installations) can couple into the measurement electronics. ANSI S1.4 requires instruments to be tested for immunity to standard electromagnetic environments. In practice, keep the sound level meter away from high-power radio transmitters and mobile phones during measurement.

Correction Practices

For precision work (Type 1, ISO 3382 reporting), document environmental conditions and apply corrections when measurements are taken outside the calibration conditions. For routine Type 2 field work, environmental effects are generally within the tolerance budget and do not require explicit correction.

SonaVyx Approach

The SonaVyx SPL meter processes the digital signal from the microphone, so the electronic processing chain is not subject to temperature drift. However, the phone microphone itself is affected by environmental conditions. For OSHA compliance measurements, document ambient conditions alongside your SPL readings.