Professional browser-based SPL measurement with A/C/Z weighting
Noise Criteria (ASHRAE)
IEC 61672-1:2013 is the international standard for sound level meters, defining the performance requirements that ensure accurate and repeatable noise measurements worldwide. The standard specifies two classes of instrument: Class 1 (precision) and Class 2 (general purpose). SonaVyx implements Class 2 tolerances, which are achievable with calibrated smartphone and computer microphones.
Human hearing is not equally sensitive to all frequencies. A-weighting applies a filter that approximates the frequency response of the human ear at moderate listening levels, heavily attenuating low frequencies below 500 Hz and slightly boosting 2-4 kHz where our hearing is most sensitive. A-weighted measurements (dBA) are the most commonly required by noise regulations worldwide, including OSHA workplace exposure limits (85 dBA TWA) and WHO environmental noise guidelines.
C-weighting provides a nearly flat response across the audible spectrum, with rolloff only at the extremes below 31.5 Hz and above 8 kHz. Use C-weighting when measuring peak sound pressure levels or when evaluating systems with significant low-frequency content such as concerts, construction, or mechanical noise.
Z-weighting (zero weighting) is a perfectly flat frequency response with no filtering, useful for raw acoustic measurements and transfer function analysis.
The time constant determines how quickly the meter responds to changes in sound level. Fast (125 ms) is suitable for most environmental measurements and captures transient events. Slow (1000 ms) averages over a longer period, providing more stable readings for fluctuating noise sources. Impulse mode (35 ms attack, 1500 ms decay) captures short-duration events like hammering or gunshots while maintaining the peak reading.
Statistical noise levels describe the distribution of sound levels over a measurement period. L10 is the level exceeded 10% of the time, representing the loudest events. L50 (median) represents the typical noise level. L90 is exceeded 90% of the time, representing the background noise floor. The difference L10-L90 indicates the dynamic range or variability of the noise environment.
Without calibration, SonaVyx displays relative levels referenced to digital full scale. To obtain absolute dB SPL readings, use a 94 dB calibrator (pistonphone) at 1 kHz. Place the calibrator over the microphone and click the Calibrate button. SonaVyx also supports loading .cal files from measurement microphones like the Dayton Audio iMM-6 or miniDSP UMIK-1 for per-frequency correction.
With proper calibration using a 94 dB reference source, browser-based SPL meters can achieve IEC 61672-1 Class 2 accuracy (typically ±1.4 dB at 1 kHz). The main limitation is the microphone, not the software. External measurement microphones like the UMIK-1 significantly improve accuracy compared to built-in laptop or phone microphones.
Leq (equivalent continuous level) is the average sound energy over the entire measurement period, expressed as the constant level that would contain the same total energy. Instantaneous SPL is the time-weighted level at any given moment. Leq is preferred for regulatory compliance because it accounts for the cumulative noise exposure.
NC curves are a family of octave-band spectra used to evaluate background noise in occupied spaces. An NC rating is determined by the tangency method: the highest NC curve that any octave band touches. Typical targets: NC-25 for recording studios, NC-30 for offices, NC-35 for classrooms, NC-40 for open-plan offices.
SonaVyx provides IEC 61672-1 Class 2 compliant measurements when calibrated, which meets the ANSI S1.4-2014 Type 2 requirement. However, official OSHA compliance measurements typically require NIST-traceable calibration documentation. SonaVyx is ideal for preliminary surveys, screening, and ongoing monitoring.
Browser audio processing algorithms (echo cancellation, noise suppression, automatic gain control) are designed for voice communication and will corrupt acoustic measurements. SonaVyx automatically requests raw microphone access with these features disabled to ensure measurement integrity.