Field Story

Open Office: Where Secrets Travel

An open-plan office handling sensitive financial data failed ASHRAE speech privacy requirements with D2,S measured at only 4 dB per doubling of distance, versus the 9 dB minimum. RTA measurements confirmed that the low-frequency sound masking system was miscalibrated, producing masking noise 8 dB below spec. Recalibrating the masking system and adding absorption to the ceiling plenum achieved D2,S of 10 dB.

Open Office

Spectrum Analyzer Measurement per ANSI S1.4

TL;DR

ANSI S1.4 performance specifications apply to the sound level meter that often serves as the front-end for spectrum analysis. The standard defines the accuracy requirements for the frequency weighting networks and the dynamic range of the measurement chain, both of which directly affect spectral measurement quality. When performing octave band analysis for noise assessment, ANSI S1.4 Class 1 or Class 2 tolerances determine the confidence interval of your per-band results. SonaVyx digital implementation achieves tight filter tolerances that meet or exceed ANSI S1.4 Class 2 specifications across the full analysis bandwidth.

ANSI S1.4 for Spectral Measurement

ANSI S1.4 and the companion ANSI S1.11 (for octave band filters) together define the performance envelope for spectrum analyzers used in professional noise assessment. Understanding these specifications ensures your measurements are valid for regulatory and engineering purposes.

Filter Specifications

  • ANSI S1.11 defines octave and 1/3-octave band filter characteristics
  • Class 0, 1, and 2 filters with progressively wider tolerances
  • Class 2 passband ripple: plus or minus 0.5 dB
  • Attenuation at band edges must meet minimum rejection specifications

Dynamic Range for Spectral Analysis

  1. Each octave band channel must have adequate dynamic range independently
  2. The noise floor per band may differ from the broadband noise floor
  3. Typical requirement: 70 dB dynamic range per band for Class 2
  4. Digital implementations can achieve 90+ dB per band with 24-bit audio

Calibration for Spectrum Analysis

Calibrate the system at 1 kHz using a pistonphone or acoustic calibrator, then verify that the calibration applies correctly across the full frequency range by checking against known spectral standards.

Common Mistakes

  • Assuming broadband calibration applies uniformly to all octave bands
  • Not verifying filter rolloff characteristics at band edges
  • Exceeding the linear operating range of the measurement chain at peak frequencies
  • Reporting band levels with more precision than the instrument class supports

SonaVyx Approach

The SonaVyx spectrum analyzer uses digital filters meeting ANSI S1.4 Class 2 specifications. Verify overall levels with the SPL meter. Apply calibration to improve accuracy. Use the problem detector for anomaly identification. Check room acoustics with the RT60 tool. See our learning modules for spectral analysis techniques.

Standard Reference

ANSI S1.4:

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Last updated: March 19, 2026