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

RTA Measurement per ANSI S1.4

TL;DR

ANSI S1.4 specifies the accuracy requirements for sound level meters that serve as the measurement front-end for real-time analyzers. The standard defines frequency weighting, detector response, and dynamic range specifications that determine the quality of per-band RTA measurements. Understanding these specifications helps you evaluate the confidence interval of your RTA readings and determine whether they are suitable for regulatory reporting. SonaVyx digital RTA implementation meets ANSI S1.4 Class 2 specifications for the processing chain while leveraging modern audio hardware for maximum dynamic range.

ANSI S1.4 and RTA

The RTA is essentially a multi-channel sound level meter displaying simultaneous octave band levels. ANSI S1.4 performance specifications apply to each band independently.

Per-Band Accuracy

  • Each octave band has its own accuracy tolerance per ANSI S1.4
  • Class 2: plus or minus 1.4 dB at mid-frequencies, wider at extremes
  • The displayed bar graph uncertainty varies across the frequency range
  • Mid-frequency bands (250 Hz to 4 kHz) have the best accuracy

Dynamic Range per Band

  1. Each band must have independent dynamic range adequate for the application
  2. ANSI S1.4 Class 2 requires 60 dB minimum dynamic range
  3. Digital implementations typically achieve 80-90 dB per band
  4. The limiting factor is usually the microphone noise floor

Calibration

Calibrate at 1 kHz and verify that the calibration propagates correctly to all bands. For critical measurements, verify selected bands against known spectral references.

Common Mistakes

  • Treating all octave bands as equally accurate
  • Not specifying the instrument class when reporting RTA measurements
  • Exceeding the dynamic range in loud environments

SonaVyx Approach

The SonaVyx RTA meets ANSI S1.4 Class 2 digital processing specifications. Verify calibration with the SPL meter. Check room conditions with the RT60 tool. Use the problem detector for automated analysis. Run AI diagnostics for recommendations. See our learning modules for RTA techniques.

Standard Reference

ANSI S1.4:

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Last updated: March 19, 2026