Ensure the room is quiet and representative of its normal state. We will measure the ambient noise floor to establish a baseline. Close doors and windows, turn off unnecessary equipment, and position your device at ear height in the listening position.
Room acoustics measurement is the foundation of any serious audio environment — whether you are building a recording studio, optimizing a home theater, improving a classroom for speech intelligibility, or tuning a concert hall. Without objective measurement data, acoustic treatment decisions are guesswork. This guide covers the theory, standards, and practical methodology behind professional room analysis.
Reverberation time, formally defined in ISO 3382-1:2009, is the duration required for the sound pressure level in an enclosed space to decrease by 60 decibels after the sound source stops. It is the single most important metric in room acoustics because it directly affects speech intelligibility, music clarity, and listener comfort. The Sabine equation (T60 = 0.161V/A, where V is room volume in cubic meters and A is total absorption in sabins) provides a first-order estimate, but real rooms require measurement because absorption is rarely uniform across surfaces.
Modern measurement practice uses the Schroeder backward integration method rather than direct observation of the decay curve. By integrating the squared impulse response from the end backward, you obtain a smooth Energy Decay Curve (EDC) free of the random fluctuations inherent in individual decays. T20 and T30 are derived by fitting a linear regression to the first 20 dB or 30 dB of the EDC respectively, then extrapolating to 60 dB. ISO 3382-1 requires a minimum Impulse-to-Noise Ratio (INR) of 35 dB for T20 and 45 dB for T30 to ensure measurement validity.
Every enclosed space has resonant frequencies determined by its dimensions. In a rectangular room, axial modes occur at f = c/(2L) and its harmonics, where c is the speed of sound and L is the room dimension. A room that is 4 meters long has its first axial mode at approximately 43 Hz. Tangential and oblique modes add further resonances. Below the Schroeder frequency (approximately 2000 times the square root of RT60 divided by volume), individual modes are distinguishable and create peaks and nulls at specific positions in the room.
Room modes are the most challenging acoustic problem in small to medium rooms. They cause dramatic level variations — a 20 dB peak at one position and a 20 dB null just a meter away is not uncommon at low frequencies. Equalization cannot fix this because the mode pattern is position-dependent: correcting a peak at the mix position creates a larger peak elsewhere. Physical treatment with bass traps (porous absorbers at least 4 inches thick in corners, membrane absorbers, or Helmholtz resonators) is the only effective solution.
The room impulse response (RIR) contains all time-domain information about how sound propagates from source to receiver. The direct sound arrives first, followed by early reflections (within the first 50-80 ms) from walls, floor, and ceiling, then the late reverberant field. Early reflections are perceptually critical: they affect timbre (comb filtering), spaciousness (lateral reflections), and clarity (C50/C80 metrics). The ratio of early-to-late energy determines whether a room supports speech (high C50) or enveloping music (lower C80 acceptable).
The logarithmic sine sweep method, developed by Angelo Farina and standardized in ISO 18233, is the gold standard for RIR measurement. A sweep from 20 Hz to 20 kHz is played through the sound system and recorded at the measurement position. Deconvolution with the inverse sweep filter yields the impulse response with excellent signal-to-noise ratio and harmonic distortion rejection. SonaVyx implements this method in Rust WASM for real-time processing entirely in the browser.
Flutter echo occurs between parallel reflective surfaces and manifests as a rapid repetitive “buzzing” or “zinging” when you clap your hands. Treatment involves adding absorption or diffusion to at least one of the parallel surfaces. Excessive reverberation causes speech to become unintelligible and music to sound muddy. It is the most common problem in untreated rooms with hard surfaces. Comb filtering results from a reflected copy of the signal arriving with a short delay (1-20 ms), creating periodic nulls in the frequency response spaced at 1/delay intervals. Speaker placement and listener position optimization can minimize this.
First reflection problems occur when strong early reflections from nearby walls color the direct sound. Absorption panels at the mirror points (the location on the wall where a mirror would show the speaker from the listening position) are the standard treatment. SBIR (Speaker Boundary Interference Response) creates a broad null when the speaker is positioned near a wall and the reflected sound cancels the direct sound at the frequency where the path difference equals half a wavelength.
Effective room treatment uses three types of devices: absorbers reduce sound energy (porous materials like fiberglass, mineral wool, or acoustic foam), diffusers scatter sound evenly (QRD, skyline, or primitive root designs), and bass traps target low-frequency absorption (thick porous panels in corners, membrane absorbers, or tuned Helmholtz resonators). A balanced approach combines all three: absorption controls reverberation and first reflections, diffusion maintains liveness and spaciousness, and bass traps address modal problems.
Treatment priority typically follows this order: (1) bass traps in corners to control low-frequency modes, (2) absorption at first reflection points for imaging and clarity, (3) rear wall treatment (absorption or diffusion depending on room size), and (4) ceiling cloud for overhead reflections. The NRC (Noise Reduction Coefficient) rating indicates a material's average absorption across 250 Hz to 2 kHz. Materials with NRC above 0.85 are considered high-performance absorbers. SonaVyx's Treatment Calculator recommends specific products and quantities based on your measured RT60 and target values across all octave bands.
For reliable results, follow ISO 3382-1 guidelines: use at least 2 source positions and 3 receiver positions for spatial averaging. Ensure the ambient noise floor is at least 45 dB below the signal level (INR requirement). Measure in octave or 1/3-octave bands for RT60. Use the same temperature and humidity conditions for before/after comparisons, as the speed of sound varies with air temperature (approximately 0.6 m/s per degree Celsius). Document all equipment positions and room conditions for reproducibility.
SonaVyx automates much of this process: the Room Analysis workflow guides you through each step, validates measurement quality with INR checks, compares results against standards, and generates professional reports. All DSP processing runs locally in your browser via WebAssembly — no audio data leaves your device.