ISO 3382-1 Excitation Sources: Loudspeaker, Swept Sine, and Impulsive Sources
TL;DR
ISO 3382-1 Clause 7 specifies excitation source requirements. An omnidirectional loudspeaker must have maximum directional deviation ≤1 dB in any 1/3 octave band up to 1 kHz, ≤3 dB up to 4 kHz, and ≤5 dB above 4 kHz. Swept sine (logarithmic chirp) is the preferred excitation signal for its superior SNR. MLS (Maximum Length Sequence) is an alternative with lower peak factor. Impulsive sources (starter pistols, balloons) are permitted but yield lower INR and non-uniform spectra. The source must produce sufficient level to achieve the required impulse-to-noise ratio.
Omnidirectional Loudspeaker (Clause 7.1)
The primary excitation source for ISO 3382-1 measurements is an omnidirectional loudspeaker placed at positions representative of actual sound sources (e.g., stage positions in a concert hall). The directivity requirements are:
| Frequency range | Max directional deviation |
|---|---|
| 125 Hz – 1 kHz | ±1 dB |
| 1 kHz – 4 kHz | ±3 dB |
| Above 4 kHz | ±5 dB |
Dodecahedral loudspeakers (12-driver polyhedron) are the standard choice for achieving these directivity requirements. The loudspeaker must produce sufficient power to achieve an adequate impulse-to-noise ratio in the room under measurement.
Swept Sine Excitation
Logarithmic swept sine (also called exponential chirp) is the recommended excitation signal for modern measurements. As detailed in AES-2id, the sweep provides excellent signal-to-noise ratio because all the acoustic energy is concentrated at one frequency at any instant. Deconvolution by the inverse sweep filter yields the impulse response with harmonic distortion products separated in time.
SonaVyx uses the Farina method for sweep generation with configurable duration (2-20 seconds) and frequency range (20 Hz – 20 kHz). Longer sweeps provide higher SNR.
MLS Excitation
Maximum Length Sequences are pseudo-random binary signals with flat power spectra. The impulse response is extracted via circular cross-correlation. MLS offers constant sound pressure level (no dynamic range issues) but is more sensitive to time variance — air conditioning fluctuations or audience movement during measurement can corrupt the result. See AES-2id signal processing for deconvolution details.
Impulsive Sources (Clause 7.2)
Starter pistols, balloon pops, and wooden clappers produce an impulse response directly. Advantages: simple, no equipment beyond the source. Disadvantages: non-repeatable level, poor low-frequency energy, limited SNR (typically only achieving T20-quality INR), and uneven spectral distribution. ISO 3382-1 permits impulsive sources but recommends loudspeaker-based methods for precision.
Source Level Requirements
The excitation source must produce sufficient level that the measured impulse response has an INR of at least 35 dB for T20 or 45 dB for T30 extraction per Clause 8.3. In large rooms (>10,000 m³), this may require a high-power amplifier and professional loudspeaker.
SonaVyx Source Options
For impulse response measurement, SonaVyx supports both swept sine and MLS excitation. In single-device loopback mode, the phone speaker serves as the source. For better results, use a separate speaker device via the multi-device measurement setup. The RT60 tool reports INR quality for each measurement.
Try It Now
Open this measurement tool in your browser — free, no download required.
Last updated: March 19, 2026