Interrupted Noise Method Simulation (ISO 3382): Why Ambient Noise Corrupts Your RT60 and Forces 1,600 Watts
The classical method of our grandfathers is wonderfully intuitive – as long as the hall is dead silent. Increase ambient noise in the simulator, listen to the interrupted decay, and watch the regression slope tip over while the 1-meter datasheet trap strikes.
Lab Cockpit: Noise Interruption, Decay Tail & Power Calculator
Trigger pink noise excitation, adjust microphone distance and ambient noise floor. Watch the ISO 3382 nonlinearity error index C escalate.
⚠️ The 1-meter datasheet trap: At 8 m distance, sound pressure is substantially lower than on the 1 m test bench!
Web Audio Synthesizer: 3s Rosa Rauschen -> Cutoff -> Raumhall + Störlärm.
📐 Transparency Check: How is this power calculated? ▼
Note: Datasheet specs apply to 1 m free-field at 1 kHz. In a room beyond the critical radius, equivalent absorption area A = 0.161·V/T60 governs SPL: Lp = LW + 10·lg(1/(4πr²) + 4/A).
The 1-Meter Datasheet Illusion & 100 dB Calculation
For a certified T30 measurement, ISO 3382 requires the excitation level to exceed ambient background noise by at least 45 dB (ideally 50 dB). If HVAC generates 50 dB SPL at 125 Hz in an office or classroom, the microphone requires at least 100 dB continuous SPL! The datasheet trap: manufacturers specify sound power at 1 m free field. At 6–10 m distance in real rooms, levels drop significantly due to distance and boundary absorption. To force 100 dB at the mic, amplifier power must be multiplied tenfold!
ISO 3382 Nonlinearity Index C: When the Meter Lies
When ambient noise intrudes into the T20 or T30 regression interval, the decay curve prematurely flattens into a horizontal noise floor. Handheld meters that blindly apply linear regression will fit across this bend. The result: the slope tilts far too flat, reporting 2.8 s instead of the true 1.2 s! The ISO 3382 nonlinearity parameter C measures deviation from a true straight decay. Values of C > 5 % indicate serious ambient corruption.
Field Guide: Measuring RT60 with Pink Noise & NTi XL2 (incl. Noise Floor Cliffhanger)
Watch NTi Audio's official tutorial on RT60 measurement with interrupted pink noise. Pay close attention to timestamp 2:12 min explaining background noise limitations.
Mandated by Tender or Building Code to Measure with Interrupted Noise?
When tender specifications or building acoustics standards (ISO 16283) require a 360° omnidirectional source, we offer certified dodecahedrons and power amplifiers for purchase, demo discounts, or rental.
Ntek OMNI 4 LT omnidirectional soundsource
lightweight omnidirectional soundsource with 12 loudspeakers
Ntek OMNI 4 HP omnidirectional soundsource Demo unit
12 loudspeakers as an omnidirectional soundsource
No desire to haul 1,600 W amplifiers and 15 kg of gear?
See on Page 3 how the Chirp Simulator solves this identical 50 dB HVAC measurement with a 2.5 kg active speaker and just 0.3 W of power – during regular office hours!