Chirp Method Simulation (ISO 18233): How You Convert 'Exposure Time' into SNR and Replace 1,600 W with 0.3 W
Instead of shouting into the hall with thousands of watts, we simply measure a few seconds longer. Listen to octave chirp sequences (16K to 1024K) and watch cross-correlation suppress ambient noise by up to +54 dB – during normal office hours without hearing protection.
Lab Cockpit: Chirp Generator, Cross-Correlation & Processing Gain
Select a chirp sequence length, play the sweep via Web Audio, and watch the green Schroeder curve mathematically punch through the red noise floor.
Web Audio Synthesizer: Logarithmischer Sinus-Sweep in Echtzeit berechnet.
Physikalische Prinzipien & Praxis-Details nach Dr.-Ing. Frank Jordan
Exposure Time Instead of Floodlights: Acoustic Long Exposure
Every doubling of measurement duration (chirp length) theoretically yields a +6 dB gain in signal-to-noise ratio, allowing you to reduce speaker output by 6 dB (one quarter of amplifier power). That is why a 10 W chirp (or just 0.3 W over a 3-minute sweep) replaces a 1,600 W power amplifier required by interrupted pink noise. Consider the photography analogy: shooting a dark cathedral at night gives you two choices. Either illuminate the nave with 10,000 W floodlights (= 1,600 W pink noise at 110 dB) – or place the camera on a tripod and expose for 20 seconds. Because the building is time-invariant, the long-exposure shot is bright, razor-sharp, and grain-free.
Why the Chirp is Pink (-3 dB/Oct) and Ignores Loudspeaker Distortion
Although a logarithmic chirp sounds like a rising sine tone, its power spectrum rolls off at -3 dB per octave toward high frequencies—just like pink noise (protecting tweeters and focusing energy in the bass). Because the sweep progresses slowly at low frequencies and accelerates exponentially upward (spending equal time per octave), acoustic energy is concentrated where room modes and HVAC noise peak. Concurrently, every doubling of chirp duration (T) theoretically yields a +6 dB SNR gain in cross-correlation (or requires one quarter of amplifier power for identical SNR). The mathematical brilliance of deconvolution: harmonic distortion products (k2, k3) travel faster than the fundamental. When deconvolving, distortion spikes appear on the negative time axis BEFORE the true impulse response and are cleanly trimmed off. You can push a compact 2.5 kg speaker to its acoustic limits with zero effect on RT60 precision!
Ghost Chirping Above 10 kHz: What Are You Actually Hearing?
When adults listen to an audio sweep from 20 Hz to 20 kHz, natural age-related hearing loss would typically cause silence above 12–14 kHz. Yet listeners often hear a faint downward gliding 'tweet': this is not the acoustic sweep, but rather intermodulation / aliasing distortion created inside cheap laptop or smartphone speakers! In certified metrology chains with high-grade audio interfaces (96 kHz / 24-bit), this does not occur – and even if present, cross-correlation completely disregards it.
Excursion Protection: Why You Shouldn't Force 20 Hz into Small Cones
During long sweeps (20 to 180 seconds), the signal spends significant time in deep bass. Forcing a compact 2.5 kg active box with a 4-inch woofer to reproduce 20 Hz or 30 Hz at high volume can cause violent bottoming out against the pole piece. In Akulap, set the low cutoff to 80 Hz for room acoustic testing (DIN 18041). This fully covers the 125 Hz octave, protects the driver, and maximizes acoustic output safely.
The Chirp Method in Video Masterclasses & Podcast by Dr. Frank Jordan
Deepen your expertise with original lectures: Logarithmic sweep theory, step-by-step Akulap tutorial, and the in-depth audio podcast.
🎧 Podcast: The Chirp Method – Measuring RT60 with Compact Speakers
In-depth audio podcast by Dr. Frank Jordan covering exposure time, +54 dB SNR, office testing, and speaker driver protection.
The Magic of the Logarithmic Sine Sweep | Room Acoustics Masterclass
International masterclass explaining the mathematical foundations by Angelo Farina and ISO 18233.
Akulap Tutorial: Real-World Reverberation Time Testing with Chirps
Step-by-step field measurement with Akulap, USB measurement mic, and 2.5 kg active speaker.
Turnkey Package: Akulap Software, USB Mic & 2.5 kg Active Speaker
No more hauling heavy flight cases: The Akulap turnkey kit weighs less than 4 kg including microphone, speaker, and cables – ready to measure in 3 minutes.
Package for room acoustics
With this package you can measure various parameters for room acoustics
active loudspeaker for room acoustics
active loudspeaker for room acoustics
AkuLap module room acoustics ISO3382
AkuLap module room acoustics ISO3382
Ready for Certified Acoustic Metrology Without Back Pain?
Explore all hardware options in the Sound Sources Hub or calculate absorbers and target reverberation times in the Room Acoustics Hub.