Calibrated frequency-domain approximation of the ARL Auditory Hazard Assessment Algorithm for Humans. Transfer functions and thresholds match published ARL specifications. Adjust parameters to explore how each variable drives ARU.
ARU contribution at each of the 23 basilar membrane locations. The peak location determines total single-impulse ARU. The risk multiplier (rightmost column) shows how much the ear's combined transfer function amplifies each frequency relative to the input — this is the effective weighting coefficient.
Why does ~3-4 kHz dominate? Three factors compound: (1) the ear canal resonance adds ~12 dB gain around 2.7 kHz, (2) the middle ear transfer function peaks near 1-2 kHz, and (3) the cochlea has intrinsic anatomical vulnerability at 3-6 kHz — which is why noise-induced hearing loss classically shows a "4 kHz notch" on audiograms regardless of the noise spectrum.
How the impulse spectrum transforms through each stage of the ear. The gap between the free-field and cochlea curves shows where your protection and ear transfer function are working hardest.
How much a ±1 unit change in each parameter affects total ARU from current settings.
| Parameter | −1 | Current | +1 | Impact |
|---|
ARU across the full peak SPL range with current settings.
The AHAAH model is an electro-acoustic circuit model of the full human ear developed by the U.S. Army Research Laboratory.
Ear canal resonance adds ~12 dB gain at 2.5-3 kHz. This amplification is a major reason the 3-4 kHz region dominates damage.
Ossicular chain peaks near 1-1.2 kHz (+6 dB/oct below, −8 dB/oct above). Nonlinear annular ligament clips stapes at ~20 μm. Stapedius reflex provides ~20 dB attenuation below 1 kHz when "warned."
Stapes drives a traveling wave along the basilar membrane. WKBJ approximation computes displacement at 23 points (~⅓ octave). Base = high freq, apex = low freq.
At each BM location, upward flexes are tracked — amplitude in microns is squared and summed: ARU = Σ(d²). Maximum across 23 locations is reported. CTS = 26.6×ln(ARU) − 140.1.
The cochlea has intrinsic vulnerability at 3-6 kHz due to anatomy (blood supply, mechanical tuning). Combined with ear canal resonance, this makes the 3-4 kHz band the dominant damage driver.
Short A-durations produce broad spectra (more high-freq energy → more damage). Longer pulses concentrate energy at lower, less damaging frequencies. Suppressors lengthen the pulse and shift energy down.