Cone of Confusion

A set of positions around your head where the left right ear cues are identical, so your brain cannot tell them apart on those cues alone.

Every dot on the ring feeds both ears identical timing and loudness — only head movement or pinna colouring breaks the tie.

What it is

A ring of positions around your head where both ears receive identical timing and loudness cues, so direction is genuinely ambiguous.

Key facts

Speed of sound in air = 343 m/s at 20 degrees C (rises ~0.6 m/s per +1 degree C)
Max interaural time difference (ITD) = about 660 microseconds (0.66 ms); zero on the median plane
ITD is the main cue below ~1.5 kHz; ILD (level) takes over above ~1.5 kHz where wavelength is shorter than head width (~21.5 cm)
Head shadow gives up to ~20 dB high-frequency attenuation to the far ear
Cone of confusion = surface of a cone about the interaural axis; every point shares the same ITD and ILD
Classic confusions: front/back mirror (e.g. 30 deg front vs 150 deg rear) and up/down mirror
Pinna (HRTF) notches typically appear ~6-10 kHz and shift with elevation to resolve the cone
Doubling distance from a point source = -6 dB (inverse-square law: -20*log10(2))
Halving power = -3 dB; doubling power = +3 dB; +6 dB = doubling sound pressure
Minimum audible angle ~1 degree dead ahead; localization blur worst directly behind and overhead

How it works

Sound arrives at both ears; brain compares arrival time (ITD) and loudness (ILD).
Any source on the same cone gives matching ITD and ILD, so those two cues alone can't separate them.
Front vs back and up vs down on that cone become indistinguishable.
Pinna shape filters incoming sound differently by angle, adding spectral notches.
Brain reads those notches (the HRTF) to break the tie and place front/back/height.
Tilting or rotating the head changes ITD/ILD dynamically and instantly resolves it.

Real examples

A mono vocal panned dead-centre can feel like it's coming from in front or from behind on small speakers.
Reversed surround speakers: audience hears a rear effect as if it's in front because cues match.
In-ear mixes feel 'inside your head' as pinna cues are bypassed, so the cone never resolves.
A bird overhead vs directly behind sounds identical until you tilt your head.
Eyes closed pointing at a click: most nail left/right but flip front/back.

How it helps in live sound

Don't rely on a static centre-panned mono source for space; add stereo width or early reflections.
Check surround/effects speaker polarity and channel mapping so rear FX don't read as front.
Add a touch of reverb pre-delay or HF EQ to give the brain spectral cues the cone lacks.
For immersive rigs, verify object front/back placement by walking the room, not just metering.
Decorrelate dual-mono sources (tiny delay or pitch shift) so they don't collapse onto one cone.
Place spot mics slightly off-axis so HF/pinna content survives and aids localization.

Everyday analogy

Like two stopwatches that read the same time whether the runner came from the front gate or the back gate, you can't tell the route until you turn your head and watch the clocks change.

Watch out

Myth: two ears are enough to locate any sound. Reality: on the cone of confusion both ears get identical ITD/ILD, so pinna spectral cues or a head movement are what actually resolve front/back and height.