Place Theory

A travelling wave peaks at one spot on the 35 mm basilar membrane; that spot's location IS the pitch, and loud sound that kills it wipes out that pitch forever.

What it is

Pitch is decided by WHICH physical spot on your inner ear's basilar membrane vibrates the most.

Key facts

• Human hearing range: 20 Hz to 20,000 Hz (20 kHz) for a healthy young ear.
• The basilar membrane is ~35 mm long, coiled in the cochlea (snail-shaped inner ear); pitch maps to PLACE = 'tonotopic'.
• BASE (near oval window) is STIFF + narrow = HIGH freq (~20 kHz); APEX (far tip) is FLOPPY + wide = LOW freq (~20 Hz).
• Proposed by Hermann von Helmholtz (1863); refined by Georg von Bekesy's travelling-wave work (1961 Nobel Prize).
• Place coding dominates ABOVE ~5 kHz; below ~500 Hz the brain also uses nerve-firing TIMING (temporal/volley theory).
• ~3,500 inner hair cells per ear do the actual hearing; you're born with all of them and they DO NOT grow back.
• Aussie noise limit: 85 dB(A) over 8 h (Safe Work Australia); peak hard limit 140 dB(C) can cause instant damage.
• 3 dB exchange rate: every +3 dB HALVES safe time. 85 dB=8 h, 88 dB=4 h, 91 dB=2 h, 100 dB=15 min.
• Noise-induced loss shows a 'notch' at 3,000-6,000 Hz (centred ~4 kHz) on an audiogram before you even notice it.
• Inverse-square law: doubling distance from a point source = -6 dB SPL; doubling acoustic POWER = +3 dB. Sound speed = 343 m/s at 20 C.

How it works

1. Sound enters the ear canal and vibrates the eardrum.
2. Three tiny bones (ossicles) push the oval window, sending a pressure wave into the fluid-filled cochlea.
3. A 'travelling wave' runs along the basilar membrane and peaks at ONE specific spot.
4. High pitch peaks near the stiff base; low pitch peaks near the floppy apex.
5. Hair cells at that peak spot fire nerve signals down the auditory nerve.
6. The brain reads WHICH spot fired = the pitch you hear.

Real examples

• A 20 kHz tone shakes the base; an 80 Hz kick-drum sub shakes the apex, metres apart in 'pitch' but millimetres apart in the ear.
• Years of loud cymbals (~4 kHz energy) kill base hair cells, so a sound engineer can't hear 'air'/sparkle and over-boosts highs.
• Tinnitus often rings at the exact pitch of the damaged spot, commonly around 4 kHz.
• Telephone audio is band-limited 300-3,400 Hz, only exciting a middle strip of the membrane, which is why voices sound thin.

How it helps in live sound

• Wear earplugs at every loud gig: musician/'flat' plugs (e.g. Etymotic ER-20, -20 dB) cut level evenly without dulling tone.
• Treat 4 kHz as sacred: chronic damage notches there, so do not park a graphic EQ boosted hard at 4 kHz all night.
• Use an SPL meter on dB(A), 8 h slow; keep FOH/crew under 85 dB(A) average, hard-stop at 100 dB = 15 min exposure.
• High-mids fatigue ears first: if 2-5 kHz starts sounding harsh mid-show, it's your ears tiring, not the mix, so reference next day.
• Position monitor wedges and side-fills off your direct ear axis; cumulative HIGH-frequency dosage is what notches hearing.
• Take a quiet 5-10 min break each hour: hair cells recover from temporary threshold shift, but only if you give them silence.