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This demo plays pure tones — alternating between your selected frequency and a 1 kHz reference. Headphones recommended. Start with master volume LOW; the lesson reveals itself when you turn it up.
Foundation · Module 2.2 · How You Hear
Equal Loudness
How loudness perception changes with frequency — and with overall volume.
Fletcher-Munson Equal-Loudness Contours (ISO 226:2003)
The Demo
Hear the contour for yourself
- Pick a low frequency — try 80 Hz. The widget alternates between your tone and a 1 kHz reference at the same digital level.
- Turn your master volume DOWN (around 20–30%). Press Play. The bass tone will sound much quieter than 1 kHz — even though they're at the same digital level.
- Now turn your master volume UP (around 70%). Press Play again. The two tones will feel much closer in loudness.
- That's it. That's Fletcher-Munson. Your ear isn't equally sensitive across frequencies, and the imbalance gets bigger at low listening levels.
What you're hearing
The widget alternates between your selected frequency and 1 kHz — both at the same digital level (−20 dBFS). You're hearing the same numerical loudness, but your ear perceives them differently. The further your test frequency is from 1 kHz (especially in the bass), the more obvious the perception gap.
Contour data from ISO 226:2003 standard, "Acoustics — Normal equal-loudness-level contours." Curves show the SPL (in dB) required at each frequency to produce a given loudness sensation, normalized to 1 kHz at the labeled phon level. Approximated for educational visualization.