Display Settings
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Phon Levels
About Equal Loudness Contours
What are these curves?
These are equal-loudness contours from the ISO 226:2003 standard. Each curve represents a constant perceived loudness (measured in phons) across different frequencies.
The key insight: we don't hear all frequencies equally well. A 100 Hz tone might need to be much louder than a 1 kHz tone to sound equally loud to our ears.
Interactive features
- Hover or tap: See the SPL (Sound Pressure Level) values at any frequency and phon level
- Toggle curves: Use the settings to show/hide specific phon levels
- Regions: Activate speech and music regions to see typical operating ranges
- Delta values: The tooltip shows Δ dB-how much more/less SPL is needed compared to 1 kHz
The 3-4 kHz dip
We're most sensitive to frequencies around 3-4 kHz. Notice how the curves dip there-less SPL is needed for the same loudness.
Low frequency sensitivity
Below 100 Hz, the curves steepen dramatically. Deep bass notes need significantly more SPL to be perceived as loud as mid-range tones.
Threshold of hearing (0 phon)
The dotted line at the bottom represents the quietest sounds humans can detect-the absolute threshold of hearing.