How to use it
Put on headphones in a quiet room and turn the volume of your device down. In step 2, play the 1 kHz reference tone and raise the device volume until the tone sounds like a normal speaking voice. After that, leave the volume alone: every result is measured relative to that tone.
During a run two tones take turns: the 1 kHz reference, then a test tone of a different pitch; labels show which one is playing. Make the test tone louder or softer until both seem equally loud, then confirm. Judge only loudness, not pitch. Each match becomes a point on the graph. Run the soft and the medium level to get two curves.
Controls
- Louder / Softer: the buttons or the Up and Down arrow keys. Steps are 5 dB at first, 2 dB after your first change of direction and 1 dB after the second.
- Equally loud: the button or Enter stores the match and starts the next tone, in random order.
- Limit reached: appears at the highest level the page will play; press it (or L) to record that instead of a number.
- Pause (or Esc) stops all sound. Redo this tone restarts the current tone, Skip leaves it out, Stop ends the run and keeps the matches.
- Redo one tone: after a run, repeat any single frequency.
- Saved runs: the last twelve runs stay in this browser; Compare draws one as a dashed line. Export the chart as PNG, the numbers as CSV, or print.
How it works
Two tones with the same sound pressure level can differ a lot in loudness when their frequencies differ. Acoustics therefore uses the loudness level, measured in phons: a sound has 40 phons when it seems as loud as a 1 kHz tone at 40 dB SPL. An equal-loudness contour joins all combinations of frequency and level that sound equally loud.
Fletcher and Munson published the first widely used contours in 1933, measured with headphones. The curves were measured again with loudspeakers in 1956, and a large international study led to the revised standard ISO 226 in 2003. Its 2023 edition changed the values by 0.6 dB at most. The page computes the 2003 curves from the formula in the standard:
Af = 0.00447 · (100.025 LN − 1.15) + (0.4 · 10(Tf + LU)/10 − 9)αf
LN is the loudness level in phons, Lp the sound pressure level that produces it. The threshold Tf and the constants αf and LU are tabulated for 29 frequencies from 20 Hz to 12.5 kHz. The graph shows the 40- and 60-phon contours shifted to 0 dB at 1 kHz.
The curves dip between about 2 and 5 kHz, where the ear is most sensitive. A main reason is the ear canal: a tube about 2.5 cm long, closed by the eardrum, that resonates at roughly 3 kHz. On the 40-phon contour a 63 Hz tone needs about 33 dB more level than a 1 kHz tone; on the 80-phon contour only about 18 dB. The contours flatten as the level rises. That is why music played quietly loses its bass, why some amplifiers have a “loudness” button that boosts the bass at low volume, and why a mix balanced at low volume can sound boomy when played loud.
Your own curve also contains the frequency response of your headphones, which can differ by many decibels between models. The standard describes young adults listening with both ears to a source straight ahead in an echo-free space, not to headphones. And without calibration nobody knows how many phons your reference tone has; the 40- and 60-phon curves are only the nearest guesses. So compare shapes, not absolute values.
The procedure is the method of adjustment. Each test tone starts at a random level, alternately above and below the expected match, and the level stays hidden while you adjust.
Things to try
- Run both levels. The medium curve should rise less in the bass than the soft one.
- Use the full run and look at the 1 kHz self-check: matching two identical tones shows your own matching error.
- Repeat a run and compare it with the saved one. Differences of a few decibels are normal in loudness matching.
- Try another pair of headphones and set the volume again. The change in shape comes from the headphones, not from your ears.
- Redo a bass tone with the earphones sitting loosely. A leak lets the bass escape, so the match moves up.
Frequently asked questions
Is this a hearing test?
No. It is not a medical test, it is uncalibrated and it says nothing about whether your hearing is normal. If your hearing drops suddenly, see a doctor the same day.
Why does my curve differ from the standard one?
Mostly because of your headphones and how they fit. The unknown level of your reference tone, headphones instead of a free sound field, your individual ears and the matching error add to it.
What exactly is a phon?
The loudness level in phons equals the level in dB SPL of an equally loud 1 kHz tone. For a 1 kHz tone both numbers are the same.
Why did I get “limit reached”?
The page never plays above digital full scale and never more than 20 dB above the level the standard predicts. Deep bass on small earphones can need more.