Here is an explanation of the Fletcher-Munson effect for live sound engineers:
The Fletcher-Munson effect refers to how the human ear perceives sound levels differently at different frequencies. Specifically, our ears are less sensitive to low and very high frequencies compared to mid-range frequencies.
This means that when listening to a sound with the same intensity across all frequencies, the mid-range will sound louder to us than the low and high end. For example, a 1 kHz tone might need to be only 60dB SPL to sound loud, but a 50Hz or 15kHz tone would need to be 80dB SPL to seem as loud.
In live sound, this effect means you often need to boost low and high frequencies more than mid-range to achieve a balanced mix. If you don’t compensate for the Fletcher-Munson effect, your mix may end up sounding thin or weak in the bass and treble.
To offset this:
- Carefully EQ sections like kick, bass, and cymbals to taste
- Use high/low shelving EQs rather than peaking EQs
- Boost highs more for listeners farther from the stage
- Consider shaping vocals, guitars, and keys around 2-5 kHz for clarity
- Reference your mix on different systems to check the tonal balance
Understanding how our ears work allows sound engineers to create mixes that sound full, balanced, and clear for the audience. The Fletcher-Munson effect is a key psychoacoustic principle that guides proper live sound equalisation.
Harvey Fletcher and Wilden A. Munson
Here’s some background on Fletcher and Munson:
Harvey Fletcher and Wilden A. Munson were researchers who conducted pioneering psychoacoustic experiments in the 1930s. They published a seminal paper in 1933 titled “Loudness, its definition, measurement and calculation”.
In their research, Fletcher and Munson determined that the human ear perceives different frequencies at different loudness levels. They measured test subjects’ hearing sensitivity across the audio spectrum to define equal-loudness contours – curves that connect points of equal perceived loudness at different frequencies.
These contours demonstrated that people hear mid-range frequencies louder than low or high frequencies at the same amplitude. This phenomenon became known as the Fletcher-Munson effect or Fletcher-Munson curves.
Harvey Fletcher (1884–1981) was an American physicist and known as the “father of stereophonic sound”. He conducted early work on telephone transmission at Bell Laboratories and speech perception.
Wilden A. Munson (1903-1976) was an American psychologist and researcher. He collaborated with Fletcher on multiple psychoacoustic studies while working as a professor at Ohio State University.
The findings of Fletcher and Munson formed the basis for much of what we know about human hearing and auditory perception. Their equal-loudness contours are still used as a reference today, with some modern revisions. But the underlying principles they uncovered remain relevant in fields like audio engineering.
So in summary, Fletcher and Munson were pioneering scientists whose psychoacoustic research revealed how human hearing changes with frequency and intensity, which helped shape modern understanding of acoustics and sound.