- For similar phrases, see Brown note (disambiguation).
The brown note is a hypothetical infrasonic frequency that would cause humans to lose control of their bowels due to resonance. Attempts to demonstrate the existence of a "brown note" using sound waves transmitted through air have failed.
The name is a metonym for the color of human feces. Frequencies supposedly involved are between 5 and 9 Hz, which is below 20 Hz, the lower frequency limit of human hearing. High power sound waves below 20 Hz are felt in the body, not heard by the ear as sound. The only other vibrations titled with colors are the colors of noise and blue notes.
Television show tests 
Television show MythBusters used twelve Meyer Sound 700-HP subwoofers—a model and quantity that has been employed for major rock concerts. Normal operating frequency range of the selected subwoofer model was 28 Hz to 150 Hz but the 12 enclosures at MythBusters had been specially modified for deeper bass extension. Roger Schwenke and John Meyer directed the Meyer Sound team in devising a special test rig that would produce very high sound levels at infrasonic frequencies. The subwoofers' tuning ports were blocked and their input cards were altered. The modified cabinets were positioned in an open ring configuration: four stacks of three subwoofers each. Test signals were generated by a SIM 3 audio analyzer, with software modified to produce infrasonic tones. A Brüel & Kjær sound level analyzer, fed with an attenuated signal from a model 4189 measurement microphone, displayed and recorded sound pressure levels. The experimenters on the show tried a series of frequencies as low as 5 Hz, attaining a level of 120 decibels of sound pressure at 9 Hz and up to 153 dB at frequencies above 20 Hz, but the rumored physiological effects did not materialize. The test subjects all reported some physical anxiety and shortness of breath, even a small amount of nausea, but this was dismissed by the participants, noting that sound at that frequency and intensity moves air rapidly in and out of one's lungs.
Physiological effects of low frequency vibration 
In September 2009, London student Tom Reid died of sudden arrhythmic death syndrome (SADS) after complaining that 'loud bass notes' were 'getting to his heart'. The inquest recorded a verdict of natural causes, although some experts commented that the bass could have acted as a trigger.
Air is a very inefficient medium for transferring low frequency vibration from a transducer to the human body. Mechanical connection of the vibration source to the human body, however, provides a potentially dangerous combination. The U.S. space program, worried about the harmful effects of rocket flight on astronauts, ordered vibration tests that used cockpit seats mounted on vibration tables to transfer "brown note" and other frequencies directly to the human subjects. Very high power levels of 160 dB were achieved at frequencies of 2–3 Hz. Test frequencies ranged from 0.5 Hz to 40 Hz. Test subjects suffered motor ataxia, nausea, visual disturbance, degraded task performance and difficulties in communication. These tests are assumed by researchers to be the nucleus of the current urban myth.
The report "A Review of Published Research on Low Frequency Noise and its Effects" contains a long list of research about exposure to high-level infrasound among humans and animals. For instance, in 1972, Borredon exposed 42 young men to tones at 7.5 Hz at 130 dB for 50 minutes. This exposure caused no adverse effects other than reported drowsiness and slight blood pressure increase. In 1975, Slarve and Johnson exposed four male subjects to infrasound at frequencies from 1 to 20 Hz, for 8 minutes at a time, at levels up to 144 dB SPL. There was no evidence of any detrimental effect other than middle ear discomfort. Tests of high-intensity infrasound on animals resulted in measurable changes, such as cell changes and ruptured blood vessel walls.
See also 
- Acoustic resonance
- The Mosquito, a commercial device that deters loitering by emitting sound with a very high frequency
- "World Wide Recorder Concert", a South Park episode which features the brown note as a plot element
- "Brown Note". Meyer Sound. 2000. Retrieved 2006-08-30.
- Meyer Sound 700-HP UltraHigh-Power Subwoofer datasheet
- "Meyer Sound Gets Down to Basics in MythBusters Episode". Meyer Sound Laboratories. September 2004. Retrieved September 1, 2010.
- The Pentagon considers ear-blasting anti-hijack gun — New Scientist
- Wired. Music Fans, Beware the Big Bass
- Loud bass music ‘killed student’ Tom Reid, Metro, retrieved 18 June 2010
- Tempest, W. Infrasound and low frequency vibration (1977). Academic Press Inc. (London) Ltd
- ProSoundWeb: some effects of low end (bulletin board entry by Tom Danley)