The brown note is a theoretical infrasound frequency that would cause humans to lose control of their bowels due to resonance. There is no scientific evidence to support the claim that a "brown note" (transmitted through sound waves in air) exists.
The name is metonymy for the color of normal 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.
The brown note was tested on the television show MythBusters using 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 twelve enclosures at MythBusters had been specially modified for deeper bass extension. The Meyer Sound team, under the direction of Schwenke and John Meyer, devised a special test and measurement system in order to test the theory at levels far beyond that experienced at any concert, and at far lower frequencies. Twelve 700-HP ultrahigh-power subwoofers had their input cards modified to allow deep subsonic frequencies, and their ports plugged to prevent a loss of efficiency at frequencies below their normal operating range. The modified cabinets were then stacked three high and faced inward in an open ring configuration. Test signals were generated by a SIM 3 audio analyzer, with software modified to produce tones down to 5 Hz. A precision B&K sound level analyzer fed by a model 4189 microphone and ZF 0023 attenuator measured levels. The experimenters on the show tried a series of frequencies between 5 and 10 Hz at a level of 120–153 decibels of sound pressure, but they were unsuccessful in producing the rumored effects. 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.
Another show, Brainiac: Science Abuse, claimed to have performed an experiment using 22.275 Hz at −30 dB (according to the show's producers used by Japan's police and tested by the French military). During the program, they broadcast the note over the air (and into the living rooms of viewers) in an attempt to cause bowel movements among those who had chosen to stay in the room despite repeated warnings and opportunities to leave. It should be noted, however, that sound at this frequency at a significant volume cannot be generated by television speakers, nor by most subwoofers, nor by the cassette-tape boombox used to generate the note for the test subject. They also alleged to have confirmed the myth with a subject, but this subject was out of camera shot for all of the piece except at the very beginning.
Loud concert levels of subwoofer arrays have been cited as causing lung collapse in individuals who are very close to the subwoofer, especially for smokers who are particularly tall and thin.
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.