Sound is all around us, permeating our daily lives. We use it to communicate, enjoy music, and get alerts for incoming calls or messages. But sound can also have powerful effects on the human body and mind. Extremely loud sounds can cause pain, nausea, and even loss of consciousness. This raises an interesting question – can certain sounds literally knock a person out?
What is sound?
To understand how sound might lead to loss of consciousness, we first need to understand what sound is. Sound is made of vibrations in the air. These vibrations are waves of high and low pressure travelling away from their source. Our ears detect these waves and convert them into signals that are sent to the brain.
The characteristics of sound waves determine the sound we perceive. The amplitude (height of the wave) corresponds to the volume or loudness of the sound. The frequency (number of vibrations per second) determines the pitch. Sounds with a higher frequency are perceived as higher pitched.
Measuring sound
The volume of sound is measured in decibels (dB). Some examples:
| Whisper | 30 dB |
| Normal conversation | 60-70 dB |
| City traffic | 85 dB |
| Jackhammer | 100 dB |
| Ambulance siren | 120 dB |
As you can see from the table, loud sounds above 70 dB can start to damage hearing over time. Sounds above 120-140 dB can cause immediate harm.
How does sound affect the body?
Before looking at whether sound can lead to unconsciousness, let’s examine the other effects it can have:
Hearing loss
The most obvious impact is damage to hearing itself. Prolonged exposure to sounds over 85 dB can cause permanent hearing loss over time. Very loud sounds above 130 dB can rupture eardrums and destroy hair cells in the inner ear that detect sound waves.
Physiological stress
Exposure to loud noise has been shown to activate the sympathetic nervous system, causing a fight-or-flight response. This leads to release of stress hormones like cortisol and adrenaline. It increases heart rate, blood pressure, and metabolism.
Fatigue
Studies show background noise can have a fatiguing effect on the brain. Noise makes the brain work harder to understand speech and perform tasks. This can impair cognitive function and lead to mental fatigue.
Sleep disturbance
Not only can daytime noise be tiring, but nighttime noise can also disrupt sleep. This impairs sleep quality and the various restorative functions of sleep.
Nausea
Loud low frequencies have been associated with nausea and vertigo. Infrasound below 20 Hz can resonate with human organs and cause uncomfortable sensations.
Discomfort and pain
Sounds above 120 dB begin to cause physical discomfort and pain. The eardrums can vibrate excessively from the high pressure waves. At 150-155 dB, sound waves can rupture lung tissue.
How loud does sound need to be to cause unconsciousness?
Given the various effects of loud noise, could a powerful enough sound knock someone out? There are a few factors to consider:
Sound pressure level
Extremely loud sounds above 185 dB can physically distort the air enough to create pressure fronts that can knock a person down. But loss of consciousness is not due to the sound itself. It is caused by the shock wave violently shaking the brain within the skull.
Frequency
Low frequency infrasound below 20 Hz is more likely to cause loss of consciousness than audible noises. Infrasound can create resonance in organs at certain frequencies and potentially interfere with heartbeat.
Duration
Brief exposure to loud sound is unlikely to directly cause unconsciousness. Knockout would require prolonged exposure to fatiguing noise levels or very focused pressure waves.
Individual factors
Susceptibility to noise varies between individuals based on age, health conditions, medications, and other factors. So the same sound might knock out one person but not another.
Historical examples of sound-induced unconsciousness
There are a few dramatic examples in history of sound being used to disorient or knock out people:
The Ganzfeld effect
In the 1930s-1940s, psychologists exposed subjects to unvarying light and sound fields to cause sensory deprivation. Many reported losing touch with reality and experiencing hallucinations.
Sonic weapons
The US military is known to have developed specialized vehicles called acoustic cannons that can project intensely loud sound over distances. There are reports these have been used to disperse crowds.
Infrasound experiments
In the 1960s-70s, scientists conducted classified experiments exposing subjects to infrasound. Some reportedly caused loss of balance and unconsciousness when precisely tuned to resonate with human organs.
Is it possible to design sounds to safely knock someone out?
While very loud sounds can clearly have disorienting effects, safely rendering someone unconscious through sound alone poses challenges:
Difficulty targeting
Sound spreads out in all directions. It would be hard to target specific individuals without deafening everyone else nearby. Directional sound beams that use ultrasound have limited ranges.
Sound dissipation
Outdoors, sound dissipates quickly with distance. Indoors, sound waves reflect off surfaces. This makes controlled delivery of knockout sound waves difficult.
Danger of organ damage
Infrasound or resonance frequencies that reliably knock someone out could also risk damaging delicate organs like the eyes, brain, or lungs. More research would be needed to identify safe frequencies and exposure times.
Ethical concerns
Non-lethal acoustic weapons pose ethical risks if misused. Means of instant incapacitation without lasting harm may appeal to law enforcement yet enable abuse. Strict regulation and oversight would be imperative.
Conclusion
While very loud sounds can potentially cause disorientation and unconsciousness through fatigue, shock waves or resonance, many challenges remain in safely weaponizing sound. Any practical knockout device based on sound alone faces significant technical obstacles and ethical risks that may prove insurmountable. However, the psychoacoustic effects of sound on human physiology are complex and merit continued research.
