For representational purpose (Image by Gerd Altmann from Pixabay)
Shreyas Kannan
Plaksha University
The human ear has a maximum hearing range of 20 Hz to 20,000 Hz. However, in all reality the range at which we are most sensitive is from 1000 Hz to 4000 Hz at which most natural speech occurs. As frequency decreases, the sound energy or decibels needed to hear sounds increases, which makes the sound effectively “too soft” unless played at a high enough volume. What this means is that the lower and higher frequencies are both difficult to perceive normally, and frequencies outside of this range entirely, Infrasound, which vibrates below 20 Hz, and ultrasound, which is above 20,000 Hz, are simply imperceptible.
These imperceptible sounds however, have a very perceptible effect. Vic Tandy, a British engineer, believed his laboratory was haunted—until he discovered that a silent 19 Hz sound wave, produced by a fan, was resonating with his eyeballs and triggering shadowy hallucinations. Even though these sounds were below the threshold of human hearing, it could still alter mood, physiology, and cognition.
Infrasound and ultrasound can also have indirect subliminal effects. They can very subtly and over long durations of time have a negative or positive effect on the psyche of the listener. Infrasound, although inaudible, can cause a range of adverse effects, including fatigue, sleep disturbance, and cognitive dysfunction.
How does this work, especially for sounds we can’t even hear? The sounds in the Ultrasonic range tend to stimulate the emotional centers of the brain, which generally are the amygdala and hippocampus, to name a few. A study proceeded to track this and found that sounds containing inaudible high-frequency components induced activation in deep brain structures associated with emotion and reward. This effectively demonstrates a reflexive unconscious emotional response, be it positive or negative, toward a specific band of sound frequencies.
The issues do not end here. There is a persistent worry of chronic exposure to just basic sound, not just ultrasonic or infrasonic sound, having long term effects on the brain. Symptoms such as ‘chronic fatigue,’ ‘repeated headache,’ and ‘backache’ are observed to be highly associated with low- and mid-octave band center frequency noise exposure among the sampled workers. Among the major psychological symptoms... It is evident that ‘irritability’ is highly associated with low- and mid-octave band noise frequency characteristics. In conclusion even when the noise isn't painfully loud, its frequency can still degrade physical and mental health over time which should be raising ethical and public health concerns.
These effects, as can be surmised, are highly weaponizable “smart consumer devices produce possibly imperceptible sound at both high (17–21kHz) and low (60–100Hz) frequencies, at the maximum available volume setting, potentially turning them into acoustic cyber-weapons.”
The physical and systemic effects that can be caused by long exposure to something that can technically originate from our devices, especially considering previously what the Infrasonic and ultrasonic bands can potentially do. Overall, we find that many of the devices tested are capable of reproducing frequencies within both high and low ranges, at levels exceeding those recommended in published guidelines. Such attacks are often trivial to develop and, in many cases, could be added to existing malware payloads, as they may be attractive to adversaries with specific motivations or targets.
One particular patent actually claims that 1/2 Hz frequency (Around 0.5 Hz) affects the autonomic nervous system and can produce a variety of effects, not limited to Eyelid drooping (ptosis) Relaxation and drowsiness Feeling of pressure on the forehead Visual effects with eyes closed Stomach sensations Tenseness (at certain frequencies). It goes on to propose how this can be used in law enforcement in the form of Non-lethal crowd control Creating disorientation in standoff situations and Remote manipulation from a distance. It goes on to list the effects of the 2.5 Hz range and the other set of effects this has.
However, not all sound effects are bad. Certain ways of application of sound can be used to actually help treat mental issues. One example is through the use of binaural beats, a form of imperceptible or subtle auditory stimulation, which are being studied for their effects on mood regulation, anxiety, and depression. Binaural beats are a type of sound that can influence brainwave activity by playing two slightly different frequencies in each ear, creating a perceived third “beat” in the brain in the way of a non-invasive sound-based intervention. A systematic study conducted to this end found positive effects in the short term while stressing that further research was needed in the long term to determine the full scope of positive effects.
It should also be noted that while these frequencies can be used negatively, it is perfectly possible for them to be used positively. Playing the right type of sound, be it music or a particular frequency set at a volume too low to be heard tended to elicit a positive response on mood and well being.
From the different sources of literature and patent claims, it can be surmised that with the exact know-how and mapping of which exact frequency to use to affect a person in a certain manner, one could be completely manipulated to actually feel a certain way about a topic that we might actually dislike. Any emotion can be aroused as necessary. Furthermore, it can be done through the speakers in everyday devices! An advertisement for a product could play the right sounds to make you view it more favourably, documentaries could potentially use this to make you feel particularly worse about a certain topic to increase the impact, electoral candidates can subtly change their image playing the right sounds at the right time, interviewees could potentially be influenced to feel uneasy for no ‘explainable’ reason as a form of sabotage, etc! The actual potential for abuse of the sounds we cannot even hear, is extreme.
How can we protect ourselves from these phenomena? The answer is quite difficult, especially at this age where sounds come from everywhere around us. The solution to this is to call for scientific transparency, proper protocols to monitor the actual playing sounds and strictly maintaining awareness of one's surroundings. In this day and age we must learn to listen to sounds that we cannot hear.
Shreyas Kannan is a B.Tech student in Robotics and Cyber-Physical Systems (RCPS) at Plaksha University, and part of its inaugural graduating batch. He has an ardent passion for all things related to movement and propulsion in vehicles, and brings boundless curiosity and energy to projects that make objects move—whether on land, underwater, or in space. From autonomous underwater navigation to aerospace systems, Shreyas is eager to explore and contribute to the frontier of motion-driven technologies.
