Buzz
Humans can detect sound frequencies ranging from 20 Hz to 20 kHz. Sound, a fundamental natural element, is as crucial and omnipresent as the light we perceive and the air we inhale. Whether it's melodious tunes or jarring alarms, these essential vibrations permeate our everyday experiences.
Yet, sound holds mysteries beyond what our ears can perceive. The study of acoustics unveils a world of fascination, brimming with marvels—and potential hazards.
10. The Visual Microphone
When sound strikes an object, it is typically absorbed and dispersed without visible impact. However, minute vibrations, measuring just tenths of a micrometer, ripple across the surface—imperceptible to the naked eye but detectable by high-speed cameras. Researchers from Adobe, Microsoft, and MIT have pioneered an ingenious algorithm capable of analyzing these microscopic movements to reconstruct the original audio from silent footage. Ordinary objects like tissue boxes and water glasses transform into visual microphones using this groundbreaking technology. Despite some distortion, the melody and lyrics of “Mary Had a Little Lamb” are clearly audible when extracted from recordings of a chip bag or a houseplant's leaves.
Though still in its early stages, this technology holds immense promise for precise sound retrieval, enabling advanced surveillance capabilities that surpass the constraints of traditional microphones and penetrate soundproof barriers (as long as they are transparent). The creators of the visual microphone, however, envision a less contentious application, aiming to use it for non-invasive analysis of material properties.
9. DolphinAttack
DolphinAttack is a cutting-edge technique that manipulates speech recognition systems using ultrasound frequencies, which exceed 20 kHz and are inaudible to humans (though within the range of dolphin echolocation). This stealthy method has been proven to control Siri, Cortana, Alexa, and even voice-activated navigation systems in Audi vehicles, posing a significant security threat. The potential harm ranges from dialing specific numbers to accessing harmful websites and installing malware.
A DolphinAttack hacker could effortlessly dim screens, mute audio, or activate airplane mode to aid their attack. However, the current range is limited to 1.7 meters (5.6 ft). Surprisingly, the setup is relatively simple and inexpensive, requiring only an amplifier, an ultrasonic transducer, a battery, and a speaker—such as a smartphone. As the technology evolves, voice assistants must brace themselves for the growing threat of DolphinAttack.
8. The Terror of Infrasound
While there is limited evidence that typical ultrasound impacts humans, with only unverified claims of dizziness and unease, infrasound—inaudible yet potent—can trigger profound psychological and physical effects. These low-frequency vibrations affect the entire body, inducing hyperventilation, hallucinations, panic, and depression. At 19 Hz, infrasound resonates with the human eyeball, severely distorting peripheral vision. Interestingly, a tiger’s roar emits infrasound at this frequency, a natural mechanism to disorient and terrify prey or rivals.
Infrasound, common in both nature and machinery, might explain reports of haunted locations. The famous tale, “The Ghost in the Machine,” illustrates this. Vic Tandy, a medical engineer working in a lab producing life support equipment, initially dismissed his colleagues’ stories of hauntings. However, he soon experienced mild depression and occasional chills. One night, alone in the lab, he saw a grey, silent figure appear to his left. Terrified, he turned, and the apparition vanished. The next day, Tandy discovered the “ghost” was caused by a hidden fan vibrating at 19 Hz.
7. Sonic Weapons
The concept of sonic weapons dates back to secret research by Hitler’s chief architect and minister of armaments, Albert Speer. Though never realized due to the fall of the Nazi regime, the acoustic cannon was designed to emit a concentrated, amplified sound beam capable of violently vibrating a person’s body. Anyone within 90 meters (300 ft) would face fatal consequences if exposed for over 30 seconds. Since the 1950s, military and research groups have explored sonic weapons for counterterrorism and crowd control. Depending on decibel levels, these weapons can induce nausea, incapacitating pain, disorientation, or even rupture eardrums and internal organs.
As noted earlier, infrasound, often emitted by patrolling drones, can effectively disperse rioters or demoralize enemy troops. Similarly, high-frequency ultrasound can cause fatal overheating or shatter bones through resonance. Thankfully, most such technologies are designed for non-lethal, temporary incapacitation, akin to Tasers. The US Army is currently working on a long-range acoustic weapon to deter suicide bombers and flush out Al-Qaeda operatives from their hideouts, forcing them to cover their ears in distress.
6. Herring Flatulence
During the Cold War, a Soviet submarine ventured into Sweden’s restricted naval zone, eventually running aground. The Swedes dismissed Russia’s explanation of a navigational error. In the 1980s, the Swedish Royal Navy detected mysterious underwater noises—high-pitched squeaks and pops—at night, initially attributing them to Russian submarines. Despite Soviet denials, the sounds persisted.
In 1994, Swedish Prime Minister Carl Bildt sent an angry letter to Boris Yeltsin, condemning the diplomatic violation. However, the noises continued even after the Soviet Union’s collapse, prompting Sweden to seek another explanation. Depth charges revealed only dead herring, proving the source of the disturbance was not submarines but fish.
Herring exhibit a peculiar behavior: they gulp air and release it through their anus, producing sounds known as Fast Repetitive Ticks (FRTs). Research suggests these FRTs are a form of communication, particularly during nocturnal gatherings when visibility is low. The vast herring schools in the Baltic Sea generate enough FRTs to alarm an entire nation. Sadly, Bildt never got the chance to apologize for mistaking herring social gatherings for a Russian military threat.
5. Nightingale Floors
While light moves swiftly, it has never managed to detect a ninja. Sound, however, has succeeded! Nightingale floors were ingeniously crafted as a security feature for significant Japanese structures like Nijo Castle. These floors emit loud squeaks to warn guards while mimicking the melodic chirps of nightingales for everyday use. Natural creaks from dry wooden boards were amplified by Japan’s finest artisans, ensuring assassins could never move silently through the halls of the shogun’s Kyoto residence or other vital locations. Each step rubs floor clamps against nails, producing screeches that deter even the stealthiest ninjas.
When the shogun visited, guards concealed in hidden doors would await intruders triggered by the floor’s sounds. The craftsmanship is so precise that the intruder’s location could be pinpointed by the volume of the chirps. Silent assassins faced a noisy demise. Today, tourists attempt various methods to sneak across these floors, but none have succeeded.
4. Superior Canal Dehiscence Syndrome
In 1929, biologist Pietro Tullio conducted experiments on pigeons by creating tiny holes in their semicircular canals to study sound-induced imbalance and dizziness. The inner ear is extremely fragile, and the pigeons experienced severe disorientation when exposed to loud noises post-surgery. Even the smallest defect can lead to a terrifying condition known as superior canal dehiscence syndrome. This exposes the canal to all types of sound, resulting in debilitating pain and sensations. Symptoms include tinnitus, hearing loss, hyperacusis, Tullio phenomenon (sound-induced vertigo), and the most alarming: autophony.
Autophony is the unnerving experience of hearing one’s own bodily sounds at an amplified volume, whether involuntary or not. Those affected can hear their heartbeat and even the movement of their eyes, which has been described as sounding like sandpaper on wood. Everyday activities, such as turning one’s head or walking, become excruciating. Thankfully, this rare condition affects fewer than 1% of the population, and surgical procedures can repair the damaged canal, restoring normal hearing.
3. Black Hole Decibel
The pistol shrimp, one of the loudest creatures on Earth, hunts by firing water jets so rapidly that they create bubbles. These bubbles collapse almost instantly, generating a shock wave of 210 decibels—louder than a gunshot—and reaching temperatures of 5,000 Kelvin, close to the Sun’s surface. The loudest recorded event on Earth was the 1883 eruption of Krakatoa, which obliterated 70% of the island, caused permanent hearing damage within a 160-kilometer (100 mi) radius, and echoed through the atmosphere seven times.
The final phenomenon on this list is perhaps the most monumental. In 2003, NASA detected immense sound waves from a supermassive black hole in the Perseus galaxy cluster. The sound, a cosmic B-flat 57 octaves below middle-C, is the deepest note ever recorded in the universe, over one quadrillion times lower than the range of human hearing.
While the sound from a black hole is fascinating, there’s also a theoretical sound that could create one. Generating an 1,100-decibel sound would produce waves so powerful they could distort space-time, forming a quantum singularity. Instead of massive amounts of matter collapsing, an unimaginable concentration of sound energy could compress cosmic matter into a black hole.
However, this scenario is purely hypothetical. No known medium could sustain an 1,100-decibel sound, and current technology is nowhere near capable of producing such energy. Even an advanced alien civilization, harnessing the dense fluids of an extraterrestrial atmosphere and the energy of an entire galaxy, might only theoretically achieve this ultimate feat.
2. Sound Barrier
During World War II, propeller planes faced severe performance issues as they neared the speed of sound. Shock waves caused loss of control, often leading to catastrophic crashes. The term “sound barrier” described the sudden drag and aerodynamic challenges at supersonic speeds, making it seem nearly impossible to surpass. At speeds above 1,234 km/h (767 mph), air is compressed, creating shock waves that destabilize aircraft. The advent of turbojet engines in the 1950s eventually made supersonic flight a reality.
Supersonic phenomena aren’t limited to vehicles. Bullets surpassed the sound barrier long before airplanes, though modern assassins and special forces prefer subsonic bullets paired with silencers for stealth. Even a child can create a sonic boom by popping a balloon, as the torn latex contracts at supersonic speeds. Similarly, the crack of a whip isn’t just from the tip—it’s the result of the loop’s wave motion accelerating until it breaks the sound barrier, producing sonic booms along its length.
1. Shepard Scale
Musical notes aren’t single frequencies but combinations of sound waves. This principle enables the creation of the Shepard tone, an auditory illusion. It consists of three sine waves spaced an octave apart. When played sequentially, they create a Shepard scale, giving the illusion of endlessly rising or falling pitch. As the sine waves shift, a new wave is introduced at the previous lowest pitch, tricking our brains into perceiving an infinite, seamless progression.
This captivating auditory illusion is perfect for building tension in sound effects and music. It’s famously used in The Dark Knight’s Batpod scene and Hans Zimmer’s score for Dunkirk, showcasing Christopher Nolan’s love for cinematic sound techniques.
