Golden Gate Bridge Main article: Golden Gate Bridge

The Golden Gate in California, as seen from the Marin Headlands looking south.

The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, the opening of the San Francisco Bay onto the Pacific Ocean. As part of both US Highway 101 and California Route 1, it connects the city of San Francisco on the northern tip of the San Francisco Peninsula to Marin County.

The Golden Gate Bridge was the longest suspension bridge span in the world when completed in 1937, and is an internationally recognized symbol of San Francisco and California in general. Since its completion, the span length has been surpassed by eight other bridges. It still has the second longest suspension bridge main span in the United States, after the Verrazano-Narrows Bridge in New York City. In 2007, it was ranked fifth on the List of America’s Favorite Architecture by the American Institute of Architects.

Nautical transportation

The Golden Gate strait serves as the primary access channel for nautical travel to and from the San Francisco Bay, one of the largest cargo ports in the United States. Commercial ports includes the Port of Oakland, the Port of Richmond, and the Port of San Francisco. Commercial cargo ships use the Golden Gate to access the San Francisco Bay, as well as barges, tankers, fishing boats, cruise ships, and privately owned boats, including wind-surfers and kite-boards. About 9000 ships moved through the Golden Gate in 2014, and a similar amount in 2015.^[9] The U.S Coast Guard maintains a Vessel Traffic Service to monitor and regulate vessel traffic through the Golden Gate.^[10]

For navigational guidance, there are white and green lights on the center of the span of the Golden Gate Bridge.^[11] Lighthouses with beacons and foghorns provide alerts at Point Bonita, Point Diablo, Lime Point and Mile Rocks. Before the Golden Gate Bridge was built, a lighthouse protected the south side of the strait at Fort Point. Buoys and radar reflectors provide additional navigational aid at various locations throughout the strait.^[12]

New World War – Revolutionary Methods for Political Control

Sonic Weapons
Introduction

A variety of high powered sonic weapons (SW) exist spanning the infrasonic, ultrasonic, and audible ranges. Because they are weapons which direct sound onto a target, and sound is energy, they can be considered directed-energy weapons.

These weapons produce both psychological and physical effects. They include highly directional devices which can transmit painful audible sound into an individual’s ear at great distances and infrasonic generators which can shoot acoustic projectiles hundreds of meters causing a blunt impact upon a target.

Infrasonic generators can cause negative emotions such as fear, anxiety, or depression, as well as biological symptoms like nausea, vomiting, organ damage, burns, or death—depending on the frequency and power level. Most of these weapons function between the frequency range of about 1 Hz to 30 kHz. These frequencies occur within the following waves: Extremely Low Frequency (ELF) 1 Hz to 30 Hz, Super Low Frequency (SLF) 30 Hz to 300 Hz, Ultra Low Frequency (ULF) 300 Hz to 3 kHz, and Very Low Frequency (VLF) 3 kHz to 30 kHz.1

Within the ELF region of the spectrum, there is a type of sound called infrasound, which occurs between 3 and 20 Hz. Infrasound is usually not heard, but it can be if the power level is sufficient. Next, audible noise begins for most people from about 20 Hz up to 20 kHz, and occurs between the upper ELF into the VLF ranges. Ultrasound begins in the VLF range at about 20 kHz, just above human hearing.

Another sound factor is power, usually described using a unit of measurement called a decibel. Decibels are used to measure the power of audible and inaudible sound, both of which produce effects. Any sound begins to become physically painful at about 120 decibels, although at lower levels it can cause discomfort. At about 130 decibels it becomes unbearable. In this chapter, words such as intensity, level, power, pressure, and decibel, are all used to describe sound power.

ResonanceAll of the chemical reactions in the cells of living organisms are caused by the electromagnetic oscillations, pulsations, and vibrations, which are collectively referred to as vibrational frequencies. All physical matter is vibrating at its own vibrational frequency.

Resonance occurs when a connection is made between a source and a target which are vibrating at the same frequency. When this happens, the materials become joined and are said to be resonating. Once resonance has been achieved, an energy exchange takes place on the surface of the membrane of each cell. If the source of energy is more powerful, it directly impacts the targeted material resulting in a biological reaction.

Both infrasound and ultrasound are capable of producing resonance. This link can be established in the audible or inaudible sound ranges. A natural example of this harmonious synchronicity is frogs that sing in chorus. Mechanical examples include the pendulums of multiple clocks on the same wall which all swing in the same manner, or the string of a piano which vibrates after the same note is played on a nearby guitar.

Some organic and inorganic objects can function as resonance chambers. These objects are usually enclosures with a small opening. For instance, a glass or bottle will act as one. On a larger scale, the chest/abdominal area of the human body functions as a resonance chamber. Even an entire room with an open door or window can be used as a resonance chamber. Sound can be used to shatter or explode objects after resonance has been achieved.

Resonance can be induced electromagnetically by an infrasonic pulse generator, which can establish a link, for instance, to a person’s inner organs by resonating it in their chest area. Once this connection occurs, the power level of the generator can be increased, which would automatically transfer the energy to the person. If the power level is moderate, the person may experience pain in the chest area, or their organs may vibrate. Increasing the power level will destroy their organs.

Infrasonic and Ultrasonic WeaponsInfrasonic and ultrasonic generators, also called emitters, and VLF modulators, are weaponized devices consisting of a directional antenna dish, which can send acoustic pulses to a general or a specific are. In 1972 France was using infrasonic generators which operated at 7 Hz on its civilian population.

And by 1973 the Squawk Box was used by the British Army in Northern Ireland. It was a directional weapon that could target specific individuals by producing audible sound at about 16 kHz, which turned into infrasound at 2 Hz when it coupled with the ears.

In the early 1990s Russia had developed a 10 Hz VLF modulator capable of targeting individuals over hundreds of meters, causing pain, nausea, and vomiting. It was adjustable up to lethal levels. Since at least as far back as 1997, the US DOD has had an interest in creating generators in the infrasonic and ultrasonic ranges of 7 Hz and 20-35 kHz, respectively, which can cause these effects.

Such a device could also target the brain. These changes in brain frequencies cause changes in brain chemistry, which then influence thoughts and emotions. Furthermore, transmitting directed-energy using an exact frequency and modulation will trigger a precise chemical reaction in the brain, which, in turn will produce a specific emotion in the targeted individual.2

InfrasoundInfrasound occurs within the ELF range from a few hertz up to about 20 Hz, which is the lower limit of human hearing. Normally the power of sound rather than the frequency determines the pain and damage threshold. However, from 1 to about 250 Hz the pain/damage threshold seems to increase with frequency as well as power.

So, within this range, if the power level remains the same, but the frequency is increased, more damage can occur. Other than that, power is the critical factor which causes the damage, while the frequency determines what type of damage occurs.

Infrasound travels great distances and easily passes through most buildings and vehicles. It is normally sensed by the ears, but at high power levels it can couple with the body and be felt as vibrations.

Natural examples of this include: avalanches, earthquakes, volcanoes, and waterfalls. Whales, elephants, hippopotamuses, and rhinoceros use infrasound to communicate over great distances which includes hundreds of miles for whales. An electronic example would be a large sub-woofer. Infrasound is said to be superior to ultrasound because it retains its frequency when it couples with the human body.

From about 100 to 140 decibels infrasound causes a variety of biological symptoms depending on the frequency and power level. Basically, the higher the power level, the greater the damage. The effects include: fatigue, pressure in the ears, visual blurring, drowsiness, imbalance, disorientation, vibration of internal organs, severe intestinal pain, nausea, and vomiting. Higher power levels can liquefy bowels, and resonate the internal organs causing death. Infrasound can also cause feelings of pressure in the chest, choking, irregular breathing patterns, and respiratory incapacitation.

High powered, low frequency sound from about 30 Hz to about 100 Hz (just beyond infrasound) causes the following biological effects: fatigue, blurred vision, bowel spasms, pain or damage to internal organs, feelings of fullness in the chest cavity, chest wall vibration, difficulty breathing, difficulty swallowing, choking, and respiratory impairment.

Infrasound causes a variety of psychological effects depending on the frequency and power level. It can cause the following: loss of concentration, disgust, apathy, sadness, depression, fear, anxiety, and panic attacks. “These transmissions” said John Alexander in his December 1980 article, The New Mental Battlefield, “can be used to induce depression or irritability in a target population.”

According to the Acoustic Weapons Prospective Assessment article, which appeared in the volume 9, 2001 issue of Science and Global Security, infrasound can produce localized earthquakes. A large room within a building can act as a resonance chamber to upset the foundation causing a miniature earthquake.

UltrasoundSound that occurs beyond human hearing (about 20 kHz) is considered ultrasound. Animals such as dogs, cats, dolphins, and bats can hear ultrasound. Some whales and dolphins use ultrasound to detect their prey and as a weapon to stun them. It is said to be less effective as a weapon because it doesn’t retain its frequency when it couples with matter such as a human body.

Ultrasonic weapons produce a variety of effects depending on the power level and frequency. Many are the same as those produced by infrasound, plus heating and burning. They include: tickling in the mouth/nose area, discomfort, heating of the skin, nausea, abdominal pains, and vomiting. At higher decibels it causes burns and heating of body up to lethal temperatures. Another very painful effect is bone resonation, which could cause a person’s bones to literally explode.

“Aimed at the head, the resonating skull bones have caused people to hear voices,” revealed the Federation of American Scientists in their 1997 article, Non-Lethal Weapons for Military Operations other than War.

Sonic ProjectilesThe same ELF modulators previously mentioned, which cause a variety of biological and psychological effects, can also function as emitters of infrasonic and ultrasonic projectiles.3

These weapons are basically sonic rifles and canons which can transmit invisible energy over hundreds of meters, causing a blunt impact. The Nazis are said to have developed a sonic cannon capable of shooting down allied bombers. In the early 1990s Russia had created a 10 Hz sonic cannon, which consisted of an infrasonic generator connected to a radar dish. It transmitted invisible projectiles the size of a baseball hundreds of meters affecting a blunt force on a target.4

It could also be adjusted to cause effects ranging from physical discomfort up to death. Effects short of death included abdominal pains, nausea, and vomiting. In addition, it could cause a person’s bones to resonate, which is extremely painful.

The 1997 FAS report described that the US was developing such a weapon to cause these exact same effects. Then on July 16, 2002, ABC News announced in their Sonic Bullets Acoustic Weapon of the Future report, that the US Military had in its possession a sonic cannon. “This new technology,” they declared, “is likely to affect almost every aspect of our lives, in ways we can only begin to imagine.”

Vortex GunThe Vortex Launcher, (also called the Vortex Canon, Wind Canon, and Shockwave Weapon), is capable of transmitting an invisible whirlwind of force to effect a considerable blunt impact on a target.

It can also be used to transmit chemical irritants to a specific individual or group. It will allegedly be used to disable or destroy personnel such as enemy combatants or disruptive crowds. Most of the current information pertaining to this technology is classified. But in the late 1990s the US Military is said to have developed a vortex gun in conjunction with various defense contractors, the US Army Research Laboratory, and Pennsylvania State University.

It has a distance of at least 50 meters. The UK, Russia, and Germany have also expressed interest in this technology. This weapon dates back to World War II when an Austrian-born Nazi scientist, Dr. Zippermeyer, invented a device known as the Wind Cannon (windkanone) intended to shoot down Allied bombers.

It was an explosion-driven vortex capable of transmitting a high-velocity whirlwind of smoke at least two hundred meters. It consisted of a combustion chamber the size of a building which generated the explosion, and a specialized nozzle at the end of a tube attacked to the chamber, which formed the vortex.

In addition to the explosion-driven method previously mentioned, the air pressure which passes through the nozzle can also be produced by an infrasonic generator. Although the projectile can be generated acoustically, the actual energy projectile which collides with a target consists of air or gas.5

After the air is generated, it exits the chamber through a special nozzle that forms the vortex. It works in the following way: As the burst of air exits, the air in the center of the nozzle moves much faster than the air on the sides, so it curves around from the center to the outer edges and forms a fast-moving circular air current (a vortex). A natural example of this is a tornado or the smoke ring of a cannon.

As far as movement is concerned there are a couple of considerations. First, the speed at which the whirlwind rotates, plus the speed at which it travels to its target. Both contribute to the blunt force effect upon the target. The faster the whirlwind itself rotates the more stable and solid the vortex. The vortex can be transmitted slowly, similar to the way a tornado whirling at two hundred miles an hour moves across the landscape at only a few miles an hour. Or it can reach its target very quickly.6 A vortex can hold chemicals, which it can accurately deliver over a great distance.

A vortex can be composed of smoke, steam, or just air. Because smoke and steam are lighter than air, they allow for a more stable vortex. But an efficient vortex can be made using just air. Normally, a burst of air passing through the atmosphere is impeded by friction and quickly loses its momentum. But because the outer edges of the vortex are circulating very fast, an almost frictionless environment is created around it, which allows it to freely glide along great distances. It strikes with the force of a solid object and can even bounce off structures and continue in a different vector.

Electromagnetic Personnel Interdiction ControlThe Electromagnetic Personnel Interdiction Control (EPIC) is a portable acoustic weapon created by Invocon Incorporated. The US Navy describes this as a developing technology which interferes with a person’s equilibrium by sending acoustic pulses of energy which disrupt the chemical and mechanical processes of the vestibular system.

The vestibular system is a part of the inner-ear that determines how sound and positions are processed by the brain. So this results in disorientation, confusion, extreme motion sickness, and vomiting. The Navy declared that the weapon will operate through walls and other protective mediums that now provide cover for combatants in urban warfare situations.

Long Range Acoustic DeviceThe Long Range Acoustic Device (LRAD), also called the Sound of Force Protection, was developed by American Technology Corporation (ATCO). There are several models including the 1000, 500, RX, and X.

The weapon emits a tightly-focused beam of audible sound to an individual or group at up to 1 kilometer. A focused beam, which can be transmitted directly into an individual’s ear, would be inaudible to others in the area. While the exact frequency is unknown, it has a power level of up to 150 decibels. It is weather resistant, lightweight, has a low power consumption, and very portable. It can be equipped with an autonomous tracking feature.

The weapon can transmit MP3 sound files, an ear-splitting warning tone, or an operator’s voice which can be automatically translated into a different language. Its intended uses include, area denial and crowd control. According to its manufacturer, it is to be used for behavior modification and psychological operations. Reportedly, at high power levels it can cause loss of equilibrium, migraines, nausea and vomiting. It is now in use by the military.

Directed Stick RadiatorThe Directed Stick Radiator (DSR), a creation of American Technology Corporation, is a small portable acoustic weapon, which fires a focused, painful, audible sound up to 100 yards. It is a 1-meter long, battery operated stick made of polymer. It operates in the 10 kHz region, and is adjustable up to 140 decibels.

The device contains a series of internal electric disks that function as amplifiers. It works in the following manner: An electrical signal is sent to the first disk in the rear, which sends a pressure pulse to the next disk, which amplifies the pulse, then passes it along to be amplified by the next disk. This process of amplification continues until the pulse exits the weapon. “It shoots out a pulse of sound that’s almost like a bullet,” described Elwood Norris, ATC’s chairman.

The weapon can transmit speech and other sounds. It can also act as a directional microphone in reverse operation. According to its manufacturer, its kinetic effect is so intense that it can knock someone back and cause migraine headaches. Business Wire and the BBC have stated that in addition to being used to remotely incapacitate a specific individual it will be used for psychological operations.

A similar device is the person-portable Sonic Firehose developed by SARA. It can allegedly knock people to the ground by transmitting a high-decibel sound up to 1 kilometer. Universal Guardian Holdings has developed the Acoustic Defender which can deliver debilitating sound at up to 100 yards.

7 Amazing Things You Can Do With Sound Waves
By Laura Kiniry – Mar 17, 2014

I included the above information about sound as a weapon because I believe it is quite possible that they are employing the FOG HORNS on the Golden Gate Bridge to cause the GOLD in the earth around the OROVILLE DAM to shake loose and be free to be revealed and recovered when the water rushes over the land at the bursting of the dam. Pay close attention to the information about the Fog Horns. In these articles, you will learn that the Fog Horns are not really necessary, that there is a great deal of variance as to how long and how often the are sounding and sometimes for days straight, you will see a posting all about how sound affects things and what frequencies, decibels and vibrations can do. We KNOW that sound affects us physically, emotionally and Spiritually. I KNOW it has a huge impact on the environment as well. Just saying…

Golden Gate District

golden gate bridge: fog horns by James Torrance

golden gate bridge: fog horns by James Torrance published on 2012-09-19T21:34:46Z recorded in the early hours of the morning from a window in cavallo point, approximately half a mile north of the bridge. september 2012

Click the link to hear the foghorns: https://soundcloud.com/jamest/golden-gate-bridge-fog-horns

Painted the same industrial orange as the bridge, the horns are either 2 or 3 feet long and flare out to a bell either a foot or 18 inches in diameter. The bell resembles an old phonograph.

Foghorns at Mid-Span

There are three foghorns mounted below the roadway level at mid-span on the Golden Gate Bridge. One faces east and is 24-1/2 inches long and the horn bell is 11-inches in diameter. Two face west and are each 36-inches long with a horn bell that is 18-inches in diameter. The three horns sound as two blasts, each with a distinct tones. The lower of the two tones blasts to the west.

The sequence of the two blasts is this: A 9-second pause starts the sequence and is followed by a 1-second foghorn blast, a 2-second pause, a 1-second blast, a 36-second pause, a 1-second blast, a 2-second pause, a 1-second blast, and a 36-second pause. This pattern continues when the fog horns are on.

In addition to the traditional foghorns on the bridge, there are 22 electronic fog signals around the bay that are controlled by the Coast Guard. Their sound is an unromantic ping or beep. Only a foghorn on the Golden Gate Bridge sounds like a foghorn.

In the late 1970’s, one of the original 1937 foghorns stopped working when its two air valves gave way and the two-tone horn became a one-tone horn. Since the mechanism was so old, replacement parts were impossible to find. The hobbled horn continued to sound with just one-tone until 1985, when the original foghorns were replaced by new one manufactured by the Leslie Air Horn Company. The new single-tone horns differ in frequency or tone from each other, but operate with compressed air, just like the originals.

Foghorns at the South Tower Pier

There are two foghorns mounted on the south tower pier, about 40 feet above the waterline. One faces east and one faces west. Each horn is 48-inches long with a horn bell that is 23-1/2 inches in diameter.

The two foghorns sound at the same time as a single tone and blast, in this sequence: A 2-second blast, an 18-second pause, a 2-second blast, and an 18-second pause. This pattern continues as long as the horns are turned on.

The foghorns on the south tower pier are one-tone and have a lower sound than the mid-span horns. Source

Fog and the Golden Gate Bridge

The Golden Gate Bridge has an influence in directing fog as it pushes up and pours down around the Bridge. “Advection fog” forms when humid air from the Pacific Ocean swoops over the chilly California current flowing parallel to the coast. The fog hugs the ground and then the warm, moist air condenses as it moves across the bay or land. This is common near any coastline. Sometimes, high pressure squashes it close to the ground. By the way, the color of the Bridge is International Orange and was chosen in part because of its visibility in the fog.

To aid in the safe travel of vessels as they pass under the Golden Gate Bridge, fog horns have been mounted on the Golden Gate Bridge since its opening in 1937. The fog horns are located in two distinct locations: at the middle of the Bridge (mid-span) and at the south (San Francisco) tower pier.

The Golden Gate Bridge fog horns have guided hundreds of thousands of vessels safely through the Golden Gate Strait, and forewarned San Franciscans when fog was rolling in to envelop the City. The fog horns operate, on average over a year, about two and a half hours a day. During March, you’ll hear them for less than half an hour a day. However, during the Bay Area’s foggy season, which typically occurs during the summer months, they can sound for over five hours a day or for days at a time.

United States Coast Guard, Waterways Management Branch sets the tones and timing pattern of the fog horns. Each fog horn has a different pitch and marine navigational charts give ships the frequency, or signature, of each fog horn.

When the fog rolls in under the Bridge roadway limiting visibility for passing ships, the fog horns are manually turned on (and off) by Bridge workers.

The Physics Classroom » Physics Tutorial » Sound Waves and Music » Pitch and Frequency

Sound Waves and Music – Lesson 2 – Sound Properties and Their Perception

Pitch and Frequency from the Physics Classroom (grades 6 to adult)
This lesson describes how sound pitch is related to the frequency of the vibrations, which is helpful in understanding the science behind the different tones of the foghorns on the Golden Gate Bridge

Pitch and Frequency

A sound wave, like any other wave, is introduced into a medium by a vibrating object. The vibrating object is the source of the disturbance that moves through the medium. The vibrating object that creates the disturbance could be the vocal cords of a person, the vibrating string and sound board of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker. Regardless of what vibrating object is creating the sound wave, the particles of the medium through which the sound moves is vibrating in a back and forth motion at a given frequency. The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. The frequency of a wave is measured as the number of complete back-and-forth vibrations of a particle of the medium per unit of time. If a particle of air undergoes 1000 longitudinal vibrations in 2 seconds, then the frequency of the wave would be 500 vibrations per second. A commonly used unit for frequency is the Hertz (abbreviated Hz), where

1 Hertz = 1 vibration/secondAs a sound wave moves through a medium, each particle of the medium vibrates at the same frequency. This is sensible since each particle vibrates due to the motion of its nearest neighbor. The first particle of the medium begins vibrating, at say 500 Hz, and begins to set the second particle into vibrational motion at the same frequency of 500 Hz. The second particle begins vibrating at 500 Hz and thus sets the third particle of the medium into vibrational motion at 500 Hz. The process continues throughout the medium; each particle vibrates at the same frequency. And of course the frequency at which each particle vibrates is the same as the frequency of the original source of the sound wave. Subsequently, a guitar string vibrating at 500 Hz will set the air particles in the room vibrating at the same frequency of 500 Hz, which carries a sound signal to the ear of a listener, which is detected as a 500 Hz sound wave.

The back-and-forth vibrational motion of the particles of the medium would not be the only observable phenomenon occurring at a given frequency. Since a sound wave is a pressure wave, a detector could be used to detect oscillations in pressure from a high pressure to a low pressure and back to a high pressure. As the compressions (high pressure) and rarefactions (low pressure) move through the medium, they would reach the detector at a given frequency. For example, a compression would reach the detector 500 times per second if the frequency of the wave were 500 Hz. Similarly, a rarefaction would reach the detector 500 times per second if the frequency of the wave were 500 Hz. The frequency of a sound wave not only refers to the number of back-and-forth vibrations of the particles per unit of time, but also refers to the number of compressions or rarefactions that pass a given point per unit of time. A detector could be used to detect the frequency of these pressure oscillations over a given period of time. The typical output provided by such a detector is a pressure-time plot as shown below.

Since a pressure-time plot shows the fluctuations in pressure over time, the period of the sound wave can be found by measuring the time between successive high pressure points (corresponding to the compressions) or the time between successive low pressure points (corresponding to the rarefactions). As discussed in an earlier unit, the frequency is simply the reciprocal of the period. For this reason, a sound wave with a high frequency would correspond to a pressure time plot with a small period – that is, a plot corresponding to a small amount of time between successive high pressure points. Conversely, a sound wave with a low frequency would correspond to a pressure time plot with a large period – that is, a plot corresponding to a large amount of time between successive high pressure points. The diagram below shows two pressure-time plots, one corresponding to a high frequency and the other to a low frequency.

The ears of a human (and other animals) are sensitive detectors capable of detecting the fluctuations in air pressure that impinge upon the eardrum. The mechanics of the ear’s detection ability will be discussed later in this lesson. For now, it is sufficient to say that the human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz. Any sound with a frequency below the audible range of hearing (i.e., less than 20 Hz) is known as an infrasound and any sound with a frequency above the audible range of hearing (i.e., more than 20 000 Hz) is known as an ultrasound. Humans are not alone in their ability to detect a wide range of frequencies. Dogs can detect frequencies as low as approximately 50 Hz and as high as 45 000 Hz. Cats can detect frequencies as low as approximately 45 Hz and as high as 85 000 Hz. Bats, being nocturnal creature, must rely on sound echolocation for navigation and hunting. Bats can detect frequencies as high as 120 000 Hz. Dolphins can detect frequencies as high as 200 000 Hz. While dogs, cats, bats, and dolphins have an unusual ability to detect ultrasound, an elephant possesses the unusual ability to detect infrasound, having an audible range from approximately 5 Hz to approximately 10 000 Hz.
The sensation of a frequency is commonly referred to as the pitch of a sound. A high pitch sound corresponds to a high frequency sound wave and a low pitch sound corresponds to a low frequency sound wave. Amazingly, many people, especially those who have been musically trained, are capable of detecting a difference in frequency between two separate sounds that is as little as 2 Hz. When two sounds with a frequency difference of greater than 7 Hz are played simultaneously, most people are capable of detecting the presence of a complex wave pattern resulting from the interference and superposition of the two sound waves. Certain sound waves when played (and heard) simultaneously will produce a particularly pleasant sensation when heard, are said to be consonant. Such sound waves form the basis of intervals in music. For example, any two sounds whose frequencies make a 2:1 ratio are said to be separated by an octave and result in a particularly pleasing sensation when heard. That is, two sound waves sound good when played together if one sound has twice the frequency of the other. Similarly two sounds with a frequency ratio of 5:4 are said to be separated by an interval of a third; such sound waves also sound good when played together. Examples of other sound wave intervals and their respective frequency ratios are listed in the table below.

Interval	Frequency Ratio	Examples
Octave	2:1	512 Hz and 256 Hz
Third	5:4	320 Hz and 256 Hz
Fourth	4:3	342 Hz and 256 Hz
Fifth	3:2	384 Hz and 256 Hz

The ability of humans to perceive pitch is associated with the frequency of the sound wave that impinges upon the ear. Because sound waves traveling through air are longitudinal waves that produce high- and low-pressure disturbances of the particles of the air at a given frequency, the ear has an ability to detect such frequencies and associate them with the pitch of the sound. But pitch is not the only property of a sound wave detectable by the human ear. In the next part of Lesson 2, we will investigate the ability of the ear to perceive the intensity of a sound

Listen to the Fog Horn at Golden Gate Bridge during Sunrise

Rohit Adukia

Dec 18, 2020

Experience sunrise at the Golden Gate Bridge on a foggy summer morning. See how calmly the fog rolls in, birds fly by and the towering Golden Gate Bridge awaits the sun.