sound travel in water

How far does sound travel in the ocean?

The distance that sound travels in the ocean varies greatly, depending primarily upon water temperature and pressure..

Water temperature and pressure determine how far sound travels in the ocean.

While sound moves at a much faster speed in the water than in air , the distance that sound waves travel is primarily dependent upon ocean temperature and pressure. While pressure continues to increase as ocean depth increases, the temperature of the ocean only decreases up to a certain point, after which it remains relatively stable. These factors have a curious effect on how (and how far) sound waves travel.

Imagine a whale is swimming through the ocean and calls out to its pod. The whale produces sound waves that move like ripples in the water. As the whale’s sound waves travel through the water, their speed decreases with increasing depth (as the temperature drops), causing the sound waves to refract downward . Once the sound waves reach the bottom of what is known as the thermocline layer, the speed of sound reaches its minimum. The thermocline is a region characterized by rapid change in temperature and pressure which occurs at different depths around the world. Below the thermocline "layer," the temperature remains constant, but pressure continues to increase. This causes the speed of sound to increase and makes the sound waves refract upward .  

The area in the ocean where sound waves refract up and down is known as the "sound channel." The channeling of sound waves allows sound to travel thousands of miles without the signal losing considerable energy.  In fact, hydrophones, or underwater microphones, if placed at the proper depth, can pick up whale songs and manmade noises from many kilometers away.

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More information.

• Noise in the Ocean: A National Issue (National Marine Sanctuaries)
• Just how noisy is the ocean? Learn about a NOAA Effort to Monitor Underwater Sound
• Sound in the Sea Gallery
• Acoustic Monitoring

Last updated: 01/20/23 Author: NOAA How to cite this article

June 27, 2019

What Do You Hear Underwater?

A submerged science activity from Science Buddies

By Science Buddies & Sabine De Brabandere

Make waves--underwater! Learn how sound travels differently in water than it does in the air. 

George Retseck

Key Concepts Physics Sound Waves Biology

Introduction Have you ever listened to noises underwater? Sound travels differently in the water than it does in the air. To learn more, try making your own underwater noises—and listening carefully. 

Background Sound is a wave created by vibrations. These vibrations create areas of more and less densely packed particles. So sound needs a medium to travel, such as air, water—or even solids. 

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Sound waves travel faster in denser substances because neighboring particles will more easily bump into one another. Take water, for example. There are about 800 times more particles in a bottle of water than there are in the same bottle filled with air. Thus sound waves travel much faster in water than they do in air. In freshwater at room temperature, for example, sound travels about 4.3 times faster than it does in air at the same temperature.

Sound traveling through air soon becomes less loud as you get farther from the source. This is because the waves’ energy quickly gets lost along the way. Sound keeps its energy longer when traveling through water because the particles can carry the sound waves better. In the ocean, for example, the sound of a humpback whale can travel thousands of miles!

Underwater sound waves reaching us at a faster pace and keeping their intensity longer seem like they should make us perceive those sounds as louder when we are also underwater. The human ear, however, evolved to hear sound in the air and is not as useful when submerged in water. Our head itself is full of tissues that contain water and can transmit sound waves when we are underwater. When this happens, the vibrations bypass the eardrum, the part of the ear that evolved to pick up sound waves in the air. 

Sound also interacts with boundaries between two different mediums, such as the surface of water. This boundary between water and air, for example, reflects almost all sounds back into the water. How will all these dynamics influence how we perceive underwater sounds? Try the activity to find out! 

Bathtub or swimming pool (a very large bucket can work, too)

Two stainless steel utensils (for example, spoons or tongs)

Two plastic utensils

Small ball 

Adult helper

An area that can get wet (if not performing the activity at a pool)

Floor cloth to cleanup spills (if not performing the activity at a pool)

Other materials to make underwater sounds (optional)

Access to a swimming pool (optional)

Internet access (optional)

Preparation

Fill the bathtub with lukewarm water—or head to the pool—and bring your helper and other materials.

Ask your helper to click one stainless steel utensil against another. Listen. How would you describe the sound? 

In a moment, your helper will click one utensil against the other underwater . Do you think you will hear the same sound? 

Ask your helper to click one utensil against the other underwater. Listen. Does the sound appear to be louder or softer? Is what you hear different in other ways, too?

Submerge one ear in the water. Ask your helper to click one utensil against the other underwater. Listen. How would you describe this sound? 

Ask your helper to click one utensil against the other underwater soon after you submerge your head. Take a deep breath, close your eyes and submerge your head completely or as much as you feel comfortable doing. Listen while you hold your breath underwater (come up for air when you need to!). Does the sound appear to be louder or softer? Does it appear to be different in other ways? 

Repeat this sequence but have your helper use two plastic utensils banging against each other instead.

Repeat the sequence again, but this time listen to a small ball being dropped into the water. Does the sound of a ball falling into the water change when you listen above or below water? Does your perception of this sound change? Why would this happen? 

Switch roles. Have your helper listen while you make the sounds. 

Discuss the findings you gathered. Do patterns appear? Can you conclude something about how humans perceive sounds when submerged in water? 

Extra : Test with more types of sounds: soft as well as loud sounds, high- as well as low-pitched sounds. Can you find more patterns?

Extra: To investigate what picks up the sound wave when you are submerged, use your fingers to close your ears or use earbuds when submerging your head. How does the sound change when you close off your ear canal underwater? Does the same happen when you close off your ear canal when you are above water? If not, why would this be different? 

Extra: Go to the swimming pool and listen to the sound of someone jumping into the water. Compare your perception of the sound when you are submerged with when your head is above the water. How does your perception change? Close your eyes. Can you tell where the person jumped into the water when submerged? Can you tell when you have your head above the water?

Extra: Research ocean sounds and how sounds caused by human activity impact aquatic animals.  

Observations and Results Was the sound softer when it was created underwater and you listened above the water? Did it sound muffled when you had only your ear submerged? Was it fuller when you had your head submerged? 

Sound travels faster in water compared with air because water particles are packed in more densely. Thus, the energy the sound waves carry is transported faster. This should make the sound appear louder. You probably perceived it as softer when you were not submerged, however, because the water surface is almost like a mirror for the sound you created. The sound most likely almost completely reflected back into the water as soon as it reached the surface. 

When you submerged only your ear, the sound probably still appeared muffled. This happens because the human ear is not good at picking up sound in water—after all, it evolved to pick up sound in air. 

When you submerged your head, the sound probably sounded fuller. That is because our head contains a lot of water, which allows the tissue to pick up underwater sound—without relying on the eardrum. It also explains why closing your ear canal makes almost no difference in the sound you pick up while you are underwater. 

If you tried to detect where the sound came from when submerged, you probably had a hard time. Our brain uses the difference in loudness and timing of the sound detected by each ear as a clue to infer where the sound came from. Because sound travels faster underwater and because you pick up sound with your entire head when you are submerged, your brain loses the cues that normally help you determine where the sound is coming from. 

More to Explore Discovery of Sound in the Sea , from the University of Rhode Island and the Inner Space Center Can You Hear Sounds in Outer Space? , from Science Buddies Talk through a String Telephone , from Scientific American Sound Localization , from Science Buddies  Ears: Do Their Design, Size and Shape Matter? , from Scientific American STEM Activities for Kids , from Science Buddies 

This activity brought to you in partnership with Science Buddies

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How fast does sound travel through water?

Sounds travel faster through water than in air, but it takes more energy to get it going.

Sound is a wave of alternating compression and expansion, so its speed depends on how fast it bounces back from each compression – the less compressible the medium it’s travelling through, the faster it bounces back. Water is about 15,000 times less compressible than air, but it is also 800 times denser. The extra density means that the molecules accelerate more slowly for a given force, which slows the compression wave down. So water’s high density partly offsets its extreme incompressibility and sound travels at 1,493m/s, about four times faster than through air. The speed of sound in diamond is so high because it is extremely incompressible and yet relatively light.

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The basic components of a sound wave are frequency, wavelength and amplitude. In this example of a sound wave, the period of one cycle of this wave is 0.5 seconds, and the frequency of this wave is 2 cycles per second or 2 Hertz (Hz). Click image for larger view.

Click image to hear a scale of various frequencies (576 K, QuickTime). Click image for larger view.

Understanding Ocean Acoustics

Sharon Nieukirk, Research Assistant Acoustic Monitoring Project NOAA Pacific Marine Environmental Laboratory

What is Sound?

Ocean acoustics is the study of sound and its behavior in the sea. When underwater objects vibrate, they create sound-pressure waves that alternately compress and decompress the water molecules as the sound wave travels through the sea. Sound waves radiate in all directions away from the source like ripples on the surface of a pond. The compressions and decompressions associated with sound waves are detected as changes in pressure by the structures in our ears and most man-made sound receptors such as a hydrophone, or underwater microphone.

The basic components of a sound wave are frequency, wavelength and amplitude.

Frequency is the number of pressure waves that pass by a reference point per unit time and is measured in Hertz (Hz) or cycles per second. To the human ear, an increase in frequency is perceived as a higher pitched sound, while a decrease in frequency is perceived as a lower pitched sound. Humans generally hear sound waves whose frequencies are between 20 and 20,000 Hz. Below 20 Hz, sounds are referred to as infrasonic, and above 20,000 Hz as ultrasonic. The frequency of middle “C” on a piano is 246 Hz.

Wavelength is the distance between two peaks of a sound wave. It is related to frequency because the lower the frequency of the wave, the longer the wavelength.

Amplitude describes the height of the sound pressure wave or the “loudness” of a sound and is often measured using the decibel (dB) scale. Small variations in amplitude (“short” pressure waves) produce weak or quiet sounds, while large variations (“tall” pressure waves) produce strong or loud sounds.

The two examples below show sound waves that vary in frequency and amplitude.

These two waves have the same frequency but different amplitudes. Click image for larger view .

These two waves have the same amplitude but different frequencies. Click image for larger view.

The decibel scale is a logarithmic scale used to measure the amplitude of a sound. If the amplitude of a sound is increased in a series of equal steps, the loudness of the sound will increase in steps which are perceived as successively smaller. A decibel doesn’t really represent a unit of measure like a yard or meter, but instead a pressure value in decibels expresses a ratio between the measured pressure and a reference pressure. On the decibel scale, everything refers to power, which is amplitude squared. And just to confuse things, the reference pressure in air differs from that in water. Therefore a 150 dB sound in water is not the same as a 150 dB sound in air. So when you are describing sound waves and how they behave it is very important to know whether you are describing sound in the sea or in air.

Note on Acoustic Noise Level Units: Hydrophones measure sound pressure, normally expressed in units of micropascals (µPa). Early acousticians working with sound in air, realized that human ears perceive differences in sound on a logarithmic scale, so the convention of using a relative logarithmic scale (dB) was adopted. In order to be useful, the sound levels need to be referenced to some standard pressure at a standard distance. The reference level used in air (20µPa @ 1m) was selected to match human hearing sensitivity. A different reference level is used for underwater sound (1µPa @ 1m). Because of these differences in reference standards, noise levels cited in air do NOT equal underwater levels. To compare noise levels in water to noise levels in air, one must subtract 26 dB from the noise level referenced in water. For example, a supertanker radiating noise at 190 dB (re 1µPa @ 1m) has an equivalent noise level in air of about 128 dB (re 20µPa @ 1m). These numbers are approximate, and amplitude often varies with frequency.

Faster than the Speed of Sound...

The speed of a wave is the rate at which vibrations move through the medium. Sound moves at a faster speed in water (1500 meters/sec) than in air (about 340 meters/sec) because the mechanical properties of water differ from air. Temperature also affects the speed of sound (e.g. sound travels faster in warm water than in cold water) and is very influential in some parts of the ocean. Remember that wavelength and frequency are related because the lower the frequency the longer the wavelength. More specifically, the wavelength of a sound equals the speed of sound in either air or water divided by the frequency of the wave. Therefore, a 20 Hz sound wave is 75 m long in the water (1500/20 = 75) whereas a 20 Hz sound wave in air is only 17 m long (340/20 = 17) in air.

As we descend below the surface of the sea, the speed of sound decreases with decreasing temperature. At the bottom of the thermocline, the speed of sound reaches its minimum; this is also the axis of the sound channel. Below the thermocline the temperature remains constant, but pressure increases which causes the speed of sound to increase again. Sound waves bend, or refract, towards the area of minimum sound speed. Therefore, a sound wave traveling in the sound channel bends up and down and up and down and can travel thousands of meters. Click image for larger view.

The SOFAR Channel

Sound in the sea can often be “trapped” and effectively carried very long distances by the “deep sound channel ” that exists in the ocean. This SOFAR or SOund Fixing And Ranging channel is so named because it was discovered that there was a "channel" in the deep ocean within which the acoustic energy from a small explosive charge (deployed in the water by a downed aviator) could travel over long distances. An array of hydrophones could be used to roughly locate the source of the charge thereby allowing rescue of downed pilots far out to sea. Sound, and especially low-frequency sound, can travel thousands of meters with very little loss of signal. Read more information on the SOFAR channel.

The field of ocean acoustics provides scientists with the tools needed to quantitatively describe sound in the sea. By measuring the frequency, amplitude, location and seasonality of sounds in the sea, a great deal can be learned about our oceanic environment and its inhabitants. Hydroacoustic monitoring (listening to underwater sounds) has allowed scientists to measure global warming, listen to earthquakes and the movement of magma through the sea floor during major volcanic eruptions, and to record low-frequency calls of large whales the world over. As our oceans become more noisy each year, the field of ocean acoustics will grow and only become more essential. For more information and a tutorial on ocean acoustics .

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Understanding Sound in the Ocean

Levels of underwater noise from human activities—including from ships, sonar, and drilling—have increased dramatically. Those growing levels of ocean noise affect marine animals and habitats in complex ways.

What is sound?

Photo: Sensing with sound: Light doesn't travel well through ocean water: over half the light falling on the sea surface is absorbed within the first meter of water; 100m down and only 1 percent of the surface light remains. That's largely why mighty creatures of the deep rely on sound for communication and navigation. Whales, famously, "talk" to one another across entire ocean basins, while dolphins use sound, like bats, for echolocation. Photo by Bill Thompson courtesy of US Fish and Wildlife Service .

Robert Boyle's classic experiment

Artwork: Robert Boyle's famous experiment with an alarm clock.

How sound travels

Artwork: Sound waves and ocean waves compared. Top: Sound waves are longitudinal waves: the air moves back and forth along the same line as the wave travels, making alternate patterns of compressions and rarefactions. Bottom: Ocean waves are transverse waves: the water moves back and forth at right angles to the line in which the wave travels.

The science of sound waves

Picture: Reflected sound is extremely useful for "seeing" underwater where light doesn't really travel—that's the basic idea behind sonar. Here's a side-scan sonar (reflected sound) image of a World War II boat wrecked on the seabed. Photo courtesy of U.S. National Oceanographic and Atmospheric Administration, US Navy, and Wikimedia Commons .

Whispering galleries and amphitheaters

Photos by Carol M. Highsmith: 1) The Capitol in Washington, DC has a whispering gallery inside its dome. Photo credit: The George F. Landegger Collection of District of Columbia Photographs in Carol M. Highsmith's America, Library of Congress , Prints and Photographs Division. 2) It's easy to hear people talking in the curved memorial amphitheater building at Arlington National Cemetery, Arlington, Virginia. Photo credit: Photographs in the Carol M. Highsmith Archive, Library of Congress , Prints and Photographs Division.

Measuring waves

Understanding amplitude and frequency, why instruments sound different, the speed of sound.

Photo: Breaking through the sound barrier creates a sonic boom. The mist you can see, which is called a condensation cloud, isn't necessarily caused by an aircraft flying supersonic: it can occur at lower speeds too. It happens because moist air condenses due to the shock waves created by the plane. You might expect the plane to compress the air as it slices through. But the shock waves it generates alternately expand and contract the air, producing both compressions and rarefactions. The rarefactions cause very low pressure and it's these that make moisture in the air condense, producing the cloud you see here. Photo by John Gay courtesy of US Navy and Wikimedia Commons .

Why does sound go faster in some things than in others?

Chart: Generally, sound travels faster in solids (right) than in liquids (middle) or gases (left)... but there are exceptions!

How to measure the speed of sound

Sound in practice, if you liked this article..., find out more, on this website.

• Electric guitars
• Speech synthesis
• Synthesizers

On other sites

• Explore Sound : A comprehensive educational site from the Acoustical Society of America, with activities for students of all ages.
• Sound Waves : A great collection of interactive science lessons from the University of Salford, which explains what sound waves are and the different ways in which they behave.

Educational books for younger readers

• Sound (Science in a Flash) by Georgia Amson-Bradshaw. Franklin Watts/Hachette, 2020. Simple facts, experiments, and quizzes fill this book; the visually exciting design will appeal to reluctant readers. Also for ages 7–9.
• Sound by Angela Royston. Raintree, 2017. A basic introduction to sound and musical sounds, including simple activities. Ages 7–9.
• Experimenting with Sound Science Projects by Robert Gardner. Enslow Publishers, 2013. A comprehensive 120-page introduction, running through the science of sound in some detail, with plenty of hands-on projects and activities (including welcome coverage of how to run controlled experiments using the scientific method). Ages 9–12.
• Cool Science: Experiments with Sound and Hearing by Chris Woodford. Gareth Stevens Inc, 2010. One of my own books, this is a short introduction to sound through practical activities, for ages 9–12.
• Adventures in Sound with Max Axiom, Super Scientist by Emily Sohn. Capstone, 2007. The original, graphic novel (comic book) format should appeal to reluctant readers. Ages 8–10.

Popular science

• The Sound Book: The Science of the Sonic Wonders of the World by Trevor Cox. W. W. Norton, 2014. An entertaining tour through everyday sound science.

Academic books

• Master Handbook of Acoustics by F. Alton Everest and Ken Pohlmann. McGraw-Hill Education, 2015. A comprehensive reference for undergraduates and sound-design professionals.
• The Science of Sound by Thomas D. Rossing, Paul A. Wheeler, and F. Richard Moore. Pearson, 2013. One of the most popular general undergraduate texts.

Text copyright © Chris Woodford 2009, 2021. All rights reserved. Full copyright notice and terms of use .

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Sound is a form of energy transmitted through pressure waves; longitudinal or compressional waves similar to the seismic P-waves we discussed in section 3.3 . With ocean sounds, the energy is transmitted via water molecules vibrating back and forth parallel to the direction of the sound wave, and passing on the energy to adjacent molecules. Therefore, sound travels faster and more efficiently when the molecules are closer together and are better able to transfer their energy to neighboring particles. In other words, sound travels faster through denser materials. Since water is much denser than air, the speed of sound in water (about 1500 m/s) is approximately five times faster than the speed in air (around 330 m/s). This helps explain why we sometimes have difficulty localizing the source of a sound that we hear underwater. We localize sound sources when our brains detect the tiny differences in the time of arrival of sounds reaching our ears. A sound coming from our left will reach our left ear a fraction of a second before reaching our right ear. Our brains can process that small difference in time of arrival to recognize the direction from which the sound came. In water, the sound is so much faster that the difference in arrival time between our ears becomes too small for us to interpret, and we lose the ability to localize the source.

However, as with sound in air, the speed of sound in the ocean is not constant; it is influenced by a number of variables including temperature, salinity , and pressure, and an increase in any of these factors will lead to an increase in the speed of sound. We have seen that these variables change with depth and location; so to will the speed of sound differ in different regions of the ocean.

To examine the way the speed of sound changes as a function of depth, we need to consider the vertical profiles for temperature and pressure. At the surface, the pressure is low, but the temperature is at its highest point in the water column. The temperature effects dominate at the surface, so the speed of sound is fast in surface waters. As depth increases, the temperature and the speed of sound decline. Near the bottom, the extreme pressure dominates, and even though temperatures are low, the speed of sound increases with depth. At moderate depths (between a few hundred and one thousand meters) there is a zone where both temperature and pressure are relatively low, so the speed of sound is at a minimum. This zone of minimum speed is called the SOFAR channel ( So und F ixing A nd R anging) or the Deep Sound Channel (Figure 6.4.1).

The SOFAR channel is important because sounds produced in that region can be propagated over very long distances with little attenuation (loss of energy). Sound waves produced in the channel radiate out in all directions. Waves that travel into shallower or deeper water outside of the sound channel are entering a region of faster sound transmission. As we saw with seismic waves, when these sound waves encounter a region of differing transmission speed, the waves tend to be refracted or bent back towards the region of lower speed. As a result, sound waves moving from the SOFAR channel into shallower water will be refracted back towards the channel. As the sound waves go deeper below the channel, they will be refracted upwards, back into the channel and the region of slower speed. In this way, much of the sound does not dissipate out into the water in all directions, but instead is trapped within the channel, and can travel very long distances with little loss of energy (Figure 6.4.2).

There are several practical applications of the SOFAR channel. Baleen whales are thought to use the SOFAR channel to communicate with each other over long distances of hundreds to thousands of kilometers. Their vocalizations are very loud and are low frequency calls, which travel farther than high frequency sounds in the oceans. The military has been able to track submarines using the SOFAR channel, and during World War II it was used to locate downed pilots or missing ships and planes. A stranded pilot could drop a small device into the water, and once it sank into the SOFAR channel it would explode, creating a sound that could be heard at multiple listening stations. Using the time of arrival of the sound at the various receivers, the location of the source could be determined through triangulation. In the 1990s it was suggested that the SOFAR channel could be used to monitor global ocean temperatures. A project known as ATOC (Acoustic Thermometry of Ocean Climate) was proposed where loud, low frequency sounds produced near Hawaii and California would travel through the SOFAR channel to receiving stations around the Pacific. By monitoring the time it took for the sounds to reach the receivers, scientists could monitor changes in ocean temperatures on a global scale, as sounds would move faster through a warming ocean.

Since sound travels better through water than air, the energy required to transmit a given sound wave is higher in air than in water. The energy, or intensity (loudness) of a sound is measured on the decibel (dB) scale. It turns out that it takes about 61 times more energy to transmit a sound through air than through water. Because of this energy difference, there is a 61 dB difference between sounds transmitted through air and water, such that a sound intensity of 120 dB in water would be equivalent to an intensity of about 60 dB in air. This should be kept in mind when trying to compare sounds in the ocean with sounds in the air. A sound of 130 dB in air is about equivalent to standing 100 m from a jet engine at takeoff. A sound of 130 dB in water is equivalent to about 70 dB in air, which is the intensity of the sound of a vacuum cleaner. It should also be pointed out that on the dB scale, an increase of 10 dB means the sound is 10 times louder. In other words, 20 dB is 10 x louder than 10 dB, while 30 dB is 100 x louder than 10 dB.

• Discovery of Sound in the Sea website: http://www.dosits.org/

a seismic body wave that is characterized by deformation of the rock in the same direction that the wave is propagating (compressional vibration) (3.3)

mass per unit volume of a substance (e.g., g/cubic cm) (6.3)

the concentration of dissolved ions in water (5.3)

range of depths around 1000 m where sound travels the slowest, so sound waves are refracted back into the channel and can be propagated long distances (6.4)

Introduction to Oceanography Copyright © by Paul Webb is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Marine animals, including humpback whales, use underwater sound to communicate, navigate, find food and mates, and avoid predators. (Image credit: NOAA National Marine Sanctuary Program)

Soundcheck: Ocean noise

What is ocean noise, animals make noise and hear ours too, waterways getting busier, noisier, finding solutions.

The ocean has always been a noisy place. Many natural sources—like storms, earthquakes, and animals—create underwater sounds. But with the rise of the industrial age, levels of underwater noise from human activities—including from ships, sonar, and drilling—increased dramatically.

Not all sound is created equal. Sources of ocean noise vary in many ways, including how loud they are (intensity, measured in decibels), how long they last (fractions of a second to never ending), and their pitch or tone (frequency, measured in hertz). Think about frequencies relative to tones on a piano. Way down low on the bottom keys are the frequencies that most of the large whale species, as well as large numbers of fish species, use to communicate.

Those growing levels of ocean noise affect marine animals and habitats in complex ways. For one thing, sounds below the surface differ from noises you hear above the waves. Underwater, noises travel farther. In one experiment from the early 1990s, researchers placed a speaker near Antarctica, played some low-frequency or deep-pitched sounds, and picked up those sounds near Bermuda—demonstrating that sound can literally travel halfway around the world.

NOAA has a responsibility to protect marine species and their habitat, which is why we’re working with scientists around the world to further our understanding on ocean noise. Our data and information ultimately help government agencies and industries reduce effects on our ocean resources.

Noise comes in many flavors—ranging from short-term, loud bursts with potentially acute impacts, to long-term, lower level chronic degradation of the background noise environment. NOAA has a role in trying to understand and manage the effects from each.

Marine animals use underwater sound in many important ways. Just as people talk to each other, marine animals use sound to communicate. However, also like people, vocal marine species hear much more than the sounds they use to communicate with one another. Marine species use their hearing to find food and mates, avoid predators, and navigate. Sound is critical to the survival of a great many marine species.

These animals have had 40 to 50 million years or more to evolve in their acoustic environment. But with the advent of the industrial age, people have drastically altered the underwater soundscape over the course of roughly a century. And sometimes how people use the marine environment can affect daily life and functions of marine species.

For this reason, NOAA works with other federal agencies and industries, who are proposing projects that might affect marine species and their habitat—such as oil and gas exploration and drilling, construction, or military training activities—that create loud underwater sounds over specified periods of time. If those sounds could negatively affect marine animals or their habitat, NOAA can require measures and can recommend best practices to reduce negative effects. For example, some measures can avoid noisy activities in specific places when they are important to protected animals or are important to fishery species. Other measures seek to reduce noise exposure for sensitive ecosystems within areas of designated national significance, like National Marine Sanctuaries.

Global forecasts continue to suggest large increases in both the size and number of ships, which predict more noise to come.

Commercial shipping growth has greatly altered the soundscape. In some places, like off Central California, scientists see a strong relationship between growth in large commercial shipping fleets and measurements of lower frequency noise. They are the same frequencies used in the songs of male fin whales and blue whales and by spawning fish such as cod and haddock.

Because shipping traffic is such a major contributor to chronic noise, in 2014 the United States (with NOAA and the U.S. Coast Guard at the helm) led a group within the International Maritime Organization in ratifying voluntary guidelines on ways that ships can reduce noise. NOAA will continue to work with partners, including those within the shipping industry, to incentivize building new and retrofitting existing ships to be quieter.

We’re finding win-win solutions to some of our problems. For example, propellers can create bubbles underwater that burst with a signature sound. In addition to noise, those bubbles are thought to create fuel inefficiency. One question is whether a quieter propeller that produces less noise would also be more efficient to make up the difference in upfront cost. Because large shipping companies face pressure to comply with stricter carbon emission standards, propeller changes in tomorrow’s ships could help both shipping operators and the environment.

The United States is not alone in these efforts. Ports in British Columbia, Canada, are creating incentives for shipping companies to figure out how much noise they make compared to other ships and reward those with good environmental status.

NOAA is working with partners around the world to develop new tools to better understand the complexities of ocean noise and is developing strategies that help governments and industries address it.

Given NOAA’s mission to keep marine resources sustainable and resilient for future generations, we recognized the need to tackle the issue of man-made ocean noise in a holistic way. In 2010, NOAA committed to improve tools that the agency uses to assess the effects of man-made sound on whales, dolphins, and porpoises.

Current number of underwater reference stations in U.S. waters tracking ocean noise levels over time for the federal government. 

This led to two complementary efforts —one to produce maps of where these animals are located and in what densities within U.S. waters, and another to predict levels of underwater noise from human activities . Scientists can use these maps, along with other information, to better understand what is happening underwater and where higher levels of human-produced noise overlap with the marine mammals. With these maps complete, NOAA began to push forward on a long-term visionary plan regarding ocean noise effects.

In the fall of 2016, NOAA released our final Ocean Noise Strategy Roadmap . The strategy is a NOAA initiative that seeks to guide the agency toward more comprehensive and effective management of the effects of man-made ocean noise over the next decade. The Strategy includes steps to improve what we know about underwater noise, and how we can work to minimize adverse effects of ocean noise on marine species and habitats.

One basic thing we still need to learn more about is how noisy it is in different ocean soundscapes and how those levels are changing through time. This research is ongoing. In the meantime, we’re working with partners on new and innovative techniques to further reduce risk while noisy activities are happening, such as placing observers in the area to stop activities when marine mammals come within a certain distance. And in some cases, measures can be taken to make the activity itself quieter, through the application of quieting designs. Examples include using bubble curtains around a pile or using alternative quieter technologies instead of airguns.

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How Does Water Affect Sound?

What Are Areas of Compression & Rarefaction in Waves?

Water affects sound waves in several ways. For example, they move several times faster through water than air, and travel longer distances. However, because the human ear evolved to hear in air, water tends to muffle sounds that are otherwise clear in air. Water can also "bend" sound, sending it on a zigzag path instead of a straight line.

Sound Waves and Water

Sound travels in the form of waves resulting from vibrations emanating from objects. If, by chance, an object is struck or moves, it creates a vibration. These disturbances also cause the surrounding molecules of a medium -- air, liquid or solid -- to vibrate. In turn, the ears receive the tremors of these different substances, which send signals to the brain. These are interpreted as “sounds.”

The production of sound is also the same underwater. When you strike an object, vibrations from the underwater object start to bump surrounding water molecules. The submerged human ear does not hear the sound as easily as above ground. It requires a high frequency or a really loud volume for the human ear to hear it.

Speed of Sound

The speed of sound waves depends on the medium used, not on the number of vibrations. Sound travels faster in solids and liquids, and slower in gases. The speed of sound in pure water is 1,498 meters per second, compared to 343 meters per second in air at room temperature and pressure. The compact molecular arrangement of solids and the closer arrangement of molecules in liquids make these molecules respond more quickly to the disturbances of neighboring molecules than in gases.

Temperature and Pressure

As in gases, the speed of sound underwater is also dependent on density and temperature. In gases, the velocity of molecules increase whenever temperature increases; like gases, sound waves travel faster as temperature increases. Unlike gases, water has a greater density because of its molecular arrangement. Thus, sound waves travel faster underwater as the wave bumps through -- and vibrates with more molecules.

Sound Refraction

Refraction is a complex phenomenon, involving the bending of sound waves as they speed up and slow down when traveling through different mediums. This goes unnoticed in everyday life, yet scientists consider this property important in underwater oceanic study. The speed of sound in the ocean varies. As the ocean gets deeper, the temperature decreases while pressure increases. Sound travels faster at lower depths than at surface level, no matter how sizable the difference in temperature, due to pressure differences. The change in speed changes the direction of the waves, making it hard to determine where the sound originally came from.

Sound and Salinity

Salinity can also be a factor in determining the behavior of sound. In seawater, sound travels up to 33 meters per second faster than in freshwater. Salinity affects sound speed at the surface, especially at river mouths or estuaries. Sound travels faster in the ocean because there are more molecules -- specifically salt molecules -- for waves to interact with, as well as higher surface temperatures.

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About the Author

Steve Johnson is an avid and passionate writer with more than five years of experience. He's written for several industries, including health, dating and Internet marketing, as well as for various websites. He holds a bachelor's degree from the University of Texas.

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How does sound travel in shallow water?

Illustration of a side view of the continental shelf. Image public domain.

In the field of ocean acoustics, “shallow water” commonly refers to coastal waters extending from the shoreline out to the edge of the continental shelf to a depth of about 200 m, where the seafloor slope increases. By this definition, shallow water accounts for approximately 8% of the ocean and seas. These regions are important because they are close to human populations and account for much of the exclusive economic zones (EEZs) of coastal nations. These regions are important for marine habitats, fisheries, national security, commerce, energy development, and recreation.

The following sections include information on the structure of the shallow water sound channel by season (including the sea surface and seafloor), how sound travels in shallow water, and how the shallow water sound channel varies in different parts of the ocean.

The shallow water sound channel

Sound travel in shallow water, geographic variability of the shallow water sound channel.

Speed of sound in water profile when the speed of sound is constant. Credit DOSITS.

The speed at which sound travels in the ocean is faster with increasing temperature , salinity , and pressure (See How fast does sound travel? ). Shallow waters are often well mixed by wind and waves in the winter, with temperature and salinity largely independent of depth. As a result, sound speed is also often largely independent of depth. This is very different from deep water, where there is a minimum in sound speed at a depth of about 1000 m in mid-latitudes, forming a sound channel or waveguide through which sound can propagate over long distances without interacting with the sea surface or seafloor (See How does sound travel long distances? The SOFAR Channel ). In shallow water, sound travels on paths that interact with the seafloor and ocean waves at the sea surface.

Sound speed is largely independent of depth in shallow water in winter. This is particularly true in the mid-latitudes (for more information, see below on geographic variability). When sound speed is constant, sound travels in straight lines. Sound that travels upward from a source travels in a straight line until it hits the surface. Upon reaching the sea surface, the sound is reflected and travels back downward toward the seafloor (See How does sound move? Reflection ). Almost no sound travels into the air. Sound that travels down from a source propagates in a straight line until it hits the seafloor. Upon reaching the seafloor, some of the sound is reflected and travels back upward. Not all of the sound is reflected, however. Some of the sound travels into the seafloor.

The following figure has two parts. On the left is a plot of sound speed as a function of depth. Sound speed is the same at all depths. On the right are the paths followed by sound waves as they travel away from the source. These waves travel in straight lines until they are reflected at the sea surface or the sea floor.

Left: Constant speed of sound through the water column. Right: Paths followed by sound waves as they travel away from the source in shallow water at a constant sound speed. Credit DOSITS.

Vertical distances in this figure are greatly exaggerated compared to horizontal distances. This causes the angles from the horizontal at which sound waves travel to look much steeper than they really are.

Sound loses energy when it hits the ocean surface or seafloor. Whenever sound reflects from the rough ocean surface, some sound energy is scattered and lost. Similarly, whenever sound hits the rough seafloor, some sound energy is scattered and lost. In addition, some sound energy can travel into the seafloor and be attenuated . Absorption in the seabed is much greater than absorption in seawater [for more about absorption see Sound Absorption ].

Whether or not sound goes into the seafloor depends upon the angle to the horizontal at which the sound is traveling. When the sound speed in seafloor is greater than the sound speed in the water above it, which is usually the case, there is a special angle, called the critical angle . The critical angle is usually about 15º. When sound travels at angles to the horizontal that are smaller than the critical angle, the sound is almost perfectly reflected (shown in the blue line in the figure below). When sound travels at angles to the horizontal greater than the critical angle (shown in the yellow line in the figure below), some of the sound enters the seafloor. Sound that travels at angles greater than the critical angle disappears into the seafloor after a few reflections . This is the major source of energy loss in shallow water. Uncertainties in the properties of the seafloor, including sound speed, density , and attenuation , make it difficult to accurately predict how sound travels in shallow water.

An illustration of the reflection and refraction of sound waves when they encounter the seafloor at the critical angle and greater and less-than the critical angle. Credit DOSITS.

Sound waves traveling in the sound channel follow many different paths. Although sound travels away from a sound source in all directions, only sound traveling away from a source on paths that leave the source at specific angles will reach a receiver at a specific location.

Left: Constant speed of sound through the water column. Right: Illustration of the paths between a mid-depth source and a mid-depth receiver at a constant sound speed. Only the sound waves reaching the receive are shown. Credit DOSITS.

The sound waves traveling on different paths from source to receiver have slightly different travel times. A single impulsive source will therefore be heard as a number of separate arrivals. The sound that travels directly from the source to the receiver travels the shortest path and arrives first. Sounds that reflect from the sea surface or seafloor travel further and arrive later. This is different from sound propagation in deep water where the shortest path on the sound channel axis arrives last (See Sound Travel in SOFAR Chanel for more information).

The way in which sound speed changes with depth is not the same everywhere in shallow water because the ocean temperature and salinity profiles that determine sound speed can differ greatly from one location to another and from one time to another. The variability is much higher in coastal regions than in the deep ocean.

Sound speed is independent of depth in shallow water when wind and waves are strong, resulting in fully mixed conditions. This most often occurs in wintertime near the coast in water that is less than roughly 30 m deep. In summertime and in deeper waters further from the coast, the sun warms the water near the surface, but the warming does not extend all the way to the seafloor. Sound speed is higher in the warmer water near the surface than in the colder water near the seafloor. There are often three layers, with a mixed layer near the surface with relatively high sound speed, a layer in which temperature and sound speed decrease, and a cold layer above the seafloor with lower sound speed.

Left: Illustration of ray paths for a source located below the thermocline, showing the rays being refracted toward the seafloor when there is a summer thermocline. Right: Speed of sound through the water column when the speed is not constant. Credit DOSITS.

A sound wave traveling through the ocean is  refracted  (bent) whenever it encounters changes in the speed of sound (See How does sound move? Refraction ). Sound waves are continually refracted toward the region of lower sound speed. Differing sound-speed profiles therefore cause sound waves to travel on quite different paths. For a three-layer profile , sound that travels upward from a source located in the cold water near the seafloor is bent back towards the seafloor when it travels up into warmer water with higher sound speeds. The result is that the sound interacts repeatedly with the seafloor and rapidly becomes weaker.

In shallow water, sound speed often varies as a function of geographic location as well as depth. For instance, on the continental shelf off the east coast of the U.S., the water’s temperature and salinity are influenced by the Gulf Stream and associated eddies. These oceanographic features can form fronts between the colder shelf waters and warmer Gulf Stream current flow. Therefore, the sound speed profiles can be complicated, changing in time and space and resulting in complex acoustic propagation.

Graph of the sound speed on the shelf off the New Jersey shore. Image from Kristy A. Moore, James H. Miller, Gopu R. Potty, James F. Lynch and Arthur Newhall, “Investigation of three‐dimensional propagation effects at the New Jersey shelf break front,” Journal of the Acoustical Society of America 2007 121:5, 3126-3126.

Additional links on DOSITS

• Science of Sound > Sound Movement >  How fast does sound travel?
• Science of Sound > How does sound travel long distances? The SOFAR Channel
• Sound of Sound > Sound Movement > Reflection
• Sound of Sound > Sound Movement > Refraction
• Sound of Sound > Sound Movement > Absorption
• Sound of Sound > Sound Movement > Scattering
• Moore, K. A., Miller, J. H., Potty, G. R., Lynch, J. F., & Newhall, A. (2007). Investigation of three‐dimensional propagation effects at the New Jersey shelf break front . The Journal of the Acoustical Society of America , 121 (5), 3126–3126. https://doi.org/10.1121/1.4808487

How Far Does Sound Travel: The Science of Acoustics

Do you ever stop to think about how sound travels? It’s an interesting phenomenon that occurs everyday and yet we often take it for granted. In this blog post, we will explore the science of acoustics and how sound travels. We will answer the question of how far sound can travel and how it is affected by different factors. Stay tuned for an in-depth look at this fascinating topic!

Nature Of Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through some medium, such as air or water. Sound can propagate through solids and liquids better than gases because the density and stiffness are greater. So how far does sound travel? In this article we will answer how sound travels and how to calculate how far it travels in different scenarios.

Sound Transmits Conception

A common misconception with regard to how sound transmits itself between two points (for example from speaker to ear) is that the source creates waves of compression in the surrounding gas which then proceed on their way at a constant speed until they strike something else; either another solid object or our ears . This analogy might be okay for describing what goes on at low frequencies but once we go beyond around 1000 Hz, the propagation of sound becomes far more complex.

At low frequencies (below around 1000 Hz), sound waves tend to travel in all directions more or less equally and bounce off objects like a rubber ball would. As frequency increases however, the directivity of sound increases as well. So high-frequency sounds are more likely to travel in a straight line between two points than low frequencies. This is why we can often hear someone calling from some distance away when there is loud music playing – because the higher frequencies carry further than the lower ones.

How Far Can Sound Travel

There are three ways that sound can be transmitted: through air, through water, or through solids. The speed of sound through each medium is different and depends on the density and stiffness of the material.

The speed of sound through air is about 343 m/s (or 760 mph), and it travels faster in warmer air than colder air. The speed of sound through water is about 1500 m/s, and it travels faster in salt water than fresh water. The speed of sound through solids is much faster than through either gases or liquids – about 5000-15000 m/s. This is why we can often hear someone coming before we see them – the sound waves are travelling through the solid ground to our ears!

Now that we know how sound propagates and how its speed depends on the medium, let’s take a look at how to calculate how far it will travel between two points. We can use the equation

distance = speed x time

For example, if we want to know how far a sound will travel in one second, we have:

distance = 343 m/s x 0.001 s = 343 m

So sound travels 1 kilometer in roughly 3 seconds and 1 mile in roughly 5 seconds.

Does Вecibel Level affect the Sound Distance?

The surface area around a sound source’s location grows with the square of the distance from the source. This implies that the same amount of sound energy is dispersed over a larger surface, and that the energy intensity decreases as the square of the distance from the source (Inverse Square Law).

Experts of Acoustical control says, that

For every doubling of distance, the sound level reduces by 6  decibels  (dB), (e.g. moving from 10 to 20 metres away from a sound source). But the next 6dB reduction means moving from 20 to 40 metres, then from 40 to 80 metres for a further 6dB reduction.

How Far Can Sound Travel In Real World

In real world, there are many factors that can affect how far a sound travels. Factors such as air density, temperature and humidity have an impact on its propagation; obstacles like buildings or mountains could also block some frequencies from going through while letting others pass (this happens because at high frequencies they behave more like waves).

Sounds can propagate through solids better than they can propagate through air because their density/stiffness are greater (this means that sound travels faster). In addition to this, we also know that it takes less time for a high frequency wave to reach us from its source compared with low frequencies. For example if there’s some kind of obstacle blocking our path then it might take longer for waves at higher frequencies than those below 1000 Hz to past them.

Can Sound Waves Travel Infinitely?

No. The higher the frequency of a sound wave, the shorter its wavelength becomes. As wavelength decreases, the amount of energy in a sound wave also decreases and eventually it dissipates completely. This is why we often can’t hear someone calling from very far away when there’s loud music playing – because the high frequencies are being blocked out by all the noise!

Can Sound Travel 20 Miles?

The air may be permeable to these lower-frequency, sub-audible sound waves generated by elephants. Some whale species’ frequencies might travel through seawater for 1500 kilometers or 900 miles.

How Far Can a Human Scream Travel?

The normal intelligible outdoor range of the male human voice in still air is 180 m (590 ft 6.6 in).

The Guiness World Record of the Farthest distance travelled by a human voice belongs the Spanish-speaking inhabitants of the Canary Island of La Gomera, is intelligible under ideal conditions at 8 km (5 miles).

In Conclusion

At the end of this blog post, you should have a better understanding of how sound travel and what factors affect it. If you want to learn more about acoustics and sounds, you can check out our resources here.

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Sound is a pressure wave, but this wave behaves slightly differently through air as compared to water. Water is denser than air, so it takes more energy to generate a wave, but once a wave has started, it will travel faster than it would do in air.

A relay race

Sound travels by particles bumping into each other as they vibrate. It is a little like a relay race – each runner holds a little bit of information (the baton), and when they make contact with the next runner, they pass the information on.

In the case of sound, the runners are particles and the information (baton) they are passing along is energy of vibration. In a sound wave, a particle picks up some energy and keeps it until it bumps into a neighbouring particle. The next particle will then pick up the energy and transfer it to the next one in the chain. This happens extremely fast and is detected as a wave of pressure.

Sound won’t travel in a vacuum because there are no particles to bump together to transmit the vibration.

Sound in air

In a gas like air, the particles are generally far apart so they travel further before they bump into one another. There is not much resistance to movement so it doesn’t take much to start a wave, but it won’t travel as fast.

Sound in water

In water, the particles are much closer together, and they can quickly transmit vibration energy from one particle to the next. This means that the sound wave travels over four times faster than it would in air, but it takes a lot of energy to start the vibration. A faint sound in air wouldn’t be transmitted in water as the wave wouldn’t have enough energy to force the water particles to move.

Sound in solids

In a solid, the particles are even closer together and linked by chemical bonds so the wave travels even faster than it does in either liquid or air, but you need quite a lot of energy to start the wave at the beginning.

Sound and temperature

Temperature has a marked influence on the speed of sound. This is not due to a change in how closely together the particles are to each other but relates to the amount of energy that each particle has. Hot particles have more energy and transmit sound better than cold particles. Water in Antarctica will transmit sound slower than water in the tropics.

Some comparisons for the speed of sound in different materials

Related content.

Explore the science concept related to sound further with these articles:

• Hearing sound – the basics of sound waves
• Measuring sound – the different parts of a sound wave, how we talk about and measure sound
• Sound – visualising sound waves – helps students to 'see’ sound waves with videos and diagrams

In our recorded PLD session Sounds of Aotearoa a group of primary science educators introduce some fun ways you can learn and teach about sound.

Activity ideas

Use these activities to explore some essential physics ideas relating to sound, but in a whole new way.

• Modelling waves with slinkies – stay indoors and model how sound travels.
• Catching worms using ground sounds – go outdoors and investigate whether there is any evidence that earthworms respond to vibrations in the ground.
• Sound detectives – can you locate sounds while blindfolded?
• Make and use a hydrophone – and listen to underwater sounds.
• Sound on an oscilloscope – use oscilloscope software and your computer to make and watch a visual sound display.
• Investigating sound – simple exploratory activities and questions to experience and build an understanding of sound.
• Hearing sounds – using whispers and vibrations to hear and experience how sound moves.
• Hearing sounds under water – go underwater yourselves to listen to sounds
• Measuring the speed of sound – use a timing app to measure the speed of sound.

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Does Sound Travel Faster in Water or Air?

Most people, whether they are students or workers, have a pretty clear idea of how sound works. After all, who hasn’t heard about sound waves, vibrations, and other similar concepts? Yet, there are a few notions that still baffle people to this day, particularly regarding the way sound propagates in water and air. And, with so much contradictory information online, it’s easy to see why.

So, if you’re one of the many who want to know if sound travels faster in water or air, this article has got you covered. But first, let’s start with the basics!

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What Is Sound?

Generally speaking, sound is a type of longitudinal mechanical wave that travels through a medium. However, there are two definitions regarding how sound is produced.

For starters, in physiology, sound is created when an object’s vibrations travel through a medium until they reach the human eardrum . In physics, sound is produced in the form of a pressure wave . More specifically, when objects vibrate, they cause the nearby molecules to also vibrate, triggering a chain reaction of sound wave vibrations in the specific medium.

But no matter which definition you prefer, you’ll notice a similarity — sound needs a medium to propagate and will not travel through a vacuum. As a matter of fact, sound travels at different speeds depending on the medium. In other words, the medium’s density and compressibility directly affect the speed of sound. For instance, sound waves will travel slower in a less dense and more compressible medium .

How Fast Does Sound Travel in Water?

When it comes to water, sound can travel as fast as 1,498 meters per second, or approximately 3,350 miles per hour . However, as mentioned earlier, the physical characteristics of the medium highly affect the speed.

As a result of its high salinity, seawater, such as oceans, allows sound to travel up to 33 meters per second faster than the freshwater found in lakes . That’s because salt molecules respond quickly to the disturbances of neighboring molecules, propagating sound waves faster and at longer distances.

The speed of sound is also dependent on density. As you might already know, water has an impressive density due to its unique molecular arrangement. Thus, sound waves can travel much faster underwater as the wave bumps and vibrates with more molecules.

Temperature and Pressure

You need to understand that, as the ocean gets deeper, its temperature decreases and its pressure increases. These affect the particle arrangement and, by extension, the speed of sound. To put it simply, sound travels slower at the surface level than at lower depths.

How Fast Does Sound Travel in Air?

Sound is able to travel through the air at an average of 332 meters per second, or 742 miles per hour. Although that might seem fast, it is not nearly as fast as light , which travels at 186,411.358 miles per hour. But as with water, there are also many factors that affect how sound propagates in the air:

Temperature

Air molecules tend to have more energy at higher temperatures, meaning that they will vibrate faster. That allows sound waves to also travel faster and farther , as they are propelled by molecule collisions. Yet, as the sound moves through the atmosphere, some parts of its wave will travel faster than others due to temperature differences.

What’s interesting about sound is that, at a constant temperature, its speed is not dependent on the pressure of the medium. That’s because these two properties are tied to one another. So, increasing temperature will also increase pressure and, consequently, the speed of sound.

Air Direction

The wind direction can impact the speed of sound and the distance it can travel . In fact, you might notice that sound levels are higher when the wind is blowing down, such as from a highway towards the ground level.

Water vapors are less dense than dry air at a constant temperature. Naturally, the presence of moisture will decrease the air’s density and increase the speed of sound. Therefore, humid environments experience much faster sound propagation than dry and cold areas.

Why Does Sound Travel Faster in Water Than Air?

By now, you might have noticed that sound travels about four times faster in water than in air. The main reason behind this is that water is denser than air. Sure, not all water has identical properties , as salinity and temperature vary and affect its density. But even so, molecules in the water are closer together, causing more vibrations to be transmitted at a faster speed of sound.

Furthermore, water is an incompressible environment . Actually, it’s better to imagine water as being similar to a solid object, as they tend to behave similarly when it comes to compression. More specifically, when water encounters a force, it will immediately transfer its energy to nearby molecules, just like solids. This characteristic is partially offset by the water’s high density, creating the perfect environment for sound to travel through.

And lastly, it’s important to mention that sound travels faster in harder materials . It’s true that water as a unit is not necessarily hard; however, it has a strong bond between its molecules. Hence, the propagation of sound is faster as it passes more quickly from one particle to the next.

But Why Is It Harder to Talk to Someone Underwater?

Naturally, you might assume that, since sound travels faster in water, it would be incredibly easy to chat with someone while swimming or diving . But that couldn’t be further from the truth.

When someone talks, they do so by emitting air and sending compression waves through it. That’s thanks to your lungs, vocal cords, and mouth, which work together to imprint a sound waveform on the burst of air that comes from your body. So, in order for someone that’s in the water to hear you, the sound will need to travel from your mouth into the surrounding water.

However, sound couples very poorly from air to water. As a matter of fact, water tends to reflect external sound waves instead of allowing them to penetrate its surface. That’s also the reason why phenomenons like echos occur when you scream or talk near a well, as the water at its bottom reflects the sound waves back to you.

What About Sound Travel Distance?

When it comes to sound travel, water is again the clear winner, as it allows sound to propagate to distances of almost 15,500 miles. To understand why that’s the case, imagine a whale that is swimming through the ocean and calls out to its peers. The sound waves it produces move similarly to ripples in the water.

As the sound travels and reaches increasing depths , it begins to slow down and eventually refracts downward. Once the sound reaches a region called the thermocline layer, its speed further decreases to a minimum. That’s because the thermocline layer features rapid changes in pressure and temperature.

After breaking through the layer, sound waves encounter another area where the temperature remains constant. However, the pressure continues to rise, which causes a boost in the sound speed, making it refract upward. This channeling of waves allows the sound to travel thousands of miles with little to no energy loss. It’s thanks to this process that scientists can pick up whale songs from many miles away.

Key Takeaways

Understanding how sound works and travels is extremely important. Sure, you might not deal with mediums like water every day. However, air is all around you, and learning the way it affects sound speed can help you figure out the perfect way to soundproof your environment and enjoy a noise-free life!

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• Does Sound Travel Faster Than Light?
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• Best Sound Absorbing Materials
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Next stop: Sound Transit East Line now links Bellevue to Redmond

Despite delays connecting the 2 Line to Seattle, hundreds rode the rails this weekend as the eight stations opened after years of construction.

• Jadenne Radoc Cabahug &

Venice Buhain

People hold up their phones as the first trains arrive to pick up the first passengers at the Bellevue Downtown Station during the opening of Sound Transit’s 2 Line light-rail service in Bellevue on Saturday, April 27, 2024. (Jason Redmond for Cascade PBS)

Sound Transit’s long-anticipated East Link debuted over the weekend, connecting Bellevue with Redmond via light rail.

The train, which will eventually travel across Lake Washington, has been a long time in the works. The extension project, formally approved by voters in 2008, was expected to cost about $3.68 billion for the line. By next year, Sound Transit expects to connect Bellevue to Seattle – where Link Light Rail opened in 2009.

Passengers take in the view of the Bellevue skyline during an innagural ride on Sound Transit’s 2 Line. (Jason Redmond for Cascade PBS)

The current configuration of what’s called the 2 Line is expected to move about 6,000 riders between Bellevue and Redmond daily on trains with two cars each, according to the agency. That number is expected to rise once the connection to Seattle is completed. Currently, Eastside riders can connect between South Bellevue and Downtown Seattle via bus.

More expansions are coming in the next few years. Light rail connecting Shoreline, Mountlake Terrace and Lynnwood to the existing 1 Line in Seattle is scheduled to open in the fall. Two more Eastside stations – Marymoor Village, next to the popular Marymoor Park, and Downtown Redmond – are anticipated to open next year.

Trains arrive at the Bellevue Downtown Station on opening day of Sound Transit’s 2 Line light-rail service in Bellevue on Saturday. (Jason Redmond for Cascade PBS)

The original plan for East Link was for a mid-2023 opening, but construction delays pushed the opening date back one year . Then, plans to open this year all the way from Seattle to Redmond over the Interstate 90 bridge were derailed when the agency announced last year that the rail line’s I-90 supports had to be redone due to faulty concrete . That connection, which will include stations at Judkins Park and Mercer Island, is expected to open in 2025 at the same time as the Redmond stations.

King County Councilmember and Sound Transit board member Claudia Balducci said the agency opted to get use out of the completed stations, and perhaps give people who had never taken light rail the chance to experience it.

“Option 1 was to mothball the stations and pay for security for a year. Option 2 was to open it to the public and get some use out of it,” said Balducci, who pushed for the East Link partial opening.

Sound Transit Interim CEO Goran Sparrman speaks at the opening of Sound Transit’s 2 Line light-rail service. (Jason Redmond for Cascade PBS)

The crowd listens to speakers at the opening of Sound Transit’s 2 Line light-rail service. (Jason Redmond for Cascade PBS)

King County Executive Dow Constantine, second from right, and U.S. Sen. Maria Cantwell applaud remarks at the opening of Sound Transit’s 2 Line. (Jason Redmond for Cascade PBS)

From left, former Sound Transit CEO Joni Earl (seated); Bellevue Mayor Lynne Robinson; U.S. Sen. Maria Cantwell; Microsoft Vice Chair and President Brad Smith; U.S. Sen. Patty Murray; King County Executive Dow Constantine; King County Councilmember Claudia Balducci (holding scissors); Gov. Jay Inslee; Redmond Mayor Angela Birney; and Lynnwood Mayor Christine Frizzell at the ribbon-cutting ceremony for the opening of Sound Transit’s 2 Line light-rail service. (Jason Redmond for Cascade PBS)

Balducci also pointed out that the 1 Line between Tukwila and Seattle originally opened only between Tukwila International Boulevard and Westlake Station, with extensions to the south and north following in the decade afterward.

Balducci, who has been working on the East Link extension since she was a Bellevue City Councilmember in the late 2000s, said she was delighted to see the trains start moving.

“I’ve been working on this for almost two decades. All this work is finally turning into service,” she told Cascade PBS a few days before the official opening of the line.

Redmond Mayor Angela Birney said ever since the locations of the stations were identified, the city has approved multifamily housing and other amenities nearby to capitalize on the transit option.

“We put a lot of housing right around our stations and many of those families … would rather not use their cars. That’s intentionally that they moved to those areas. So I’m really excited for them to actually be able to get on the train and leave their cars behind,” Birney said.

The city also added two bike/pedestrian bridges for the Redmond stations.

“And so we’re really making another option for people to ride, bike, get on the train and get through the Eastside,” Birney said.

Passengers exit as others wait to board Sound Transit’s 2 Line. (Jason Redmond for Cascade PBS)

Hundreds of people attended the ribbon-cutting Saturday at the Downtown Bellevue station, despite the gray skies and cold rain, although many more boarded at other stations just to ride the rails. Royal-blue balloons and booths lined the station adjacent to the Bellevue Transit Center on Northeast Sixth Street near Meydenbauer Center, with local booths lined up as well as food trucks from local businesses.

Redmond resident Gary Fujioka boarded the train with his electric bike at the Redmond Technology Station on opening day and rode it south to celebrate. 

“It’s busier than I thought it would be, but that’s a good thing. I’m surprised by the turnout; I hope all these people return and use it regularly,” Fujioka said. “Everybody should be open-minded to our public transportation in the region and I invite them to come out and try it, it’s much nicer than you think it is.” 

Sound Transit says the trip between Redmond Technology Center near Microsoft and Bellevue Downtown should take about 10 minutes. The trains come by each station every 10 minutes seven days a week, from 5:30 a.m. to 9:30 p.m.

Passengers take in the view from above State Route 520. (Jason Redmond for Cascade PBS)

On Saturday public officials from Bellevue, Redmond and King County were in attendance alongside Gov. Jay Inslee and both U.S. Senators Maria Cantwell and Patty Murray. Representatives from Microsoft and Amazon, which have built up their workforces on the Eastside over the past decades, also attended.

Attendees of all ages – from small children wearing Thomas the Tank Engine train conductor hats to groups of the elderly – came to the Bellevue downtown station to celebrate. Many took photos and videos to commemorate the opening of the line that took two decades to complete. Although it’s not yet connected to other regions around Puget Sound, people traveled from Mercer Island or Seattle and even as far as Vancouver, B.C., to experience the moment. 

People crowded each station entrance to watch the ribbon-cutting and cheered all the way down the tracks as two trains pulled in. Riders were excited as they filled cars, many with no specific destination in mind.

Most riders were taking the train to enjoy the journey, or to stop at each station and look at the artwork, only to hop on the next train and repeat the process across the eight stations.

People explore the Redmond Technology Station. (Jason Redmond for Cascade PBS)

Jenny Pai and her family drove down from Bothell for the event. Her family wanted to take the line for an adventure. Pai said that if more lines open, she’d be open to taking the train to work.

Like Pai, retiree Sand Stron from Mercer Island came for the opening day just to travel south to north and vice versa to his parking spot in the South Bellevue parking garage. 

“I think this is an important thing for our region and we’re looking forward to it coming from Mercer Island. We’ll probably use the transit a lot.” 

University of Washington student Yoshi Takano came with a group of 25 from the university chapter of the Institute of Transportation Engineers, a group passionate about improving transportation in the state. Takano said attendees from the University of Oregon also came for the opening day. The groups were going up and down the line, stopping at each station to explore. 

“There’s been construction delays and I think that’s frustrating, but I’m glad they were able to open this segment. I think they wanted to be able to show voters that their tax dollars are going to something that’s positive and show the benefits of the light rail,” Takano said. 

He hopes that people will continue to use it regularly, but worries that they’ll still opt to drive instead due to the abundance of parking in Bellevue. 

“But that doesn’t necessarily mean it’s a failure, it’s a product of past policies and it’ll require additional new development and as they finish the line to Seattle; I think ridership can increase,” Takano said. 

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About the Authors & Contributors

Jadenne Radoc Cabahug

Jadenne Radoc Cabahug is Crosscut's emerging journalist news fellow for 2024.

Venice Buhain is Cascade PBS' associate news editor. She previously covered education at Crosscut, and also worked for KING 5, The Seattle Globalist and TVW News. You can follow her on Twitter @venicebuhain  or contact her at [email protected] .

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