Did you ever wonder why sound seems to be amplified over water? Sound waves on top of the water seem to be louder than overland. Why does this happen, Does Water Amplify Sound?
- Yes-H2O molecules are held closer together & can quickly transmit energy (sound waves) through vibration making it more than 4x faster than molecules in the air.
- Water temperature causes Refraction a phenomenon that amplifies sound on the surface of the H2O, both dependent on temperature & pressure.
Remember those old World War II movies when the crew in a submarine is nervously waiting for an enemy ship to cross paths with them and extremely quiet in the area because they might be heard? Even the tiniest whispers from the guys on the Sub could be amplified and heard for miles.
Does Water Amplify Sound
Yes. Water affects sound waves in several different ways. They can move several times faster than sound waves move through the air. However, because the human ear evolved over millions of years to hear in the air, water tends to muffle sounds that otherwise would be clear in the air. Water can also “bend” sound, sending it on a zigzag path instead of a straight line.
Sounds travel in the form of waves resulting from vibrations coming from objects. If by chance, any object is struck or moves, it creates a vibration. 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.
Do Sound Waves Travel Through Water
The production of sound is also the same underwater. When you strike an object, it will cause vibrations from the underwater object and start to travel and 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.
The Speed of sound waves depends on the medium used not how many vibrations are created. Sound will travel faster in solids and liquid medium and slower in gases. The speed of sound in pure water is 1,498 meters per second, compared to 343 meters per second in the air at room temperature and pressure.
The compact molecular arrangement of solids and the closer arrangement of molecules in water or liquids make these molecules respond more quickly to the disturbances of neighboring molecules than what would happen above water in gases. That makes sound travel faster underwater.
In the ocean, the sound will travel even faster because the salt contained in the water again holds more molecules in a tighter pattern than in water namely more molecules because of salt. It will travel 33 meters per second faster than freshwater.
As any waveform will decrease over a distance like a pebble in a pond the amplitude or rings made by the pebble will decrease. Just like sound from a source that is created will decrease as their waves move farther spreading out in distance.
There is evidence that water can amplify sound waves as when you are sitting in a boat, a sound coming from the shore will seem louder than the same sound heard by a person on land. The sound seems to be amplified when it travels over water.
The reason is that the water cools the air above its surface, which then slows down the sound waves near the surface. This causes refraction or bending of the sound wave, such that more sound reaches the boat for the person to hear it.
Refraction of the sound waves in cooler air and the reflection off the surface of the water affect the sound that is heard. This is a very common effect and if you have been on a boat and on the water you have experienced this type of amplification of sound waves.
The Speed of Sound Waves in Water
Even though sound waves in water and sound waves in air are somewhat similar, the way that Sound Levels in water and sound levels in the air are reported is different, and comparing sound levels in water and air must be done carefully.
Normally sound levels are measured in DBS. Sound pressures for transient signals are sometimes given as peak or peak-to-peak pressures, rather than mean-square pressure.
When we describe a sound as loud or soft, scientists say that the sound has a high or low amplitude or intensity. Amplitude refers to the change in Pressure- which is the amount of force per unit area measured in units of atmospheres (atm) as the sound wave passes by.
Amplitude is the maximum distance that a vibrating particle moves from its Equilibrium or the rest position of the particles in the medium and how much the Medium is disturbed.
Medium means substance or material that carries or transports the Wave from its source to other locations. In the open ocean, the medium through which the wave travels is ocean water.
The average amount of sound power or (sound energy per unit of time) is transmitted through a unit area in a specified direction. The unit of intensity is watts per square meter.
For simplicity, the magnitude of the intensity is often referred to as the intensity, without specifying the direction in which the sound is traveling.
If you increase the amplitude of a sound, you are making it louder, just as you do when you turn up the volume on your radio. If you decrease the amplitude, you are making the sound softer, just as when you turn down the volume.
Sound In Air- In a gas-like air, the molecules are spread 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. The same vibration in all three mediums would take the least amount of energy to get going.
Sound In Water-In water the molecules are closer together and because of this, they can quickly transmit energy through vibration from one particle to the next.
This equates to more than 4x faster than the molecules of air medium. But it takes more energy to start the vibration. The same vibration would take more energy to start moving than in the air.
Sound In Solids– In solids are even tighter and closer together linked by chemical bonds so the wave travels even faster than it does in either liquid or air, but again just as in water, you need quite a lot more energy to start the wave at the beginning than air.
Another important influence on sound waves and how they travel is the temperature of the water. Warmer surface water in the ocean is less dense and so sound traveling through the water to the surface will refract and becomes trapped, a phenomenon referred to as a surface duct.
Hydrophone Water Microphone
Now that we know how sound waves travel through water and how water is affected by water and the difference between the sound in air and water, let’s talk about how to record that sound.
Just as a microphone can collect sound in the air a Hydrophone can collect acoustic signals underwater. Most hydrophones are produced from a special property of certain ceramics that can produce a small electrical current when subjected to changes in underwater pressure. Hydrophones are used in many applications:
- Environmental monitoring
- Navigation/positioning systems
- Underwater exploration
- Towed arrays
- Deep ocean operation
When submerged in the ocean, a ceramic hydrophone produces small-voltage signals over a wide range of frequencies as it is exposed to underwater sounds transmitting from any direction in the ocean.
By amplifying and recording these electrical signals Hydrophones can measure ocean sounds with great precision. Omni-directional and Hemi-directional hydrophones pick up sound from a particular direction and can be used to track fish movements for thousands of miles for oceanographic studies.
Piezoelectric material is ideal for making hydrophones. They can change their form and help generate an electrical potential in response to mechanical or external pressure changes. Does it sound familiar?
Well, they should. Piezoelectric microphones or Contact Mics pickups need contact with the sound source and sense audio vibrations through contact with solid objects. They are made for guitars and basses that are fitted with them and if you are a musician and chances you are if you’re reading this, you are you have probably used them in musical travel.
What is a Bioluminescent Ocean?
Bioluminescence Ocean is a phenomenon occurring when one-cell organisms called dinoflagellates are disturbed by ocean waves & movement produces a chemical reaction using compounds combined with oxygen to emit light used as a defense mechanism against predators & adding a blue-green glow .…………………………………………………………….. Read more
What is a Piezo Pickup
Piezoelectric Guitar Pickups are usually located inside the bridge of the guitar. Piezo pickups work by picking up the actual vibrations of the string and the instrument using A piezo-electric pickup that uses pressure to create a current.
Like this one called LR Baggs X-Bridge Standard Strat Guitar Piezo Bridge Pickup, Gold found on Amazon. The current is in close relation to the frequency of the source. Contact microphones based on Piezo materials that are passive and high-impedance, which can make them sound ‘tinny’ without a matching preamp.
The speed and distance at which a sound wave travels through water will be proportional to the pressure changes, which will determine the nature of the electrical output that is transmitted.
Hydrophones can be used to collect acoustical data from impacts from both human activities and natural processes, such as underwater volcanoes, earthquakes, and icequakes on the marine environment.
The applications of hydrophones typically will involve a known positioning of the hydrophone on the seafloor or parallel to a boat underwater.
Sound waves traveling in from various distances will reach the hydrophone at different times, and this time difference helps locate the source and distance of a signal wave. Collecting real-time data.
Sound Speed and Refraction Follow Water Temperature
While sound travels faster in water than in air the distance that sounds waves travel is dependent on the ocean temperature and pressure. As the 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. Sound can travel as fast as 1500 meters per second.
As a whale is traveling through the ocean and calls out to his pod, he produces sound waves that move similarly to ripples through the water. As the whale’s sound waves travel through the water their speed decreases with decreasing 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 changes in temperature and pressure which occur 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 most of its energy. In fact, hydrophones, or underwater microphones, if placed at the proper depth, can pick up whale songs and manmade noises from many many miles from one side of the ocean to the other.
Using deep-sea hydrophones being placed on the seafloor can provide a soundscape of noises in data that are carried back to shore areas studied. This can open up a whole new world of information and knowledge that scientists have never used before.
In July 2015, MBARI researchers installed a broadband hydrophone on Smooth Ridge, about 30 kilometers (18 miles) from shore and 900 meters (3,000 feet) below the sea surface. Since that time, signals from the hydrophone have been relayed back to shore in real-time. Relaying information 24 hours a day, using MBARI’s cabled ocean observatory, this type of equipment is used on upcoming space missions to Mars.
These Hydrophones are very sensitive and don’t compare much to anything we ever heard. Most adults at least those who haven’t attended too many rock concerts can hear sounds from about 20 Hertz (the low rumble of an earthquake) up to 16,000 Hertz (the high-pitched buzzing of a mosquito). However, the new hydrophone can pick up sounds from 10 to 128,000 Hertz.
Most of these units come with a microphone and camera similar to setups like Ricoh Theta V 4k 360 Spherical Camera with TA-1 3D Audio Microphone for Theta V and TW-1 Underwater Housing for Theta Spherical Cameras (V, S & SC) found here on MyWaterEarth&Sky and sold on Amazon
The sound of the oceans of the world has not been studied up until now. Distinctive sounds that are picked up with a deep-sea Hydrophone like low frequency sounds that sort of resemble a semi-truck downshifting are Blue Whales 10 Hertz calling to each other and communicating.
Why is the Ocean Different Colors?
H2O absorbs all colors except in the Blue part of the light spectrum.
The deeper the H2O the bluer that’s reflected
In the shallower ocean, sunlight penetrates H2O creating phytoplankton & reflecting green color
Other hues can be created as light bounces off floating sediments & particles .…………………………………………………………………………. Read more
One of the greatest advantages of sound in the Biological view is that there is so much more of it than people realized ever before and it’s able to travel soo well. This new type of Sound Science is able to provide huge amounts of data from long distances away.
This type of information is important for many different reasons. In deep water marine creatures can hear sound from great distances. The songs of Humpback Whales can be amplified across vast oceans of the world.
How Do You Get Out Of a Rip Current?
Stay Calm
Conserve energy
Don’t swim against the current
Stay afloat
Hold your hands up to signal help
Ride the Current in its natural circular motion to bring you back to a sandbar or waves that push you back to shore.
Or
Ride it out to deep water where the Rip will cease to exist.
Wave to Lifeguards .………………………………………………………………………………………………………………………………..Read more
References:
How far does sound travel in the ocean? from the NOAA
