Nova Zhang
It is a widely held belief that low-frequency sounds travel farther than high-frequency sounds. For instance, you might hear the bass from your neighbour's loud music but not the high-pitched sounds. This is because low-frequency sounds are less rapidly absorbed by the medium they travel through. In the ocean, for example, low-frequency signals are absorbed less quickly than high-frequency signals and can therefore be detected over longer distances. However, the speed of sound does not vary with frequency, and the detection of low-frequency sounds can be affected by ambient noise levels.
| Characteristics | Values |
|---|---|
| Speed of sound | Remains the same regardless of frequency |
| Low-frequency sound travel | Travels longer distances |
| High-frequency sound travel | Travels shorter distances |
| Absorption of sound | High-frequency sounds are absorbed more than low-frequency sounds |
| Detection of sound | High-frequency signals can be detected at lower sound levels than low-frequency signals |
| Sound waves | Low-frequency sounds have longer wavelengths |
| Diffraction | Lower-frequency waves are diffracted more |
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What You'll Learn
Low-frequency sounds travel further than high-frequency sounds
It is a common belief that low-frequency sounds travel farther than high-frequency sounds. This is true in the case of sound travelling through water, as low-frequency signals are absorbed less rapidly in the ocean than high-frequency signals. For this reason, signals designed to travel thousands of kilometres, such as those used in the Acoustic Thermometry of Ocean Climate (ATOC) project, use very low frequencies.
The same is true of sound travelling through air. When sound travels through a medium, it loses energy by transferring it to that medium. Lower frequencies of sound have a longer wavelength, so it takes fewer wave cycles for the sound to travel through the medium, and therefore less energy is absorbed. This is why you can hear the bass of a song throughout an entire house, but the higher frequencies seem to get lost.
However, this is not always the case. One source suggests that with very weak sounds, high frequencies may travel farther. When standing near someone listening to loud music through headphones, it is the high-pitched sounds that can be heard, not the bass. Another source suggests that high-frequency sounds may be reflected more by walls than low-frequency sounds, which could cause high-frequency sounds to travel farther in certain environments.
In general, however, low-frequency sounds are less attenuated and less absorbed than high-frequency sounds, which is why they are able to travel farther.
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Low-frequency sounds are less likely to be absorbed
It is a common belief that low-frequency sounds travel longer distances. For instance, you can hear the bass of a song throughout an entire house, but the high frequencies seem to get lost. However, some people have argued that when standing near someone listening to loud music, it is the high-pitched sounds that are audible, not the bass.
This discrepancy can be explained by the fact that lower frequencies of sound have a longer wavelength, and it takes fewer wave cycles for them to travel through a medium. Hence, less energy is absorbed by the medium. For example, a 20 Hz wave takes one cycle to pass through a piece of material, whereas a 40 Hz wave takes two cycles, and an 80 Hz wave takes four cycles, and so on. As the frequency increases, the number of cycles increases exponentially, resulting in more energy being lost.
This phenomenon is not limited to sound travelling through solids; it also applies to sound propagation in fluids, such as water. In the ocean, low-frequency signals are absorbed less rapidly than high-frequency signals, allowing them to travel longer distances while still being detectable. This is why very low frequencies are used for signals that need to travel thousands of kilometres, such as those used in the Acoustic Thermometry of Ocean Climate (ATOC) project.
Additionally, in the field of acoustics, the proper balance between sound absorption and reflection is crucial. Higher-frequency sounds have shorter sound waves and tend to be reflected back when they encounter thin objects. They also do not bend as much around barriers and can be detected at lower sound levels than low-frequency signals.
In summary, low-frequency sounds are less likely to be absorbed because they have longer wavelengths, resulting in fewer wave cycles and less energy loss during propagation through a medium. This property of low-frequency sounds enables them to travel longer distances and has practical applications in various fields, including oceanography and acoustics.
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Atmospheric absorption affects high-frequency sounds more
It is a common belief that low-frequency sounds travel longer distances. For instance, when your neighbour plays loud music, you can hear the bass (low-frequency sounds) more than the high-frequency sounds. However, when the music is played at a low volume, you can hear the high-frequency sounds better. This is because low-frequency sounds have a longer wavelength, and it takes fewer wave cycles for them to travel through a medium, which means less energy is absorbed by the medium.
High-frequency sounds, on the other hand, have shorter wavelengths and, therefore, require more wave cycles to travel through a medium, resulting in more energy absorption by the medium. This is why high-frequency sounds are absorbed more than low-frequency sounds. This phenomenon is known as atmospheric absorption or atmospheric attenuation, and it limits the distance over which high-frequency sounds can travel.
The scattering and absorption of sound waves through interference with air or water molecules cause this effect. Additionally, the kinetic energy of moving particles increases with frequency, resulting in increased energy loss or absorption at higher frequencies.
The absorption of sound also depends on the temperature and humidity of the atmosphere. For example, at a temperature of 20°C and 10% humidity, the absorption at a frequency of 8 kHz is higher than at a frequency of 2 kHz.
In the context of the ocean, low-frequency signals are absorbed less rapidly than high-frequency signals, allowing them to travel longer distances while still being detectable. This is why very low frequencies are used for projects like the Acoustic Thermometry of Ocean Climate (ATOC), which transmitted signals at 75 Hz.
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Diffraction affects low and high-frequency sounds differently
The amount of diffraction that occurs in any wave is dependent on the wavelength of that wave. Diffraction is the process by which sound waves bend around objects or blockages. When an object is smaller than the wavelength of the wave, the parts of the wave that pass the object are generally of the same amplitude and phase. As the wave passes the object, it radiates into the empty space caused by the obstruction.
Low-frequency sound waves have longer wavelengths than high-frequency waves. This means that low-frequency waves can bend around objects more easily than high-frequency waves. High-frequency sounds, with their shorter wavelengths, do not bend around most obstacles but are instead absorbed or reflected, creating a sound shadow behind the object.
Low-frequency sounds have wavelengths that are often longer than most objects and barriers in their path, and so these waves pass around them undisturbed. When the wavelength is similar in size to the object, as with low frequencies and buildings, the wave bends around the object, using its edges as a focal point from which to generate a new wavefront of the same frequency but reduced intensity.
High-frequency sounds, on the other hand, are progressively deeper into the ray optics regime. This means that they are more likely to be reflected or absorbed by objects and barriers, rather than bending around them. As a result, low-frequency sounds are often more difficult to contain in an environment, as they can spread and diffuse more easily through diffraction.
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Low-frequency sounds are used for seismic profiling
It is a common belief that low-frequency sounds travel longer distances. Lower frequencies of sound have longer wavelengths, which means it takes fewer wave cycles for them to travel through a medium, resulting in less energy being absorbed. This is why bass sounds can often be heard from farther away.
In the field of seismic profiling, low-frequency sounds are used for several purposes. Seismic reflection profiling, for example, uses low-frequency sound energy 10-150 Hz to detect impedance contrasts within the crust and upper mantle. This method provides the highest-resolution images of the structure of the crust and Moho, with features as thin as 50-100m being resolved.
Seismic reflection profiling is particularly useful for imaging the fine structure of the ocean and the structure of the earth below the seafloor. When sound waves travel through the sea, low-frequency signals are absorbed less rapidly than high-frequency signals, allowing them to travel longer distances while still being detectable. This is why low frequencies are used for seismic profiling systems to locate oil and gas reserves beneath the seafloor.
Additionally, low-frequency sound waves are essential for detecting and studying natural and anthropogenic sources of seismic activity. For instance, hydrophone arrays have been used to monitor seismic activity on the East Pacific Rise, identifying tremors and earthquakes associated with volcanic activity.
Overall, low-frequency sounds are advantageous in seismic profiling due to their ability to travel longer distances with less energy absorption, making them ideal for imaging Earth's structures and studying seismic activity.
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Frequently asked questions
No, the speed of sound does not depend on frequency.
Low-frequency sounds have longer wavelengths and are less susceptible to energy loss as they travel through a medium.
Yes, low-frequency sounds are reflected less by walls than high-frequency sounds.
Lower frequencies have longer wavelengths, allowing them to pass through objects more easily than high-frequency sounds.
Low-frequency signals are absorbed more slowly in water, allowing them to travel longer distances than high-frequency signals.
