Why is sound lagging?
Sound lag refers to the short delay between when an audio signal is produced and when it is heard by the listener. This delay is caused by the fact that sound travels at a finite speed, around 340 m/s at sea level, through air. Therefore, if a sound is produced at a distance from the listener, it will take some time to travel through the air before it arrives at the listener’s ears and is perceived.
This phenomenon occurs because sound is a mechanical wave that requires a medium like air to travel through. The sound wave has to physically propagate through the air from the source to the listener, which takes time. Light, on the other hand, can travel extremely fast at the speed of 300,000,000 m/s. This massive difference in propagation speed is why we perceive light instantly but sound has a noticeable lag.
The delay between the initial production of a sound and when we hear it depends on the distance between the source and listener. The further away the listener is, the longer the sound takes to reach their ears, resulting in a more noticeable lag. This physics of sound underlies many common experiences, like hearing thunder after seeing the lightning.
The Speed of Sound
Sound travels at a finite speed through a medium like air or water. The speed of sound depends on the medium it is traveling through and attributes like temperature. According to the Wikipedia article on the speed of sound, at a temperature of 20°C (68°F), the speed of sound in air is approximately 343 meters per second (1,125 feet per second). This equates to around 1,235 km/h or 767 mph.
The speed of sound can vary greatly depending on the medium. For example, the speed of sound in water is around 1,481 meters per second at 20°C, over 4 times the speed in air. Other materials like steel and diamond allow sound to travel at speeds over 5,000 meters per second.
Light Travels Faster than Sound
One of the key reasons that sound lags behind light is that light travels incredibly fast – at 299,792,458 meters per second in a vacuum, commonly referred to as the speed of light or c. This makes light the fastest thing in the universe. By contrast, sound travels quite slowly. At room temperature, the speed of sound in air is only 343 meters per second, or about 1 million times slower than light.
The enormous difference in the speeds of light and sound accounts for many observable phenomena, from lightning being seen before thunder is heard, to the longer delay for seeing and hearing more distant events. This difference underlies the lag between seeing and hearing the same event.
The Reason for the Speed Difference
The key difference between light and sound is that light is an electromagnetic wave, whereas sound is a mechanical wave. Electromagnetic waves such as light can travel through a vacuum at a constant speed of around 300,000 km/s. Mechanical waves like sound require a medium such as air or water to travel through, and propagate by the compression and rarefaction of molecules in that medium. The speed of sound therefore depends on the type of medium it is traveling through.
Light can travel incredibly fast through a vacuum because electromagnetic waves consist of oscillating electric and magnetic fields, so they can propagate without a medium. Sound is produced when an object vibrates and causes variations in pressure and density in the surrounding medium. These compressions and rarefactions can only travel through matter as fast as the molecules can transmit them. So the limiting factor for the speed of sound is the inertia of the medium it moves through.
In summary, light can travel over a million times faster than sound because it can move independently as an electromagnetic wave, whereas sound relies on the properties of physical matter to transmit its mechanical vibrations.
(Source: https://www.quora.com/Why-is-light-faster-than-sound)
Observing the Lag
One of the most common examples of observing the lag between light and sound is during a thunderstorm. When lightning flashes, the light reaches our eyes almost instantly. However, the resulting clap of thunder travels much slower, at the speed of sound. As a result, we see the lightning flash first, and hear the thunder several seconds later. The delay between the flash and the bang allows us to appreciate the significant difference between the speeds of light and sound.
Specifically, light travels at about 186,000 miles per second, while sound travels at around 767 miles per hour. So light can circle the globe 7.5 times in one second, while sound would take over a week to travel that far. This enormous speed difference is why we observe lightning first, and hear the delayed thunder afterwards (Source: https://www.quora.com/If-light-travels-faster-than-sound-than-why-is-there-no-delay-between-listening-and-seeing-things). The greater the distance, the longer the lag between seeing the lightning and hearing the resulting thunder.
Other Examples
There are many examples from everyday life that illustrate the sound lag phenomenon. One common example is watching a baseball game. When the batter hits the ball, spectators first see the impact between the bat and ball before they hear the “crack” of the wood colliding. The sound takes longer to reach the stands, so there is a brief delay between seeing and hearing the event.
Fireworks displays also showcase the lag between sight and sound. When fireworks explode in the sky, bright flashes of light are visible instantly. However, the loud boom from the explosion takes longer to travel through the air. Viewers see the visual explosion first, followed by the delayed thundering sound it creates.
According to the Encyclopedia Britannica, the speed of sound is approximately 767 miles per hour at sea level. Meanwhile, light travels at 186,000 miles per second. This immense difference in speed accounts for the lag between seeing and hearing distant events.
The Effects of Sound Lag
One of the main effects of sound traveling slower than light is difficulty syncing audio and video. This is because the sound from an event reaches our ears slightly later than the light reaches our eyes. For example, when watching a fireworks display, you’ll first see the flash of light from the explosion, followed by the sound reaching your ears a fraction of a second later. This delay between seeing and hearing an event is due to the slower speed of sound compared to light (Zavala, 2015).
Another effect of sound lag is echoes and reverberation. When sound waves reflect off surfaces like walls, ceilings, or mountains, the reflected sound waves reach our ears slightly delayed compared to the direct sound. This causes a repetition or echo of the original sound. The delay between the direct and reflected sound waves produces the effect of reverberation as the sound persists and decays in an enclosed space (Zavala, 2015). Proper acoustic treatment can help reduce excessive reverberation and echo.
Compensating for Sound Lag
Sound engineers use various methods to compensate for sound lag when recording audio separately from video. One technique is to add a delay to the audio track in post-production so that it syncs up correctly with the video (source). They measure the lag between the audio and video tracks and then shift the audio by that exact amount to realign it.
Video editors also employ techniques to fix sound lag (source). If the camera records reference audio that is out of sync, they analyze the waveform of the reference track and match it to the separately recorded high-quality audio track. This aligns the good audio with the video automatically. Editors can also manually slide the audio track left or right until it visually lines up with the video.
Theoretical Limits
The speed of sound has an absolute upper limit determined by the laws of physics. According to research by physicists at the University of New South Wales, this limit depends on two fundamental physical constants – the fine structure constant and the ratio between the Planck constant and proton mass (https://physicsworld.com/a/fundamental-constants-set-upper-limit-for-the-speed-of-sound/). Their calculations show that the maximum possible speed of sound in any medium is about 36 km/s. This is still far below the speed of light in a vacuum, which is about 300,000 km/s.
The reason sound can never reach light speed is that sound propagation requires particles to physically collide and interact with each other. But nothing with mass can reach the speed of light based on Einstein’s theory of relativity. So there is a firm cap on how fast the particle interactions enabling sound transmission can occur, irrespective of the medium (https://www.quora.com/What-dictates-the-limit-to-the-speed-of-sound-and-why-is-it-the-same-speed-everywhere).
In summary, the theoretical limit to the speed of sound is slightly below 36 km/s due to constraints from physics constants and properties of matter. This maximum speed is still far lower than the speed of light due to reliance on particle interactions for sound propagation.
Conclusion
In summary, the reason sound lags behind light is due to the difference in the speed of propagation. Light travels extremely fast at 186,000 miles per second, while sound travels at a much slower speed of 767 miles per hour. This massive difference in propagation speed is why when we observe distant events like lightning or fireworks, we will always see the light before we hear the sound. The laws of physics dictate that electromagnetic waves like light will travel faster than mechanical waves like sound.
To reiterate the physics, light can travel so fast because it is transmitted as an electromagnetic wave that does not require a medium like air or water. Sound, being a mechanical wave, relies on particles bumping into each other to propagate through a medium, which limits its speed. This fundamental difference in how the two types of waves travel results in the observable lag between seeing and hearing distant events.
While sound’s slower speed can cause lag, it also provides a unique way of observing and measuring our world. With careful calculations, the time delay between seeing and hearing faraway events can help determine the distance to lightning strikes and exploding stars. The speed of sound is also crucial for technologies like sonar and ultrasound imaging. So while light may travel faster, sound continues to provide value in revealing our world.