How far does sound travel in water? Well as we’ll see today, very loud sounds can travel hundreds of miles in water in a perfect (physics-style) environment. And in the ocean, due to sound wave reflection, sound can travel even farther. In fact, whale sounds have been recorded several thousand miles away from their source.
So let’s get into it.
The Inverse Square Law
In order to understand how far sound travels in water, you must first learn the concept of the inverse square law. I’m not going to confuse you with physics definitions from my college days, so let’s just talk in layman’s terms.
Sound is one of the forms of energy that is generated from a single point and travels out from that point in a spherical fashion. When someone screams, you can hear the scream if you are standing in front of the person, behind them, right of them, left of them, above or below them. The noise travels in all directions.
And if you could see the sound waves, they would make a giant sphere around the screaming person growing and moving away from them.
Total energy stays the same
Here’s the phenomenon of the inverse square law. The total energy of the sound stays the same. So as the sphere gets bigger, that sound energy is spread out over a larger and larger area, which basically just means it gets quieter and quieter the further from the source you are.
OK that’s really all you need to understand.
Sound emanates from a single source and goes out into the world in an ever-growing sphere of sound waves that results in the sound getting quieter as you get further from the source.
Can Sound Travel Infinitely Far in Water?
So here’s the thing. Sound could hypothetically travel infinitely far in the right environment.
As the sound waves get further from the source they get quieter and quieter, but they never reach zero.
If you were listening in on the sound, eventually you wouldn’t be able to hear it. The threshold for human hearing is about 10 decibels. At some point the intensity of the sound would fall below the level where a human could perceive it, but it would still be there.
So again, hypothetically, there could be an environment where sound could travel infinitely far in water, but the intensity of the sound would fall below a perceptible level once you reached a sufficient distance from the source.
But in real environments, sound doesn’t travel forever.
Sound Doesn’t Travel Forever in Water in the Real World
The reality is that as sound travels out away from its source, some of the energy gets transferred into other types of energy. In my article on the sound absorption of different materials, I discuss this in mild depth.
The gist is that when sound waves run into objects, the object will reflect some of the sound energy, allow some of the energy to pass through it, and absorb some of it. Typically the energy absorbed by an object turns into heat.
So if a bomb explodes underwater, some of the sound energy will encounter underwater creatures, objects and the sea floor. When it hits these objects some of the energy will absorbed and ultimately lost.
Eventually all of the sound energy will be absorbed by something.
Answering the Question “How Far Does Sound Travel in Water”?
It’s not really practical to discuss how far the last remnants of a sound wave will travel. Perhaps you could run an expensive experiment, gather data, and find a respectable answer.
Unfortunately, I don’t have the means to run such an experiment.
So I want to answer a slightly different question.
How far would sound travel in water before becoming imperceptible to the human ear?
This is a question we can actually answer without a fancy experiment, using the inverse square law. First, let me show you a quick example and then we’ll go into some more details so you can answer this question for yourself.
Example: 100 dB source
Let’s do a quick example where the intensity of the sound at its source is 100 decibels. Let’s just say you have really loud bluetooth speaker that can play music underwater and it hits 100 dB when you crank the volume up.
The inverse square law says that the intensity of the sound at a distance “x” is 1 over that distance squared.
In order to use this information we need to understand the decibel scale a bit better. First, decibels are measured in Watts/meter squared. Second, the decibel scale is logarithmic. 50 decibels is ten times as loud as 40 decibels, which is ten times as loud as 30 decibels.
This means, first and foremost, that our “distance” from the source is measured in meters.
If we stand 2 meters away from the source, the intensity is 1/4 (1/2×2) and if we stand 3 meters away the intensity is 1/9 (1/3×3).
Note: the speed of sound actually doesn’t play a part in the inverse square law. It’s tempting to assume that since sound travels FASTER in water that it would also travel FARTHER. This is actually not the case.
So our 100 dB source would be 10,000,000,000 times louder than what the human ear can detect (0 dB). We need only take the square root of that number to get 100,000 meters.
So a 100 dB sound would travel 100,000 meters (that’s about 62 miles) in the water before it would be undetectable by the human ear.
Sound travels farther in the ocean (and other bodies of water)
Now, keep in mind that this calculation is true for perfect environments. And by perfect environment I mean an environment that doesn’t reflect or absorb sound and it has no noise pollution.
But in real world environments, sound energy IS reflected, absorbed and has noise pollution. The ocean for example, will make sound travel farther. This is because the sound waves will tend to retain most of their energy in the ocean as they bounce (or reflect) off the ocean floor and surface.
In the ocean, sound waves can travel considerably farther than the inverse square law would calculate.
In real world environments, sound does actually travel farther in water that in the air. Water just does a better job of not losing the sound energy. Sound is reflected more and absorbed less in water.
In fact, whale sounds have been recorded thousands of miles from their original source in the ocean.
Conclusion: How Far Does Sound Travel in Water?
So, how far does sound travel in water?
It depends first on how loud the source of the sound is. For a 100 decibel sound we saw that it would travel nearly 200 miles before it would be undetectable by the human ear (assuming none of the sound energy is reflected or absorbed). Here’s a quick table with some more distance values:
|Intensity at source||Distance until undetectable|
|100 dB||100,000 meters (about 62 miles)|
|90 dB||31,622 meters (about 20 miles)|
|80 dB||10,000 meters (about 6 miles)|
|70 dB||3,162 meters (about 2 miles)|
|60 dB||1,000 meters (less than 1 mile)|
|50 dB||316 meters|
|40 dB||100 meters|
|30 dB||32 meters|
|20 dB||10 meters|
|10 dB||3 meters|
|0 dB||0 meters (already undetectable)|
And in the ocean, sounds can travel much farther than that since the sound energy is reflected by the ocean surface and floor.