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Question

I was told that lower frequency sound waves (like from a bass guitar) travel lower to the ground that higher frequencies. Is this true?
Asked by: Bill Lester

Answer

The lower frequencies of sound don't necessarily travel any closer to the ground, by virtue of their frequency. It could also be said that lower frequencies travel nearer to the ceiling. It might be said that the noise of a foghorn travels lower to the ground, but we'll discuss that in a second.

Higher frequencies tend to be more 'directional' than lower frequencies. Higher frequencies have a higher average power for any given section of the wave, than lower frequency waves. This doesn't mean they are 'louder' or have a higher peak amplitude... it just means they have higher power.

Follow me along this thought experiment. I'll assume you are familiar with the 'wave' in a stadium, whereby a line of people stand up and sit down in succession. Imagine these people, instead of getting up and down, are getting up and down on a step. The speed that the wave goes around the stadium is dependent on how fast each individual person gets up, since the next person in line has to wait for the previous person to move.

Now, let's say on two different days, you have two different waves. To make a wave with higher frequency, that is, to make a wave that goes up down more times in one second, you need the people to stand up and down very fast. They would use a lot of energy to do it. If you wanted the wave to move slower, you would tell them to take their time getting up. They wouldn't spend much energy at all. The amplitude, or the height of the wave, is going to be determined by how high the step is... the power of the wave is how much energy the people have to expend to get up and down it a number of times in one minute or second, etc.

So. Low frequencies, because of the big distance between the peaks and troughs of the wave... tend to go 'around' objects that are in their way. That is, the wave can maintain it's shape and still bend. High frequencies are narrow, because of their higher power, and very tightly packed. They have the tendency to 'bounce' off of objects in their way. Foghorns have a very high amplitude, and a very very low frequency. That way they won't be blocked by ships or rocks in the water. It ALSO means that they tend to 'bend' along the curvature of the Earth.

Similarly, in my living room, I have Bose speakers, 5 small cubes and a big bass box. The bass box I can put nearly anywhere, because the sound it puts out is low, it 'flows' around the room and seems to come from everywhere at once. The smaller high frequency speakers are harder to hear unless they're pointed right at you, or they're bouncing off a wall in your direction. It's the same reason you can hear some cars coming long before you see them, because the bass rumbles out and travels far, because it doesn't get scattered and reflected by buildings in it's way.

So, in short... the only way that your hypothesis is true, is that if you're talking about VERY large amplitudes, and VERY large frequencies, more like a foghorn than a bass guitar. I hope that helps. The lower frequencies of sound don't necessarily travel any closer to the ground, by virtue of their frequency. It could also be said that lower frequencies travel nearer to the ceiling. It might be said that the noise of a foghorn travels lower to the ground, but we'll discuss that in a second.

Higher frequencies tend to be more 'directional' than lower frequencies. Higher frequencies have a higher average power for any given section of the wave, than lower frequency waves. This doesn't mean they are 'louder' or have a higher peak amplitude... it just means they have higher power.

Follow me along this thought experiment. I'll assume you are familiar with the 'wave' in a stadium, whereby a line of people stand up and sit down in succession. Imagine these people, instead of getting up and down, are getting up and down on a step. The speed that the wave goes around the stadium is dependent on how fast each individual person gets up, since the next person in line has to wait for the previous person to move.

Now, let's say on two different days, you have two different waves. To make a wave with higher frequency, that is, to make a wave that goes up down more times in one second, you need the people to stand up and down very fast. They would use a lot of energy to do it. If you wanted the wave to move slower, you would tell them to take their time getting up. They wouldn't spend much energy at all. The amplitude, or the height of the wave, is going to be determined by how high the step is... the power of the wave is how much energy the people have to expend to get up and down it a number of times in one minute or second, etc.

So. Low frequencies, because of the big distance between the peaks and troughs of the wave... tend to go 'around' objects that are in their way. That is, the wave can maintain it's shape and still bend. High frequencies are narrow, because of their higher power, and very tightly packed. They have the tendency to 'bounce' off of objects in their way. Foghorns have a very high amplitude, and a very very low frequency. That way they won't be blocked by ships or rocks in the water. It ALSO means that they tend to 'bend' along the curvature of the Earth.

Similarly, in my living room, I have Bose speakers, 5 small cubes and a big bass box. The bass box I can put nearly anywhere, because the sound it puts out is low, it 'flows' around the room and seems to come from everywhere at once. The smaller high frequency speakers are harder to hear unless they're pointed right at you, or they're bouncing off a wall in your direction. It's the same reason you can hear some cars coming long before you see them, because the bass rumbles out and travels far, because it doesn't get scattered and reflected by buildings in it's way. The lower frequencies of sound don't necessarily travel any closer to the ground, by virtue of their frequency. It could also be said that lower frequencies travel nearer to the ceiling. It might be said that the noise of a foghorn travels lower to the ground, but we'll discuss that in a second.

Higher frequencies tend to be more 'directional' than lower frequencies. Higher frequencies have a higher average power for any given section of the wave, than lower frequency waves. This doesn't mean they are 'louder' or have a higher peak amplitude... it just means they have higher power.

Follow me along this thought experiment. I'll assume you are familiar with the 'wave' in a stadium, whereby a line of people stand up and sit down in succession. Imagine these people, instead of getting up and down, are getting up and down on a step. The speed that the wave goes around the stadium is dependent on how fast each individual person gets up, since the next person in line has to wait for the previous person to move.

Now, let's say on two different days, you have two different waves. To make a wave with higher frequency, that is, to make a wave that goes up down more times in one second, you need the people to stand up and down very fast. They would use a lot of energy to do it. If you wanted the wave to move slower, you would tell them to take their time getting up. They wouldn't spend much energy at all. The amplitude, or the height of the wave, is going to be determined by how high the step is... the power of the wave is how much energy the people have to expend to get up and down it a number of times in one minute or second, etc.

So. Low frequencies, because of the big distance between the peaks and troughs of the wave... tend to go 'around' objects that are in their way. That is, the wave can maintain it's shape and still bend. High frequencies are narrow, because of their higher power, and very tightly packed. They have the tendency to 'bounce' off of objects in their way. Foghorns have a very high amplitude, and a very very low frequency. That way they won't be blocked by ships or rocks in the water. It ALSO means that they tend to 'bend' along the curvature of the Earth.

Similarly, in my living room, I have Bose speakers, 5 small cubes and a big bass box. The bass box I can put nearly anywhere, because the sound it puts out is low, it 'flows' around the room and seems to come from everywhere at once. The smaller high frequency speakers are harder to hear unless they're pointed right at you, or they're bouncing off a wall in your direction. It's the same reason you can hear some cars coming long before you see them, because the bass rumbles out and travels far, because it doesn't get scattered and reflected by buildings in it's way.

So, in short... the only way that your hypothesis is true, is that if you're talking about VERY large amplitudes, and VERY large frequencies, more like a foghorn than a bass guitar. I hope that helps.
Answered by: Frank DiBonaventuro, B.S., Physics Grad, The Citadel, Air Force Officer



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