Thoughts About Sound

I started reading “Tell No One” by Harlan Coben last night (it was adapted into a great French movie by the way), and I came across this paragraph in chapter one that really got to me:

“But I remembered how the laugh and the howl and the splash would ripple and echo in the stillness of our lake, and I wondered if ripples and echoes like those ever fully die away, if somewhere in the woods my father’s joyful yelps still bounced quietly off the trees. Silly thought, but there you go.”

It was only the first chapter, but it stuck in my brain deep enough that I had to stop reading after I finished the chapter.

Now, I know that it is kind of a silly thought knowing that sounds do in fact dissipate, but what if conditions are ideal. What if you make a sound in a perfect room that does not absorb any of it; will the sound keep going forever? The sound will bounce off the walls, but what will happen next?

Will it bounce back as the same sound that bounced in?
Does it just expand enough that it’s so faint that we can’t hear, but still exists?

No matter how cool I think it would be if every sound ever made was still floating around somewhere, in one way or another, up in the sky, I think it could be possible if conditions are perfect.

First, sound is a wave, but it also emanates in every direction from the source. So, the sound is expanding in every direction and therefore losing intensity just by being emitted.

Next comes the point when the sound is reflected. Now, we are assuming that the room is ideal and the wall will not absorb any of it. I believe that there is a least one example that could keep the sound alive. This is shown in my brilliant picture below.

Sound Diagram

Imagine that the circle is actually a sphere with all the “sound” lines coming from every point except from the point of attachment. When it hits the wall is where things get tricky. If the wave hits at the crest (top of the wave) or trough (bottom), it should bounce back directly to the source and then back and forth forever (in my mind) as long as the source is of ideal material.

Now, if the wave hits the wall when it’s at some other point in between the crest or trough, it will bounce in any number of directions. That’s when the sound wave gets diffused by contact of various wave pieces going in those different directions and therefore the wave is eventually destroyed.

From my example, it all depends on the relation of the distance of the wall from the source and the frequency of the sound wave. Conditions have to be extremely ideal, so I would say that even with ideal material, it is unlikely for the sound to continue. And even though this could never happen for real, the nerd in me enjoyed thinking about this problem.

I would love to hear what everyone thinks about my theory or what your theories might be.