Andrew Smith
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Except for inefficiencies, no. There is no particular reason for heat being created when sound is made. But when the sound wave decays the energy in the sound is turned into heat.THAT is when the energy is released as heat.
oyubir
Generally speaking, nothing does not produce some small amount of heat.
The wave propagation would have to be perfect (and there is no such thing as perfection, as you know) for it to propagate without heat production.
Even more: no form of energy on Earth do not end up mainly in form of heat eventually (you could argue that EM wave of Hitler opening of 1936 Olympics are not heat even after they reached Orion. But that is negligible compared to the energy emitted)
Reason why sound wave attenuates is because of damping of the support (note, I am not talking here about diminution of intensity with distance, inversely proportional to square distance. That is just the wave spreading on a bigger and bigger surface. I am talking of the attenuation that makes sound less efficient than this 1/r² rule. That make sounds attenuate even on an unidimensional support — if you speak into a pipe, or into a tin can connected by a string to another one: no spreading; without attenuation, sound intensity should remain constant all along the pipe or the string. Yet you can't speak to your buddy in China that way, because sound energy is lost)
Air for example, have a viscosity. So part of the movement induced by the pressure wave is damped by it; the energy of the sound is turned into friction energy, that slightly heat the air.
But of course that is negligible.
Even a loud hifi system hardly produces more than 20W of sound energy (they display far more for the big ones. But they cheat by the invention of "musical watts" which is not a thing; they display a maximum capacity, which is not what they constantly emits, far from that, unless you listen exclusively a monotone ultrasound sine; and they don't take into account efficiency of speakers — another way to produce heat instead of sound, btw).
So, that means that 20W of energy is turned into heat eventually. I mean, at a certain distance, you can't hear the music anymore (even if not far enough for the 1/r² thing to low it to the point where you can't hear it — the 1/r² is "only" a diminution of 3dB each time you double distance. That is not enough to explain why you can't hear it from a distance). Because 100% of the 20W are turned into heat.
In a closed room, it is more complicated, because of echo (sound bounces on the wall). But that also produces heat (bounce is not perfect).
Switch off the music, and you instantly cease to hear it, right? That tells you how fast 100% of the sound wave is turned into heat. If it wasn't, sound would continue to bounce on the walls and you'd hear it after the source is gone.
So, it is less than a light bulb (whose energy, in a closed room, eventually turns into heat also: switch the ligtht off, and it is instantly dark. Ligth energy does not continue to exist bouncing on walls and object. It is quickly turned into heat).
Tl;dr: yes, if your sound system consumes 23,45 W of electricity, then, it produces, eventually 23,45W of heat. Some directly (Joule effect) some indirectly because if produces a sound wave that is eventually turned into heat.
Fireman
Yes, sound waves can generate heat. In fact, sound waves almost always generate a little bit of heat as they travel and almost always end up as heat when they are absorbed. Sound and heat are both macroscopic descriptions of the movement of atoms and molecules. Sound is the ordered movement of atoms and molecules in rapid waving patterns. Heat is the disordered, random, movement of atoms and molecules. Therefore, all you have to do in order to turn sound into heat is transform some of the ordered movement of the atoms and molecules into disordered movement. This effect always happens to some extent. This effect happens a lot whenever the sound wave encounters irregularities as it travels.
For instance, dust particles in air are irregularities that randomly interfere with the vibrating motion of some of the air molecules that make up the sound wave. The dust particles mess up some of the ordered motion, and therefore convert some of the sound to heat. As another example, the rough surface of an object constitutes a collection of irregularities that the sound wave encounters. Therefore, when a sound wave hits a rough surface, the motion of the air molecules gets scrambled up a bit. Note that the air molecules already have a motion that is somewhat disordered. In other words, air through which sound is traveling already contains some amount of heat. When some of the sound wave is converted to heat, the motion of the air molecules becomes more disordered and the amount of heat increases.
The ordered movement of atoms is also made more disorderly when sound travels through acoustically absorbent materials. Materials can be made absorbent by embedding an array of little irregularities directly into the material, such as air bubbles. For this reason, materials that are soft and porous, like cloth, are good at converting sound to heat. The sound is said to be "absorbed" or "lost" when it is converted to heat inside a material. Even without irregularities, a material can be highly absorbent if the atoms and molecules that make up the material cannot slide past each other smoothly. In this case, an atom or molecule that is trying to participate in the ordered vibrational motion of the sound wave roughly slides past the neighboring atoms or molecules that are off to the side, such that motion gets diverted in sideways directions rather than continuing in the forward direction as part of the sound wave. The ordered motion therefore becomes disordered. You can think of it as a kind of internal friction that all materials posses to some extent. In this way, some of the sound energy is converted to thermal energy. All materials, even air, have some amount of resistance to smooth atomic/molecular sliding and therefore are somewhat absorbent to sound.
In summary, sound waves always generate a little heat as they travel and they ultimately almost always end up completely as heat when they are absorbed by materials. However, the amount of energy carried by sound waves is very small, so that the amount of heat they generate is typically insignificant. In short, cranking up the volume on your speakers is a terrible way to try to heat up your room. Yelling at your soup does indeed warm it up, but the amount is far too small to be noticeable.