New Energy: Audio Vibrations Create Movement Energy

[strucka]

I have idea, audio is vibrating wave of air, we know how to make energy from movement (movement energy) very loud audio can vibrate membrane and from that vibrating we can make energy (axiom of movement energy) but that quantity of energy is minor

 

[nuclear-boy]

hi,


yes that is true, and yes that energy is very minor, that is basically a microphone though, isn't it?, i wouldn't call sound a form of energy, where would the loud sound come from? there is no point generating sound by using energy and then converting that sound into energy again, is there?

 

[sophiecentaur]

A fair idea, in principle, but the devil is in the actual numbers - as in many engineering problems.
When you consider that a tiny battery in a hearing aid can give an (hearing impaired) user an audible signal in their ears for several days, you will have a qualitative idea of how much energy is actually available from sound (by thinking in reverse). An environment in which there would be enough sound energy to make it worthwhile converting it into another form ( say electricity) would be so loud as to be painful or worse.
It is, I suppose, worth considering 'extracting' the sound energy that exists inside heavy machinery but improving the actual efficiency of a machine would probably be of better value in terms of energy use. We would be talking in terms of energy quantities of the order of those used in solar lights for gardens etc. rather than providing a serious amount of electrical energy.
But don't give up on inventing novel energy conversion ideas - after all, those damned parking meters are driven by solar energy nowadays and we all LOVE them, don't we?

 

[LostConjugate]

Well, you could operate your computer with your voice instead of moving a mouse and keys.

 

[sophiecentaur]

You could CONTROL it by voice but you wouldn't be supplying the power to drive it.

 

[Borek]

This question shows up again and again. My guess is that's because of the powers installed in audio amplifiers. It is nothing unusual to see 2x100W, which suggests amount of energy that can be harvested from the sound should be of the same order of magnitude. But it is not.

Honestly - I have no idea why. The only thing I can think off is that our method of producing sound is incredibly inefficient.

 

[sophiecentaur]

You are right. Good quality sound reproduction is very inefficient compared with just rubbing your back legs together (if you are a cricket).

 

[LostConjugate]

This question shows up again and again. My guess is that's because of the powers installed in audio amplifiers. It is nothing unusual to see 2x100W, which suggests amount of energy that can be harvested from the sound should be of the same order of magnitude. But it is not.

Honestly - I have no idea why. The only thing I can think off is that our method of producing sound is incredibly inefficient.

The motion of air molecules is very erratic, a lot of kinetic energy is lost.

 

[LostConjugate]

You could CONTROL it by voice but you wouldn't be supplying the power to drive it.

I wouldn't want to try and power my computer with a hand crank, little yet my vocal cords. I am talking about a smaller amount of energy, the movement of a mouse.

 

[Borek]

The motion of air molecules is very erratic, a lot of kinetic energy is lost.

Lost? To what?

 

[LostConjugate]

Lost? To what?

Lost to us, not to the universe. :)

 

[Borek]

Explain how it is lost, I have no idea what you mean.

 

[LostConjugate]

Explain how it is lost, I have no idea what you mean.

Lost by increasing entropy. For example if you had a sealed container with 100W speaker in it you could transfer the energy in its entirety to another speaker that would not require another 100W amplifier.

 

[Borek]

Still no idea what you mean, nor how it is related to the fact that motion of air molecules is erratic.

 

[LostConjugate]

Still no idea what you mean, nor how it is related to the fact that motion of air molecules is erratic.

Using a fan to push a book off the table wastes a lot of energy.

 

[Borek]

It has nothing to do with the fact that air molecules motion is erratic.

 

[LostConjugate]

Sure it does, you use 100W to accelerate a membrane at a very high acceleration, then that energy is distributed into the air all around you, now try to collect all that KE again as it escapes in every direction as far as miles away at the speed of a bullet.

 

[Borek]

Fact that energy escapes in every direction has nothing to do with the fact that molecules motion is erratic. It is based on macroscopic properties of the medium, not on the microscopic mechanism. You don't have erratically moving molecules in solids, yet the sound travels in every possible direction, very similarly to what happens in gas.

 

[LostConjugate]

Fact that energy escapes in every direction has nothing to do with the fact that molecules motion is erratic. It is based on macroscopic properties of the medium, not on the microscopic mechanism. You don't have erratically moving molecules in solids, yet the sound travels in every possible direction, very similarly to what happens in gas.

Ok, the point is the energy is in the KE of the air molecules and is not easily collected.

 

[russ_watters]

Still no idea what you mean, nor how it is related to the fact that motion of air molecules is erratic.

Energy in moving air is lost to heat, due primarily to viscous friction in the air and absorption by objects.

In addition, sound tends to be somewhat omnidirectional, so it is difficult to capture a significant fraction of the ouput of a speaker unless you surround it.

Also, a home amplifier that delivers several hundred watts is truly earsplitting in a small room, when playing loud sounds. But when your TV speakers are delivering sound that you can talk in a normal conversation overtop of, the speakers are putting out single-digit watts of power. So it isn't just that sound is tough to capture: it is also that there just plain isn't much energy in most day-to-day sounds.

 

[sophiecentaur]

The thermal motion of air molecules has a little or no effect on the sound energy passing through it. (Although the actual speed of sound depends upon the temperature) However, some sound energy is absorbed as it propagates through air and this contributes to a bit more random motion (i.e. it raises the temperature a little bit)

 

[Borek]

Ok, the point is the energy is in the KE of the air molecules and is not easily collected.

Again, where is the erratic motion of the molecules involved? While tiny part of the sound energy is lost to the thermal energy, most of it passes as if the air was perfectly elastic. Also note that at this stage there two kinds of KE - one is KE due to sound wave propagation, other is KE due to thermal motion. They are basically not related and and should be not mixed.

The thermal motion of air molecules has a little or no effect on the sound energy passing through it.

That's what I am aiming at. In the context of sound propagation erratic motion of molecules is far on the list of the things that should be taken into account, even if - no doubt about it - together with almost perfect elasticity of collisions they are what makes the air behave the way it does. But when we are talking about the sound propagation, it is enough to concentrate on the emergent properties, like compressibility and viscosity, and treat the air like continuous medium. Mentioning erratic motion only murks the water.

 

[sophiecentaur]

If there weren't "erratic motion" of air molecules, the temperature would be zero. The speed of sound would be very small because the molecules would take a vast time to bump into their neighbours and transfer the sound pressure. (Nonsense scenario, really but I quote the example to make the point).
These ideas are much better approached in the classical way, for describing the waves and, if you need to, the kinetic model to account for the (classical) modulus and density of the gas.
An ideal gas can be treated in this way but a 'real' gas will introduce loss mechanism to absorb some of the sound energy as it passes through.

 

[Borek]

I think you are missing my point. We don't need kinetic theory of gases (be it real or ideal) to describe mathematically sound wave propagation. For that we can treat air as a continuous medium. We do exactly the same when dealing with diffusion - (almost) nobody treats diffusion as a random process based on erratic motion, what we usually do is we solve Fick equation. My guess is that granularity of the medium becomes important when the wave length becomes comparable with distances between molecules - that means at least 10 GHz frequencies.

 

[LostConjugate]

Ok I see what your saying Borek, even though the molecules motion is erratic, it does not much effect the sound energy propagation.

So the reason that the energy is hard to capture is because it speeds away in every direction at the speed of a bullet and travels through most materials.

Russ, you are correct a 100W speaker at full volume is deafening.

 

[turbo]

Loudspeakers are VERY inefficient, and some of the most accurate ones are the least efficient at converting electrical impulses to sound. I have built guitar amps with some fairly efficient speakers (maybe a few percent), but they are not particularly accurate speakers. Most of the power sent to a speaker is dissipated in the form of heat, which is why it is possible to overheat the voice coils and wreck speakers. Using such a device in reverse would create very tiny electrical impulses - useless for doing any work without amplification, so there is no advantage there.

 

[sophiecentaur]

Ok I see what your saying Borek, even though the molecules motion is erratic, it does not much effect the sound energy propagation.

So the reason that the energy is hard to capture is because it speeds away in every direction at the speed of a bullet and travels through most materials.

Russ, you are correct a 100W speaker at full volume is deafening.

No. The reason it's hard to capture is because there's so little of it!

Edit: Also, you can make very good use of Light Energy and that goes nearly a million times faster!

 

[LostConjugate]

How is there so little of it? If you run 100W through the speaker coil the magnet will move with 100W worth of acceleration. Are you saying that the conservation of energy law is flawed in speakers? Speakers don't get that hot...

 

[turbo]

How is there so little of it? If you run 100W through the speaker coil the magnet will move with 100W worth of acceleration. Are you saying that the conservation of energy law is flawed in speakers? Speakers don't get that hot...

Most loudspeakers are only about 1% efficient or so in converting electrical energy into motive force, into acoustic signal. Very linear (accurate) speakers may be even less efficient.

 

[russ_watters]

How is there so little of it? If you run 100W through the speaker coil the magnet will move with 100W worth of acceleration. Are you saying that the conservation of energy law is flawed in speakers? Speakers don't get that hot...

It's been a while since I've put my hand on one, but I think the coils do get hot!

Note that a lot of the heat is also dissipated at the amplifier.

 

[sophiecentaur]

If you put the '100W speaker' into a concrete box and had a vibrating diaphragm across a hole in the box, you could probably get a watt of kinetic energy (more, if the system were tuned / matched well. But you would be better to cut out the middle man and connect the speaker leads directly to a load.

If you are just talking about using the 'wasted' sound power in a room then you have to accept that most of it will be absorbed by walls and furnishings (or, if you're outside at Glastonbury, the rest of the world) and there's precious little available for your 'sound energy collector', which will intercept a small fraction of what was produced by the speakers. If it were a worthwhile project, don't you think that they'd have something of the sort on every airfield runway, to get the power from the jet engines and inside every big noisy piece of machinery?

And, yes, speakers can get hot enough to melt the speech coil, if you drive them too hard.

 

[turbo]

It's been a while since I've put my hand on one, but I think the coils do get hot!

Note that a lot of the heat is also dissipated at the amplifier.

I have put my hands on the speaker housings and spiders, especially in applications in which I thought I was over-loading the speakers. When I built guitar amps, I almost always built open-back designs, and when I was running inverted-chassis designs (so that the tubes were head-down in the same enclosure as the speaker) and really pushing them I sometimes ran external fans to cool stuff. Probably the most iconic tones are produced Fender 5E3 tweeds and smaller Vox amps, which can run hot if pushed.

 

[sophiecentaur]

Did you ever actually measure the current and volts applied to the speech coils, though? Did you ever run 1kHz tone at a measured 100W into them? 'Loud' music is seldom equivalent to the max power single tone situation. Even with a lot of compression, the peak to mean ratio of 'interesting' guitar sounds will be a lot less than unity - you need peaks for an edgy sound.

 

[turbo]

I rarely ever benched amps with an O-scope or with a multi-meter. My concentration was on replicating tones of iconic amps. As long as the amps were performing well, and I could tweak them to get the right tones, I didn't concern myself with minutia. I built some head-only amps, and combined them with speaker enclosures that were open-backed, partial open-backed, and closed. The closed enclosures got more of my attention WRT to waste heat. Velcro a thermocouple to the the housing surrounding the voice coil (the motor of a speaker) and watch what happens when you crank the amp. I'm a pragmatist when it comes to amp-building.