The energy of sound

[alexbarwell]

Thanks Ciro, looks like someone has done their homework.
An object in a vacuum does produce sound, but does not have a suitable medium to carry it. (granted this is a bit off topic anyway)
The Bel and deciBel scale is always a relative measure typically 10log10(input/output) and is only quantified when quoted wrt a defined value, but otherwise yes. As for transducers to recover this sound energy, a large diaghram studio mic with such a sound level would not last five seconds, but the output could be expected to be in the territory of mW recovered. Don't think this is a new area to explore as microphones have been developed for over 80 years and have come a long way, but as a measure line level (0dBu) would drive headphones comfortably, but a typical dynamic (develops signal power from the soundwave)microphone level will produce -60dBu, or about 1 millionth, you might get -30dBu from a phenomenal audio energy source.
Got a way to go to charge batteries from this, bit like running your microwave from an exercise bike, suddenly we are looking at the bleak side of energy recovery.

[Conceptual]

Someone tell me how the stove that I linked to on the front page can generate enough electricity to run a 120v/30A outlet, but everyone still thinks that there isn't enough to recover. If wood burning at a normally aspirated state can generate that much electricity, why can't a V8 screaming at 19000RPM make enough to charge the KERS batteries?

Thanks!

[Ciro Pabón]

Well, I don't know about the stove, I don't have too much time, I'm starting the year and have a lot to do...

You see, I assumed a 100 dB sound source (measured at 1 meter from the source): that's a pretty loud source, if I'm not mistaken.

Unless I got everything wrong, I got around 500 watts from this kind of source.

You say you get 30 amperes at 110 Volts. Not taking in account (again) that AC is a wave, this amount of electrical energy means around 110*30 = 3300 Watts.

That's not too far from the 500 watt I got (it's six times larger).

Remember that we're talking logarithmic scales when we measure in decibels (because our ears are sensitive to such a large range of energies Mr. Bell used a logarithmic scale).

So, a source six times as large as the one I assumed is (more or less, calculating in my head) an engine that gives you a reading of 110 dB at 2 meters.

That would give you around 3000 watts, not far from 30 amperes at 110 volts, assuming no losses in the sound recovery system.

Actually, 30 amperes at 110 volts, AC, it's more like 0.8*30*110 = 2500 watts because (again) when we talk about AC we're talking of a wave.

That's enough to drive a stove, but I think is not enough to drive a KERS, because 2500 watts are like 3 Hp, give or take.

The fact is that the energy of sound is very low compared with the energy of brake or exhaust heat.

Simple: there is no way you're going to heat anything through sound as much as a brakepad heats.

As Alexbarwell explains, if muffles and brakepads managed the same level of energy, you'll need a huge cooling system to hear heavy rock at full volume. You can see that he estimates that a mic manages milliWatts... Just check the diameter of a mic wire: it's not like a wall socket wire.

Of course an amplifier takes those milliwatts and then throws watts at you, but a sound system does not manage hundreds of thousands of watts, which is the energy that a braking system handles.

I repeat: the apparent huge energy of sound is in our mind. I think I'm going to hear "Seek and destroy" again, btw. After all, Metallica has such energy that I'm sure you could drive any stove you wish with the energy of the audience... Check at 4:40: that's like a couple of Gigawatts.

Can this sound make a car go faster? You bet! Actually, you don't need a KERS system: just the loudspeakers and some inspiration is enough.
[youtube]http://www.youtube.com/watch?v=wLBpLz5ELPI[/youtube]

[alexbarwell]

Getting a bit sidetracked, but was it Led Zepp, or The Who with the record for the loudest band on the planet?

[Ciro Pabón]

Well, that's a very disputed (and mocked) title in this planet. However, outside the planet, Disaster Area holds the title, because their concerts can devastate entire planets.

"So loud is this band that the audience usually listens from the safe distance of thirty seven miles away in a well-built concrete bunker."

I've heard Doctor House (the one in the TV series) saying a couple of times what every Formula One driver would like to do with their KERS: "Let's turn it up to eleven!" in a reference to amplifiers that go beyond 10 (which nowadays are more and more common).

Fender Champ 1948 amplifier: you can go up to twelve!

[vyselegend]

I innitialy asked spontaneously a naive question, and ended having a nice time reading lots of stuff!

I love F1tech! This is the only place I know where you can learn more on hard rock, space, and advanced technologies by asking something obvious about a classic engine. Thanks everyone.

[Agerasia]

Hi,
The exhaust manufacturer Micron had a novel idea to allow full race systems to meet noise regs. If you can get the sound pulses to collide you can significantly reduce the noise without having an impact on power. Unfortunately the exhausts didn't catch on as they were ugly but new designs in the headers and tail do something similar on modern bikes. They also inject fresh air into them to meet emissions regs, but that's another story.

[alexbarwell]

Thanks for the hitchikers ref ciro, although disaster area never got a mention in the radio series, extended a couple of years ago up to 13 solid hours.
Back on the subject (briefly) Agerasia I think is referring to tuned lengths/resonance/wavelength tuning - as a pressure wave from exhaust stroke travels down, there is a reduced pressure following in its wake, if this coincides with a following exhaust stroke, the idea is the low pressure phase will help to more effectively evacuate that combustion chamber requiring less pumping effort. The issue being optimising the tuning across the rev/frequency band concerned. Also tuned 'expansion' boxes on 2-strokes are there for noise control AND power development reasons, so the next spotty moron in the neighbourhood that butchers his moped exhaust in the quest for more power deserves everything coming his way.

[Miguel]

Hello everybody,

I recall that Renault advertised its RS23 (year 2003, the one with a 111.5º V) at around 140 dB (probably at 1m), so that Ciro is off by some decibels indeed. And yes, this is almost as loud as an airplane. Oh boy, do I remember the day I first went to Montmelo. And yes, although I'm 27, I've seen the Who live, and they are not as loud*. Not even when Daltrey screams in "Won't get fooled again", although that one has another kind of power**.

Finally, I've been doing some browsing in order to find some stuff in thermoacoustics. You see, I always hated thermodynamics, and irreversible processes more than any other branch, but now I find myself googling for this stuff. Anyway, here's a link to LANL's thermoacoustis site:

http://www.lanl.gov/thermoacoustics/

* The Who used to be very loud indeed. However, Pete Townshend is half deaf nowadays, and plays quieter and actively advises against listening music too loud.

** For the "young and innocent", the scream I refer to is the scream you hear in CSI: Miami after Horatio's one-liners. YEAAAAAAAAAHHHHHH

[Touring23]

Ciro Pabón, thanks for your analysis; would you please recalculate with this data:
The noise level emitted from vehicles on the circuit during the Formula-1 event, on April 4th 2004, was acceptable and caused no physical disturbance to the fans in the VIP lounges or to scholars studying at the University of Bahrain’s Shakeir Campus, which is only 1.5 km away from the circuit. The sound-intensity level (SIL) recorded on the balcony of the VIP lounge was 128 dB(A) and was 80 dB(A) inside the lounge. The calculated SIL immediately outside the lecture halls of the University of Bahrain was 70 dB(A) and 65 dB(A) within them.
http://www.sciencedirect.com/science?_o ... 5c291cefc2

Perhaps using only the area of a hemisphere (ground influence)?

*edit* I'm doing something wrong:
128 dB @ (50 meters?)
w1=6.31 J/m^3
I =2145 W/m^2
Area of a 50m hemisphere = 15,708 m^2
2145 W/m^2 * 15,708 m^2 = 33.7x10^6 Watts?!

[pitlaneimmigrant]

An object in a vacuum does produce sound, but does not have a suitable medium to carry it.

If a tree falls in a vacuum...

[ESPImperium]

Ciro Pabón - You have it right, Metallica and Guitar are another 2 special areas of my life you have struck a chord with me.

If you take my Mesa F30 guitar amp and my old Laney LC15-110 (Blew up in flames) amps, if you ran both amps into the same speaker at maximum level, the variance in volume isnt double, its infact arround 3dB more.

However, in electronics, it can be a diffrence in volume that is produced by diffrent valves/tubes and also diffrent aproaches to the way sound is produced.

However, if you were to produce a KERS system for noise, the only physical limitation would be how the sound clips the input device. As first you would probably have to compress the signal ironing out the spikes and troughs, then you would be able to convert this into electrical energy that could be charged in a battery or a super-capasitor.

And even the best compressors on tha market (Keeley Compressor [for me that is]) is a low lever comprssor, and would need the inpot device for it to be placed in a area that wouldnt clip the compressor.

Creating a worthwile energy source from sound isnt exactly how id like to get energy from KERS.

Sorry if i have been talking a lot of brownies!!!

[Scania]

Just to add to the confusion, imagine running the same engine in vacuum, there would be no sound whatsoever, right? Does that mean less losses?

no, the sound is still here but won't send out only.

[hecti]

Just to add to the confusion, imagine running the same engine in vacuum, there would be no sound whatsoever, right? Does that mean less losses?

No, there is still sound been made (ie vibration) but in space/vacuum there is nothing to vibrate (there's apparently 1 hydrogen atom per cubic foot of space) so unless one of those atoms finds its way into your ear or you put your ear right in the exhaust gasses(which i don't recommend) then you aren't gonna hear anything.

[riff_raff]

Acoustic energy is put to good use increasing power in F1 engines, through the use of acoustically tuned intake and exhaust pipe lengths. The noise your ears "perceive" from an F1 engine is due to the frequency and amplitude of the exhaust pressure pulses emanating from the exhaust pipe exit point, propagating through a dense fluid atmosphere, and striking your eardrum membrane causing it to vibrate.

This acoustic energy is most definitely energy lost from the engine. The "loudness" of the noise is generally a function of the blowdown energy going down the exhaust pipe. And for F1 engines with very early exhaust valve opening events, the initial blowdown pressure can be quite high.

But, as others have noted, it's all about how noise is perceived. Check out Lotus' active noise cancellation technology:

http://www.grouplotus.com/managedcontent/view/44