From the article here:

Really Loud Freezer

"A loudspeaker pumps sound waves (at 190 decibels, louder than a rocket launch) into the canister, expanding and contracting helium gas inside. The pressure changes chill the icebox as efficiently as a conventional freezer."

EDIT: added picture.

pV=nRT

This finally proves that freaky formulas have some real word usage.

Seen these before... if it's not a different design it basically makes a standing wave the length the the canister with one side in compression and the other in expansion. The pressure difference causes a temperature difference (as per PV=nRT) and heat moves along the gradient (then removed). As for replacing conventional regfrigerators...I highly doubt it, note how they do not give an indication of it's efficiency (like an actual number), which considering a loud speaker itself is below 2%, I doubt it's all that good.

As for louder than a rocket... I wonder if I'm ever going to stop hearing this analogy, it's bunk. If your measured the sound pressure half an inch from the rocket exhaust like they do from the speaker than I can assure you that you'll get a sound pressure level FAR in excess of 190db, likewise if you measure the SPL from the speaker at the same distance they guestimate the rocket figure you're not going to get anything even remotely approaching 190db.

Thanks for pointing this out. On the surface the statement that loudspeakers were louder than rocket exhausts was silly. I would say common sense would prove this. But this kind of sense is not common, unfortunately.

For a sound in air, the maximum possible sound pressure is limited by atmospheric pressure. At sea level (1 atm / 100 kPa), the loudest possible sound can be about 191 dB's, so surely a rocket exhaust can't be FAR in excess of 190 dB?

The pressure might be higher than 1 atm an inch away from the exhaust, however

Maybe a rocket blast is so loud it clips the air? =D

190 dB is so loud as to be inconceivable to me. Once, I had the opportunity to hear 125 dB @ 1 meter of noise (being played by a horn speaker), isolated from us in a metal room, with our ears covered by 30 dB headphones. It was still loud.

ff123

This is foolish, but I challenge the validity of the statement that the speaker generates 190 dB and is louder than a rocket exhaust. Just think about the amount of energy the rocket engines are generating and the effect they have on the air.

OK, I have two stereo amps, each generates 1,100 to 1,300 watts. I feed this into a pair of KEF 104/2's, each rated at 4 ohms and capable of handling 4,500 watts continuous energy, company specs. Now do you really believe that this speaker system is going to make the ground shake, buildings shake, rocket gantries shake and be heard miles away and at the same volume and force that the rocket engines will be heard?

My amps generate about 3 HP apiece, I think. That is a total of 6 HP, not quite enough to lift a Saturn rocket of the pad.

It seems pretty simple to me. But what do I know? I am a Liberal Arts major.

So, if you can't get much louder than 190 db, rocket engines can't be nearly that loud, because there are things much louder. When Krakatau exploded, it was heard 3,000 miles away. The pressure wave traveled around the Earth 7 times over the course of 5 days.

Or maybe I'm confused about decibels again... If the maximum pressure is 191 db or so, where is the extra energy hiding in something really loud like an exploding island?

Oh, and apparently a blue whale's vocalizations can get as loud as 188 db.

Perhaps the sound increases logrithmically up to the theoretical ~190. If it does I wonder how that little speaker could be as loud as exploding Krakatao? Could the article in PopScience be published in the right place? When stuff like that gets published in a known and responsible scientific publication I will be more able to believe it. For the time being I remain a skeptic.

190dB or not, I'd hate to be in the room if that thing fell apart

This site provides a bit more info on the 190 db sound... The sound is only this loud because the waves are being pumped into a pressurized container, if for some reason the container were to be broken open, the sound released would be much quieter.

The limit comes from the vacuum that is formed during the decompression phase of the wave. You can't get lower pressure than a vacuum, so the lower wave peak is indeed "clipped". So a rocket engine indeed clips the air If you increase the pressure of the medium, you can achieve louder sound.

In water the pressure of the medium is a lot higher than in air. 10 km below the surface you can have pretty impressive sound levels. Sound also travels much faster in water. You can also have pretty impressive sound levels in stone. Krakatau's blast wave moved mainly in the ground itself, which acted as a "speaker".

A sound wave can't possibly go around the earth a few times (like in the Krakatau case) just in the air, even the loudest possible sound would dissipate in a few hundred km's or so.

A rocket engine moves a lot more air than a speaker cone, so the area of the 190 dB'ish sound pressure is a lot bigger than with a speaker cone. The rocket engine also shakes the ground, which then propagates the sound to a great distances.

The blue whale has no problem creating 188 dB sound pressure because of the water medium. I wouldn't like to be scuba-diving in front of the whale when it releases this nightmarish howl though

If I venture in the realms of pure speculation, I wonder if a "clipped" waveform dissipates more slowly in the air than a nonclipped one. Even if the sound level can't get higher than 191 dB's or so, the air molecules still have more kinetic energy than needed to create a 191 dB sound. So, the wave travels in clipped state at maximum possible sound pressure for a while, and after losing the excess kinetic energy starts dissipating normally.

Or possibly a "square wave" is formed in the air because of the clipping

That could also explain why a rocket launch is so loud even several kilometers away, or why Krakatau's blast wave travelled around the earth. Also a nuclear bomb creates a pressure wave that reaches a vacuum during the decompression phase for the length of several kilometers, or the sound travels in "clipped state".

Edit:

Okay, I gave the subject a bit more thought and I came up with this: the sound pressure (SPL) is limited by the lower peak of the wave because of the vacuum, but the upper peak is theoretically not bound. So you can't have continuous, sine-like wave louder than ~191 dB's, but the energy travels in the upper peak of the wave, which is much farther from the "DC level" than the "clipped" lower peak. Does this make any sense?

Edit2:

Some corrections.

I think I might be mixing the physics terms "energy in a wave", "intensity of a wave" and "SPL" together in situations where they're not freely mixable. My physics book had nothing about the subject of "maximum possible wave amplitude in a given medium". Maximum energy in a mechanical wave isn't probably limited, but the amplitude of the wave most likely is due to the properties of the medium. Would someone elaborate, please?

Really interesting thread, keep the facts coming
Its kind of topical for me, I work in Ice-cream for Unilever (who acquired Ben & Jerry's a few years ago).

Would you PHYSICALLY survive a blast of 190db? I mean, I am thinking 'instantly ruined ears' <shudders>, but would that sort of volume crack your bones, and generally turn you into a gloopy blob on the floor?


More --> http://radio.weblogs.com/0105910/2004/04/15.html

I've read in a comic that was not very serious scientifically, but presented it as a fact, that one day, a beam of sound of 180 db was concentrated on Berlin's wall (concrete 1 meter thick), and it dug a hole in it !
The first inconsistency that comes to my mind is that Berlin's wall was made with stones. But this is worth checking. They also said that past 160 db, death was a possible issue for human beings.

Here is a waste of good helium. That gas is for breathing, underwater, of course. What exactly does this have to do with HA? Next we could discuss the sound weapons in the movie Dune. M'adib...boom!

Begin pure speculation:

The idea that atmospheric pressure puts a limit on the "loudest" possible sound "because you can't have lower pressure than a vacuum" doesn't make sense. This puts a limit on the negative half of the cycle, but the positive half of the pressure cycle can go as high as you want (theoretically, compressibility of air not withstanding).

If the negative part is clipped, but the positive part isn't, then the average pressure of the wave is relatively higher, hence you have (in a way) increased mean pressure.


Maybe there is a hard limit, and it's to do with what happens to air as you try to force it to the pressure required for that dB SPL?

(end of speculation!)

Cheers,
David.

The compression limit is thermonuclear fusion, but there might be some phase change before. I've just read that deep in Saturn, hydrogen was so compressed that it was in a metallic plasma state.

I didn't really think about there being a limit to sound pressure, but the limit to the expansion wave makes perfect sense. Nor can I find much information in textbooks about hypothetical sound pressure measurements at rocket exhausts.

When referring to the maximum sound pressure of air, keep in mind that the atmosphere an inch away from a saturn V rocket exhibits different properties than air, what it is composed of I'm not sure, aluminum, iron oxide, oxydizer... along with a large portion of unburn't liquid oxygen and water. How sound propogates through this... I dunno. But due to the vapour content, it's likely better than in air.

As far as the 190db sound hurting you, that would depend on frequency. If you have a low enough frequency wave eventually you get to a point where the wave is so long the pressure is static. This is how you can take enourmous pressure deep sea diving and survive...the rate at which you applied the pressure was extremely slow. It's rapid changes in pressure that do ear damage because you are unable to equalize you ear drum fast enough. Likewise, if the frequency is high enough (say 500,000 hz), 190db won't do any damage either because you ear cannot respond fast enough.

As for structural damage...a sound wave, even at 190db will have no effect whatsoever on most materials. Steel requires WAY more pressure than is available in a 190db sound wave to exceed it's yield strength. The way it can do damage is if the frequency of the sound is near the material's resonant frequency. This is where the object will begin to vibrate in sync with the soundwave. For example...the resonant frequency of my bedroom door is about 15Hz....if I have my subs playing a sine wave loud enough at that frequency, it shakes the hell out of it and if I could generate SPL loud enough at that frequency it could be damaged.

As for the rocket...the sound pressure from the space shuttle launch is actually great enough (and contains appropriate frequencies) that when it is ignited they need to dump 900,000 gallons per minute of water under the boosters to damp the vibrations and absorb energy. Else the tower would shake apart. Evaporating water is what is mostly responsible for the enourmous vapour cloud at launch. So I'd imagine it'd cause some inner ear discomfort

As for SPL limt...I'd assume the highest pressure a human has every created is during a thermonuclear bomb detonation. Fusion would make sense as being the limit...but then again it might not be. Subatomic physics is a bit beyond me.

The US government apparantly actually researched sound weapons...one of them generates a narrow sound wave around the resonant frequency of your bowels. I guess you can imagine what comes next.

Your tax dollars at work.

This is sorta true. It's hard imagining sound traveling around the world several times...you have to look at it as being a pressure wave, rather than a sound wave (sound implies a frequency range we can detect by ear). It'd have to be an enourmous amount of pressure (I'm thinking something like an asteroid impact...but it can happen). The comets that smashed into jupiter for instance created pressure waves which circled the planet for weeks. I could have sworn they had radio images or something of this on the discovery channel at one point. Krakatau likely did circle the earth a few times, but you need some really really sensitive instruments to detect it...nor was there any energy in frequencies in the audible range after a dozen or so kilometers. (think a lowpass effect)

A better way to visualize it is to look at weather images...there are areas of high and low air pressure that basically circle the globe. If you were to plot the pressure vs. time over a few weeks at any given location you'd get something that looks like a sound wave. The difference is that it will consist of extremely low frequencies (<0.0001 Hz). You can't classify it as sound since it is nowhere near our frequency threshold...but the mechanics are identical.