Why Does Sound Propagate?

[crashsite]

A bit of the "process"

Why ....... ?

That's an excellent question and, believe it or not, one that I've really had to wrestle with. For example, as I sit at my computer and my alarm goes off (a rather high pitched beeping), I can move my head around a bit and hear peaks and nulls in the sound. How can it do that if there's not at least standing waves present? How can it do that if it's not putting different pressures on my eardrums?

Something like this usually comes to me as a series of "aha" moments. Junctures where some aspect suddenly "clicks". This was no exception.

User, notauser mentioned that the molecules vibrated at gigahertz rates. I mentally stored that bit of info. Later someone posted a link with a little animation of air molecules and the caption said it was slowed down 2 trillion times. "Eureka"! Now I had a sense that the molecular collisions were at a picosecond time scale.

Then, someone posted one of those "ask a scientist" links and, on that page was the formula for computing the speed of air molecules. What's more, the answer was in range of the speed of sound (about 1100 mph). What's more, the only thing in the formula that allowed the speed to change was temperature. "Eureka"! That's when I realized that the speed of sound depended directly on the speed of the molecules and that speed depended on the temperature.

That's when it started falling into place that the sound propagated by those picosecond time frame collisions with molecules traveling at 1100 mph. But, how did that relate to the speed of sound. I didn't know because I didn't know how the sound got impressed onto the molecules.

Then, I deduced that it was all just a timing issue (with my "famous" colored molecule post on the bottom of page 41). That post spells out how the "sound" gets encoded onto the molecules and then gets propagated as a molecular displacement.

There is no pressure and there is no wave when the action is the timing of when 1100 mph molecules strike the disturber. But, you do need to accept that motion of the molecular movement continues to be 1100 mph and essentially random but, with some of them carrying a tiny positional bias.

A fair analogy is that the signals from the GPS satellite constellation are pretty weak. In fact, as received on Earth, they are below the noise floor. But, by statistical iteration, the signals can be coaxed out of the noise and made useable. That takes time and is the main reason it takes awhile to get a GPS fix.

A similar thing happens with sound. The picosecond interactions between the disturber and the medium still appear to be random but, over time, can be integrated at the receiver to extract the audio signal.

None of that requires a longitudinal or traverse pressure wave. Sorry, but it just doesn't.

 

[Sceadwian]

Crash, you have 711 posts, I think better than half of them are in this thread, and you have as yet to come to any kind of a point, other than attempting to prove a common viewpoint wrong on a technicality which isn't even a theory because you've posted no testable conditions under which there is any way to distinguish your viewpoint from established theory other than using different language.

Your posts are bordering on obsessive compulsive.

 

[crashsite]

Damnit! You've made me editorialize again....

...which isn't even a theory because you've posted no testable conditions under which there is any way to distinguish your viewpoint from established theory other than using different language.

Your posts are bordering on obsessive compulsive.

I'll take the first part first:

I was thinking about this exact thing just today. First of all, it is a theory. Any idea, crackpot or not, can be a theory but, to become more than just a theory it needs to be proven. This is a tough one and, I believe, one of the reasons the prevailing view persists. My theory is essentially "untestable".

The notion is that the sound is propagated by statistical displacements of the molecules. But, the instant you put some sort of receiver into the environmnet, you distort the experiment and pollute the result. The mere fact that you make the measurement means that you've converted some of the molecular displacement into a pressure. What seems to be the result is what must have been a pressure wave all along. Furthermore, wherever you go in the sound field and make the measurment, you see the pressure and, as you move around in a sound field that has reflections, you can measure standing waves (which sure do look and feel real).

But, just because you've skewed the environment by making the measurements doesn't invalidate the theory.

While you can't directly test the theory, there are numerous indirect ways that you can both test my theory and test the prevailing theory as well. I noted a couple of them in my last post to user, 3v0. Part of the testing is just seeing if it makes sense based on observed results. Does it make sense, for example, to assume that a speaker cone that's moving and pushing air around at about 1 mph, is going to suddenly be pushing a sonic shock wave along at 770 mph by the process of one molecule pushing on the next? See...it makes no sense at all. So, why not look for something that does?

On to part two:

Trust me, OCD is not one of my characteristics. I suppose we all have some traits that some other person might ascribe to OCD. Probably most (if not all) of us here would be considered computer junkies with OCD personalities about it...at least by people who don't really use computers or only use them minimally like at work or to do e-mails.

But, I don't like leaving problems hanging when I feel like I am still making progress on figuring them out. I've noticed that the folks on the internet don't have much attention span about stuff and tend to write in little more than monosylabic grunts. Our current US President was voted in with a one-word campaign slogan..."change". Josef Goebels understood this and used it very effectively and, that was back in the day when people prided themselves on being smarter and more industrious (just the way the twitter/tweet dweebs of today will remember themselves in another 40 or 50 years).

The people in this forum are usually better but, still don't like much "in depth" and "back to basic" thinking about things. There are a lot of PIC "experts" here but, for some reason you can't get any usefule information out of them. The few that actually are experts tend to turn up their noses at silly questions by neophytes and the other "experts" have nothing useful to offer at all.

You see. I've looked at the spec for a couple of popular PICs and I have some things I'd like to do with them. But, I don't want to program in C++ and then use some program to compile it to the PIC. I see it as a piece of hardware. If it's a simple application, I want to just program the routine in hex and binary, burn it into some onboard ROM, and be done with it. The help for doing that is non-existant. Both the true and phony experts sneer at such mundane endeavors.

 

[Nigel Goodwin]

You see. I've looked at the spec for a couple of popular PICs and I have some things I'd like to do with them. But, I don't want to program in C++ and then use some program to compile it to the PIC. I see it as a piece of hardware. If it's a simple application, I want to just program the routine in hex and binary, burn it into some onboard ROM, and be done with it. The help for doing that is non-existant. Both the true and phony experts sneer at such mundane endeavors.

You seem to live in a different world to the rest of us?.

There's nothing on here about programming in C++ (it's not a PIC language, it's a PC one).

The vast majority of PIC programming, and advice on here, is in assembler.

You certainly won't get advise on hand assembly (only a complete idiot would do it, when free assemblers are available) - but there's huge amounts of help here for assembly programming on PIC's.

If you did want to hand assemble? (and you often had to 30+ years back), everything you need to know is in the datasheets.

 

[Pommie]

I have only read the last two pages. This is complete nonsense but I will keep reading. This is like a soap where they spout absolute garbage but you have to keep watching/reading. I know the guy will eventually be shot down in flames (already has) but I'll look in now and again just to make sure he hasn't been abducted.

Mike.

 

[Nigel Goodwin]

I have only read the last two pages. This is complete nonsense but I will keep reading. This is like a soap where they spout absolute garbage but you have to keep watching/reading. I know the guy will eventually be shot down in flames (already has) but I'll look in now and again just to make sure he hasn't been abducted.

I'm still in two minds as to lock the thread, delete the thread, or keep ignoring it - it's the biggest load of rubbish on here so far.

 

[Pommie]

I'm still in two minds as to lock the thread, delete the thread, or keep ignoring it - it's the biggest load of rubbish on here so far.

Give it another day or two, if he's not been abducted by then, then make your decision. (Two thens in a row and it made sense).

Said in the best Holly voice (Red Dwarf), "you have to laugh".

Mike.

What about 5 ANDs in a row? I know a sentence with 5 consecutive ANDs that makes sense.

 

[crashsite]

Meaningful dialog...but, with a chip?

You seem to live in a different world to the rest of us?.

I surely do seem to live in a different world than programmers.

There's nothing on here about programming in C++ (it's not a PIC language, it's a PC one).

The vast majority of PIC programming, and advice on here, is in assembler.

You certainly won't get advise on hand assembly (only a complete idiot would do it, when free assemblers are available) - but there's huge amounts of help here for assembly programming on PIC's.

If you did want to hand assemble? (and you often had to 30+ years back), everything you need to know is in the datasheets.

Yes, I was making an extreme example of it...but, it's still the "programmer's mentality"...a different world. I would generally prefer to design electronics to do something rather than trying to talk it into doing it.

This is the wrong place to mention this but, I'm kind of loathe to try to put something so 'conceptural' into the, Microcontroller Forum. I've been thinking about a controller for the damper on my wood stove. I've been thinking about discrete logic (one-bit sensing of temp and a bi-directional stepper motor sequencer...and a one bit alarm line). It's one of those things that's just a bit more complex than I really want to do discretely but, not sure if I want to face the programmer crowd to try to describe it and then sift through the 'programming'. It seems like a likely candidate for PIC hand programming.

 

[crashsite]

UFOs

...but I'll look in now and again just to make sure he hasn't been abducted.

I wont be abducted. I'm wearing tin foil on my head.

What can I say. Genius is never appreciated in its time.

 

[crashsite]

The Saga Continues

I'm still in two minds as to lock the thread, delete the thread, or keep ignoring it - it's the biggest load of rubbish on here so far.

Well, whatever you decide to do is beyond my control. I think the time will come when this view of sound propagation will be the accepted one and I'll have a, time-stamped record of what I've said.

I'll give fair warning that there is more to say and I plan to say it...unless you lock it out (I'm not sure why you'd want to but, I must say that I'm not sure why most people do what they do in this world). If you delete it, I suppose I wont even have the record.

Perhaps it at least has redeeming social value, if only in it's ability to entertain folks like user, Pommie?

 

[crashsite]

An Experiment - The Bass Reflex Speaker Cabinet

Xxxxxxxxxx

 

[Nigel Goodwin]

Because the speaker cone is pushing an air mass around, that foot or so is the path length needed to take that air to the back side of the speaker with the correct timing to dampen the resonance. That process is a pressure process. It can have audio qualities...but, it's just not sound propagation (at Mach 1).

That's not what ports do, or how they work - nothing to do with dampeming the resonance (where an infinite baffle enclosure does it better).

 

[crashsite]

Sorry guys...

That's not what ports do, or how they work - nothing to do with dampeming the resonance (where an infinite baffle enclosure does it better).

You're right, of course. I've deleted the content of that post pending further research. I was thinking of something else regarding the speaker mechanical resonance.

The gist of your comment is in perspective from the quote you made.

 

[Sceadwian]

I'm strongly leaning towards locking the thread... Reason has left the building, and I'm subscribed, so I see every post now =)

 

[crashsite]

"Subscriptions"

I'm strongly leaning towards locking the thread... Reason has left the building, and I'm subscribed, so I see every post now =)

You'll only get notifications if someone quotes you. If you request, I wont and, if you don't make replies or comments, there's no reason anybody else will either. You only got back into the loop because you jumped in to comment that you didn't like the thread. In fact, no reply here will be interpreted as a tacit request to discontinue participation. It's not a ploy to exclude you. You're also welcome to continue to participate at any time...if you want to.

I think it's common courtesy to at least respond if someone takes the time and effort to participate...if only to gripe. So, note to all: No posts, no replies = no notifications. I don't go outside the thread to solicit participation from individual users and any quotes I make, going back into the archives of the thread, don't carry the user's signature (that's reserved for direct and immediate replies).

 

[crashsite]

Start with an extreme example...

Let's take an extreme example and then see if maybe working backward from there might shed some light on the processes involved.

If you blow a puff of air at a spider web several feet away, there is a fair amount of time for that puff to reach and move the web. Then you blow the puff you also mke a sound...a whoosh sound.

The air puff travels slowly and, in fact, it's pretty easy to show that it slows rapidly as it moves outward and diffuses. If you line up some small candles between your mouth and the web, you can see the flame flicker as the air puff passes by them. It's easy to do and very graphic.

The "whoosh" acts different. It takes off at the speed of sound (Mach 1) and doesn't slow down. In the few seconds it might take for the air puff to reach the spider web, the whoosh sound (if it can still be heard) is already a couple of thousand feet away.

If a speaker cone is pulsed similar to the way the diaphragm under the lungs is when making an air puff, it will push out a "puff" of air, too (in the compression direction). Whether the puff is generated by lungs or the speaker, it acts similarly. Likewise, the click sound that the speaker will make when pulsed will propagate at the speed of sound, just like the whoosh did.

I've never seen this experiment done but, it would be interesting. If you drive a speaker with some waveform, such as a sine wave, the speaker cone both moves air and propagates sound. If the sine wave is causing the cone to vibrate in the audible frequency range, that moving air can also create an auditory sensation (sound).

Very close to the speaker, where the air is being moved, there are two sources of the sound. One is the moving air (at or near speaker cone speed). The other is the propagated sound (at Mach 1). Since the audio signal is being produced by two different mechanisms and at two different speeds, there should be two signals in the air space.

Detecting them should be possible but, probably not easy. For one thing, the air motion is very short range (especially as the frequencies get high enough to be audible). For another, the sound is generated across the area of the cone so there are automatically multiple paths to consider. For another, it's not possible to determine if the pressure that's moving some sort of receiver (such as a microphone) is from the air movement or from the molecular displacements being converted back into pressures...they look alike at that juncture.

But, by looking at the extreme example and mentally working back toward the case of the speaker, it's not just possible but, practical to consider that there are two signals present.

 

[Sceadwian]

Crashsite. I do an 'advanced search' for any active threads that I have ever posted in, that's why I was so surprised when this one showed activity still. Generally if a thread shows up there it is of either some personal, or technical merit, at this juncture it is wondering why the same dead horse is still being beat.

Molecular displacement and pressure ARE THE SAME THING. You're talking in circles and it makes absolutely no sense at all..

I'm going to re-iterate an explanation of the reason for sound to propogate one more time.

Physical structures acquire energy which is translated into a movement relative to it's surrounding environment. Said physical structures do not have to be the same type of molecule, and in practice never can be as every real world object is in fact a hodgepodge of trace atoms with a primary atom type on the best of days. So right from the start making any sense of it all on a fine scale goes right out the window because of all the distortion related to the physical materials themselves.

When viewed from a distance electricity is nothing more than a type of 'sound' except instead of the whole molecule moving only the electrons have to fly around.

I'm not sure why you could possible consider pressure and 'molecular displacement' separate things. You're quiet simply not making any sense at all.

 

[crashsite]

What's the worst is that I really dislike statistics...

...at this juncture it is wondering why the same dead horse is still being beat.

I don't believe the horse is dead.

Molecular displacement and pressure ARE THE SAME THING. You're talking in circles and it makes absolutely no sense at all..

Empirically, it sure seems like they should be. In fact, it's one of the things that had me confused for quite a long time. I resolved it with this logic:

Consider a static environment (one in which the molecules are essentially at rest unless they are being moved by some directed force...or where you are thinking of a large enough population of molecules to consider the population to be stationary...unless moved by a directed force). In that case, what you are saying is true.

A force pushes the molecules and they bunch up, creating a higher pressure region. In fact, having more molecules per unit space is pretty much the difinition of higher pressure. When considering pushing around an air mass, that's pretty logical thinking and it's easy to back that thinking up experimentally.

When thinking about the molecules, it's not so clear cut. The molecules cannot be thought of as being stationary. They are, in fact, zipping around at some 1100 mph (in air, under standard conditions and moving or vibrating at other speeds in other materials) and in random directions. The reason they are doing that is because they are absorbing heat. Any analysis of the action at the molecular level must take that motion into account.

Because of the random nature of the movement of the molecules, you cannot specify a future position for them to be (even using the most powerful math...there's just too many of them and they are changing position too fast). But, even though you can't define any pattern to the positioning of the molecules, you can statistically predict how and where the result will show up.

It's not done so much in science but, people who develop things like actuary tables for the insurance industry do it all the time. They have no idea which individuals will get sick or die but, given a large enough population, they can pretty accurately predict how many and generally where it will happen. It's the same sort of thinking that needs to be applied to sound. The reason: Because of the random nature of the movement of the molecules.

Physical structures acquire energy which is translated into a movement relative to it's surrounding environment. Said physical structures do not have to be the same type of molecule, and in practice never can be as every real world object is in fact a hodgepodge of trace atoms with a primary atom type on the best of days. So right from the start making any sense of it all on a fine scale goes right out the window because of all the distortion related to the physical materials themselves.

It's expected that materials will be a mish-mash of molecules. Air is definitely a mixture of gasses (both elemental and compound). That's a factor that I have...suspicions...about but, can't prove. I believe that, as sound propagates through air, it not only propagates at a wide variety of speeds (between 0 and 1100 mph (in air), averaging about 770 mph), but, depending on which gas molecules are involved, may often travel even faster than 1100 mph, like when a helium atom happens to be involved. I haven't tried to address this sort of thing in detail becuase I just don't have even a good theory to back it up. Like I say, there's still life in that horse.

When viewed from a distance electricity is nothing more than a type of 'sound' except instead of the whole molecule moving only the electrons have to fly around.

I agree. As we know, electrons (as a mass) move very slowly through a wire but the effect moves very fast. Very similar to the situation with sound. But, how fast do the electrons themselves actually move. Going back into my memory banks, I recall that it's at x-ray frequencies (those short wavelengths define the resolving power of something like the electron microscope). I've got a really neat book around here of papers that were written in about the 1930s about the research that was being done about this stuff. It would be hell to find but, if I run across it, I'll post the title and particulars. It was written in a surprisingly readable style for that sort of material.

I'm not sure why you could possible consider pressure and 'molecular displacement' separate things. You're quiet simply not making any sense at all.

As noted above, it only starts to make sense when you consider it as a statistical problem.

 

[crashsite]

"Non-mathematical" Math

Just for fun, I thought I'd try putting the concepts of the previous post into a sort of a "non-mathematical" math.

When defining the random motion of the molecules, even if you know their starting positions (all 'zillion' of them), once they start moving around and colliding, there's no way to keep track of them individually.

What we do know is that, at any given instant, each molecule will have some position somewhere in the universe. It's a 3-D universe so, the coordinates can be defined by X, Y and Z. We just don't know and can't predict where X, Y or Z are or are going to be so we can't put a numerical value on them.

If we impress a known bias onto that position, we still don't know the molecule's position but, we do know that it's whatever it's position would have been, offset by the amount of the bias. If the offset is +1 in the X axis, then the position will be 1+X but, since X is not known, we can't put a numerical value on 1+X.

If we follow that bias from molecular collision to collision, it continues to influence any molecules that are involved with the molecule that experienced the original offset. It's a timing issue.

In the case of an air disturber, once the offset has been put onto the molecules by movement of the disturber, it propagates. It propagates by virtue of the fact that the timing (and, thus the spacial positioning) of the molecules, has changed.

The energy to propagate that effect is contained in the molecules themselves. That energy is the heat energy that's making the molecules move in the first place. That's the way it has to be. No other explanation can be made to make sense.

Even though we don't know the position of any molecule, we do know that a true random distribution of them yields a vector sum of all their movements of zero (or very, very close to it). When there is a bias applied to the molecules, at the receiver, the randomness of the molecules still averages out to zero...but, the offset doesn't.

I'll leave it there for the time being...

 

[smanches]

The only energy needed to propagate a wave is from the disturbance itself. The inherent energy of the molecules has nothing to do with it. There is no energy lost/consumed when molecules collide (unless it's a very powerful collision which changes the molecule itself and releases the energy that was holding it together.)

I also wonder why you are trying to re-prove/dis-prove something that 1000's of people, who actually do the math, have proven time and time again.

This thread is like a bad wreck. I just have to see if anyone is still alive in the end.