Hmm, OK......... 'Thick skinned' to me means you can 'hold your own' on AA's HE forum. The old alt.rec.audio crowd was the most abusive I've encountered. They banned me pretty quick for not being a 'yes man' to its high priests of audio. Regardless, I imagine V will fold like a cheap tent once Rtc gets a whiff of him.
GM
Scott, I hate you. John, you're a troll.
OK, with that out of the way... set up a tub of water. Get it sloshing back and forth at a resonant frequency. Now, while it's sloshing, stick a wire in it. Does that big ol' wave reflect off the wire?
Another example, near and dear to my heart, is the effect of particles in clear plastics. If they're really nano-scale, they hardly affect the transparency. Make them a couple of microns and the plastic is cloudy-to-opaque. Scattering (which is actually reflection) is strongly dependent on the scale of wavelength to scattering cross-section.
This is actually much easier to describe mathematically, but I suspect you'd rather have a physical picture.
OK, with that out of the way... set up a tub of water. Get it sloshing back and forth at a resonant frequency. Now, while it's sloshing, stick a wire in it. Does that big ol' wave reflect off the wire?
Another example, near and dear to my heart, is the effect of particles in clear plastics. If they're really nano-scale, they hardly affect the transparency. Make them a couple of microns and the plastic is cloudy-to-opaque. Scattering (which is actually reflection) is strongly dependent on the scale of wavelength to scattering cross-section.
This is actually much easier to describe mathematically, but I suspect you'd rather have a physical picture.
Thats easy enough
It follows the path exactly because it doesnt reflect
Pure logic 😀
In reality, I dont think low frequencies can bounce back at all
Thats the secret of whales communication over exstreme distances
Easier that what? Its not that easy to do mathemtically, it takes some pretty high level of math.
Scatering is not precisely reflection as diffraction is also an important characteristic. If it were only reflection then there wouldn't be any waves in the shadow zone, but there are. The full mathematical solution caculates both simultaneously.
To someone new here, it would seem that way, but I'm only too keenly aware of how hard it can be to grasp certain types of abstracts. My Waterloo is higher math. After 50+ yrs of periodically trying I've barely made any headway and I've had some pretty awesome teachers/math geniuses give it their best shot. Fortunately for me though, it hasn't kept me from getting a 'good enough' understanding of the physics of sound propagation that the math describes for those who can 'read' it since I can visualize it in other ways, so if my simplistic explanations seem too rhetorical to accept, just ignore them.
GM
Firstly, i respect everything you have done to help quantify TLdesign. I agree with the point. MOST of the energy is deflected around the bend, rather than being Reflected 180 upon itself. easiest route etc etc blah blah. that much is obvious.
one question though. along the line the lowest resonance doesnt notice the bends in a TL...but if a fold is introduced halfway along the length to accomodate the design, then we have 2 pipes of half the length. and the fundamental may see this as a single pipe, but any excitation around the octave higher will see the 2 sectional pipe resonances...SURELY
btw nice applet there Don...looks just like my washing machine and washing up bowl situation i mentioned earlier...its groovy
Last edited:
How about this?
There's an impulse - the cone moves and pressurizes the air. The opposite of "Nature abhors a vacuum" is she's not too fond of high pressure areas, either, and the dense air pressure wants to come to equilibrium so it expands outward. Not because it has momentum, but because the air molecules in front of it aren't pushing as hard as those behind it. When it reaches the turn, it pushes on the end, pushes on the side, and ends up pushing into the open space where, again, the air isn't pushing back.
A 20hz wave is a lot slower than the speed of sound, and there's no reflection because the whole 1/8th wave pipe back to the speaker is full of higher pressure. For a reflection to occur, the lower pressure of the leading edge of the wave would have to pressurize the denser air behind it which is busy expanding. Caught between the wall of the bend and the higher pressure coming down the pipe, it goes sideways.
Note that when a gas does have momentum, it's called "wind". 😉
In short... YES. But does it matter?
A thought experiment for you:
In a simple fold, the area of the line changes as you pass around the bend - it expands, then contracts, then expands again, then finally contracts to the area of the line after the bend. You can measure the effect this fold has on various frequency waves. You'll find, as have many others, that low frequencies - long wavelength relative to the pipe length) pass around the fold with very little loss or reflection. High frequencies - short wavelengths - reflect strongly from the fold.
Now imagine straightening the bend back to a straight line, but keep the area changes - in other words, an expansion-contraction-expansion-contraction of the line. Now measure the effects on the various frequencies again. Surprise, surprise, surprise...
"Aha", you say, "I could add curved "fillets" to my folds to ensure they have a constant area around the bend." Well, yes, you could, if you need your line to function well at higher frequencies. It's just that for most applications of transmission lines and tapped horns etc, efficient transmission of higher frequencies is undesirable. They are to be suppressed, not transmitted.
So getting back to your original point, the resonances of the two pipe sections are (hopefully) above the designed operating range of the system. There is some logic in having more folds in a line rather than fewer, since the resulting higher order resonances are at higher frequencies which (a) will hopefully not be present in the first place due to the speaker crossover, and (b) are more easily damped by lining or stuffing, which becomes more effective as the frequency increases.
Sorry, you lost me there. Could you perhaps clarify it for me?
Sound travels at the speed of sound. That's why it's called that.
Although not a popular position, I completely agree. You don;t really understand something until you can model it. Otherwise your just guessing.
Regarding the fixed Wikipedia entry on transmission lines, I'd suggest this isn't the first time it has happened. Look at the reference to the Kappellmeister speaker and then have a look at
S.U.H.T.L.
or the modestly named
Resolution
and you'll see it's been done before. I think it is time someone who knows the subject posts some information on that page.
S.U.H.T.L.
or the modestly named
Resolution
and you'll see it's been done before. I think it is time someone who knows the subject posts some information on that page.
Easier than describing a spiral staircase without using your hands. 😀 Like you and jlsem, I find it easier to deal with the math- it's really not that high a level, just basic differential equations- than to try to do it through physical analogy. My favorite treatment was French's "Vibration and Waves," from the excellent MIT introductory physics series which I used as a freshman, but there's plenty of others.
I was trying to express the idea that the wave is going around the corner in slow motion, so to speak. On reflection, (pardon the pun) I suppose it has more to do with the size of the pipe than the speed of sound, but the important concept is that the front edge of the wave is reaching the corner while the speaker is still compressing the air.
When someone has trouble visualizing a wave turning a corner in a pipe, it occurs to me they may have two difficulties. They may be thinking that all the air in the pipe is of equal pressure, and they may be thinking that the wavefront has momentum that needs to be accounted for. (the wave may, indeed, have some momentum, but I suspect that it's negligible) My explanation isn't meant to be rigorous, merely easier to grasp than Martin's whipped cream.
There still isn't a clear understanding of gravity - seriously, so calling it "complicated" is an understatement. I'm sure that when it is finally fully understood it can be explain concisely, without unnecessary rhetoric.
The portion of the wave that contacts the wire you mean? I know that big ol' wave is reflecting off the side of the tub...that being my point in all of this. You gentlemen would deny that aspect of the scenario.
I'm big on visualization and adding a border to that java applet shows the reflection I'm talking about.
More from the peanut gallery? 🙂
I'm actually doing just fine grasping the concepts - I've posed some fairly interesting questions and still those of you who (supposedly) have a better understanding and grasp on the "abstracts" have failed to provide a logical answer.
Last edited:
How about this: Accept the logical conclusion that the wave reflects from the sidewall. It's simple, neat and uncomplicated - it can't be questioned: the phenomenon can be demonstrated out here in the real physical world (the woofer 10 inches from the concrete wall example). It explains so much.
Do it, give in to the dark side!
No, not so much, really. It IS reflecting off the ends, but you don't see any real reflection from the sides, just the expected drag flow. You can get a nice, straight wave in a tank on a rocker.
I'm not a gifted math guy at all, but maybe the whip cream analogy is hard to visualize because it has lots of mass? Thick, creamy ,sticky mass..
How about you force thick smoke down a straight line, like say in a unfolded BIB, it should just pass through like in a chimney.. Now fold that exact same cab in half keeping all else equal as is done in most BIB's.. Force the thick smoke down the line and measure what happens.. I would think at least with smoke, that there would be some turbulence and back eddy's or pressure at or somewhere near the fold or bend etc?
🙂
How about you force thick smoke down a straight line, like say in a unfolded BIB, it should just pass through like in a chimney.. Now fold that exact same cab in half keeping all else equal as is done in most BIB's.. Force the thick smoke down the line and measure what happens.. I would think at least with smoke, that there would be some turbulence and back eddy's or pressure at or somewhere near the fold or bend etc?
🙂
- Status
- Not open for further replies.