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Author Topic: Importance of basic understanding & fundamentals  (Read 2066 times)

Ed Hall

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Re: Importance of basic understanding & fundamentals
« Reply #20 on: April 20, 2017, 11:04:59 am »

The problem in teaching or explaining sound is that it's invisible, but no amount of visualization is likely to create an "ah ha!" moment that can't be done already.

The Ah-Ha! Moment for me happened in high school physics class. We were shown a movie (before video was everywhere) about sound waves. I understood the cyclic nature but always thought of a sign wave. The movie showed parallel lines moving closer together and further apart. Compression and rarefaction. Then it showed similar but using concentric circles. That was the moment! Since then I've seen sound in my head like the concentric circles, or partial circles-arcs.

Judging from the production quality, spliced film and cheap school I would assume the film was from the 60s. But it worked because the fundamentals don't change.
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John Roberts {JR}

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Re: Importance of basic understanding & fundamentals
« Reply #21 on: April 20, 2017, 12:05:58 pm »

another (very old) way to visibly demonstrate standing waves is the old sand on a flat metal plate that is vibrated by a speaker (or violin bow). The sand will aggregate over nodes and be pushed away from anti-nodes. Again only 2 dimensions but a square or rectangular metal plate is closer to a room shape than a mud puddle.

JR 
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Chris Hindle

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Re: Importance of basic understanding & fundamentals
« Reply #22 on: April 20, 2017, 12:50:24 pm »

another (very old) way to visibly demonstrate standing waves is the old sand on a flat metal plate that is vibrated by a speaker (or violin bow). The sand will aggregate over nodes and be pushed away from anti-nodes. Again only 2 dimensions but a square or rectangular metal plate is closer to a room shape than a mud puddle.

JR
I dunno JR, I've been in some pretty ugly rooms.....
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Tom Danley

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Re: Importance of basic understanding & fundamentals
« Reply #23 on: May 13, 2017, 09:55:51 am »

The Ah-Ha! Moment for me happened in high school physics class. We were shown a movie (before video was everywhere) about sound waves. I understood the cyclic nature but always thought of a sign wave. The movie showed parallel lines moving closer together and further apart. Compression and rarefaction. Then it showed similar but using concentric circles. That was the moment! Since then I've seen sound in my head like the concentric circles, or partial circles-arcs.

Judging from the production quality, spliced film and cheap school I would assume the film was from the 60s. But it worked because the fundamentals don't change.


 Hi Ed
A  clear mental image of how sound behaves in a given circumstance can be very useful.  I love this stuff, maybe I can add some more to it.
The picture of bunched up and stretched apart lines representing local areas of increased and decreased pressure is a good one but there is another part which can be added to make a more complete image.
Take radio waves as an analogue, one can pick up radio signals two ways, one you use a ¼ wave length or other antenna which picks up the Voltage component of the radio wave OR one can make a loop coil antenna which uses the magnetic portion of the wave to induce a voltage in the loop.  The voltage and magnetic potentials are both since waves BUT they are shifted 90 degrees with respect to each other, in quadrature and where the magnetic potential is greatest, the Voltage potential is Zero and vis versa..
With sound there is a similarity although entirely different mechanisms.  With air, we have about 80 miles of it piled up above us and down here, the “weight” of all that is about 15 pounds per square inch. Thankfully we know nothing else and are sensitive to VERY small changes in pressure within a certain rates of change.  If you represented the pressure of a sound wave as a sine wave, going both above and below ambient air pressure, one has the density part of the sound wave, the pressure and THAT is what we hear, changes in pressure.
Part B is that shifted 90 degrees to that pressure sine curve is the Velocity one see if they followed a given air molecule.  In the animations, one can see the motion is zero when the lines or particles are both closest and farthest apart.   So sound is really two things in quadrature, potential and kinetic energy.
The velocity part of sound “we” don’t think that much about unless you design horns scientifically although there are examples of “velocity devices” such as a velocity microphone.  Where a “normal” condenser or dynamic mic is a pressure transducer, a velocity mic has a VERY light casually suspended conductor in an magnetic field. It is so light, it is swept along by the air molecules and the voltage it generates tied more to velocity and not pressure.
I could ramble on about sound but I won’t, instead for those still reading, I will pose a thought experiment or question.
Starting at DC and going up in frequency we call that part of the electromagnetic radio “radio waves” and all of these are the same in that they are that voltage and magnetic potential in quadrature arrangement.  As you go higher and higher up in frequency and shorter and shorter in wavelength, high MHz / low GHZ, radio waves travel through copper tubes and plumbing, at high GHz radio components look a lot like optical components but “somewhere” we cross into light.   
With light, we talk photons and the odd fact that experiments show light behaves like both a particle and a wave.   Is the fact that light demonstrates itself to be a wave evidence that it is also a voltage and magnetic potential in quadrature but that “we” are unable to resolve the difference at that scale and use the term photon instead to describe a short (perhaps minimum quantity that can be radiated) envelope of em energy.
Ok, so while am cleaning out the accumulated “spinach” and fire ant mulch under the deck and sharpening the blades on the lawn tractor, give that some thought.  Grass grows fast in the spring in Georgia!
Best,
Tom
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John Roberts {JR}

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Re: Importance of basic understanding & fundamentals
« Reply #24 on: May 13, 2017, 11:19:25 am »

Grass and fire ants grow fast in MS too....  lots of symmetry to be found if we look under the right rocks...

JR
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Ivan Beaver

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Re: Importance of basic understanding & fundamentals
« Reply #25 on: May 13, 2017, 11:30:40 am »

Grass and fire ants grow fast in MS too....  lots of symmetry to be found if we look under the right rocks...

JR
But up at Toms place-sometimes the right rock can have gold (literally) under it. :)

There is a theory that the ancient Myan city of gold was actually up near Dahlongia Ga.  They have found Myan ruins in the area, and the first gold rush in the US was there.
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John Roberts {JR}

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Re: Importance of basic understanding & fundamentals
« Reply #26 on: May 13, 2017, 02:04:29 pm »

But up at Toms place-sometimes the right rock can have gold (literally) under it. :)

There is a theory that the ancient Myan city of gold was actually up near Dahlongia Ga.  They have found Myan ruins in the area, and the first gold rush in the US was there.

Are you sure his name isn't Tom Sawyer and that is a ruse to get gold crazed prospectors to pick up his rocks?

JR
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Ivan Beaver

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Re: Importance of basic understanding & fundamentals
« Reply #27 on: May 13, 2017, 03:03:17 pm »

Are you sure his name isn't Tom Sawyer and that is a ruse to get gold crazed prospectors to pick up his rocks?

JR
Actually he is playing around with an idea to use sound to extract the gold dust in decent quantities.

There is lots of dust around, it could all add up ;)
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John Roberts {JR}

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Re: Importance of basic understanding & fundamentals
« Reply #28 on: May 13, 2017, 03:25:48 pm »

Actually he is playing around with an idea to use sound to extract the gold dust in decent quantities.

There is lots of dust around, it could all add up ;)
Big dog miners used water to separate it out, as the heavier gold would precipitate out... Sound might work but seems like a mess... and loud.

JR
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Ivan Beaver

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Re: Importance of basic understanding & fundamentals
« Reply #29 on: May 13, 2017, 03:30:30 pm »

Big dog miners used water to separate it out, as the heavier gold would precipitate out... Sound might work but seems like a mess... and loud.

JR
And fun
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Ivan Beaver
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