markovchain17
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Hi TSR, I've been recreationally studying sound synthesis theory and have come across a section that is explaining how acoustic sound is converted into variations in voltage. An example is a microphone picking up sound from a voice and converts it into variations of voltage. I don't have the best knowledge of physics and have forgotten a lot of it from GCSE but my problem is I don't quite understand the 'variations of voltage' as I don't really understand what voltage is. I think it's referring to the graphs like these:
Image

But I thought these graphs show variation of amplitude, not voltage? Also I don't get quite how you get -1 amplitude so maybe I don't know what amplitude is either

Could someone help clear up these things for me please?
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markovchain17
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Joinedup
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(Original post by eternaforest)
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Here's an explanation of the amplitude of waves http://www.bbc.co.uk/schools/gcsebit...avesrev3.shtml

sound is a pressure wave in air
voltage is sort of like electrical pressure
a microphone converts the changes in air pressure to changes in voltage... which is useful because we can make amplifiers, recording systems etc that work electronically.
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markovchain17
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(Original post by Joinedup)
Here's an explanation of the amplitude of waves http://www.bbc.co.uk/schools/gcsebit...avesrev3.shtml

sound is a pressure wave in air
voltage is sort of like electrical pressure
a microphone converts the changes in air pressure to changes in voltage... which is useful because we can make amplifiers, recording systems etc that work electronically.
So amplitude is the maximum amount of disturbance from the waves undisturbed position? What's the undisturbed position? And I still don't get how you have negative amplitude
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Kyx
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eternaforest

Alternating voltage:http://www3.nd.edu/~lemmon/courses/e...b8b/node4.html

Since sound is a type of wave, it can be converted into alternating voltage. If it wasn't a wave, just a straight line, it would be direct voltage.
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markovchain17
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(Original post by Kyx)
eternaforest

Alternating voltage:http://www3.nd.edu/~lemmon/courses/e...b8b/node4.html

Since sound is a type of wave, it can be converted into alternating voltage. If it wasn't a wave, just a straight line, it would be direct voltage.
Ah that is interesting, I remember doing the electromagnetic stuff in GCSE. So in the context of sound, when converting the sound (fluctuations in air pressure) to analog, the varying voltage is analogous to the fluctuating air pressure?
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uberteknik
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(Original post by eternaforest)
Ah that is interesting, I remember doing the electromagnetic stuff in GCSE. So in the context of sound, when converting the sound (fluctuations in air pressure) to analog, the varying voltage is analogous to the fluctuating air pressure?
Not just analogous, it's a facsimile of the sound pressure.

Electric Charge is a fundamental property of electrons (and protons). It's a force measured in Coulombs as a very small amount carried by every single charged particle. Grouped together, collective charge can exert an enormous force against other charges.

Electric Current is the movement of electrons (hence charge) within a conductor. i.e. the rate at which electrons flow.

Voltage is a measure of the 'potential' for electrons to do work. Recall that all like charges repel each other. So if electrons are caused to bunch together by an external force, they will exert an equal and opposite force (Newton's law of action and reaction) trying to push back. That is, they will create an electron 'pressure' force which is measured in volts.

i.e. voltage potential = joules per Coulomb of charge.

Sound causes the microphone diaphragm to move in sympathy with the air pressure wave hitting it. The diaphragm is coupled to a coil which moves within a static magnetic field and generates an alternating current as a result:

Compression causes the diaphragm to move in one direction which generates an electric current moving in one direction. Rarefactions cause the diaphragm to return to (or overshoot) it's rest position and hence electric current is also generated and moves in the opposite direction.

In this way, pressure compression and rarefaction causes the diaphragm and hence electromagnet assembly to move in sympathy and generates an alternating electric current accordingly.

The voltage amplitude is a measure of how efficiently the microphone converts the air pressure energy into electron pressure potential energy.
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markovchain17
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(Original post by uberteknik)
Not just analogous, it's a facsimile of the sound pressure.

Sound causes the microphone diaphragm to move in sympathy with the pressure wave hitting it. The diaphragm is coupled to a coil which moves within a static magnetic field and generates an alternating current as a result:

Compression causes the diaphragm to move in one direction which generates an electric current moving in one direction. Rarefactions cause the diaphragm to return to (or overshoot) it's rest position and hence electric current is also generated and moves in the opposite direction.

In this way, pressure compression and rarefaction causes the diaphragm and hence electromagnet assembly to move in sympathy and generates an alternating electric current accordingly.
This was very helpful, thanks So in microphones there's a diaphragm... I wouldn't have guessed. So the peaks are the compressions and the rarefactions are the troughs? What would the halfway point be i.e. at 0, would that be a sort of balance of the two?
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uberteknik
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(Original post by eternaforest)
So the peaks are the compressions and the rarefactions are the troughs? What would the halfway point be i.e. at 0, would that be a sort of balance of the two?
Exactly. I've edited my original post which should make a bit more sense.

0V is the rest position with equal pressure on both sides of the diaphragm.

No movement = no voltage pressure.
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markovchain17
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(Original post by uberteknik)
Exactly. I've edited my original post which should make a bit more sense.

0V is the rest position with equal pressure on both sides of the diaphragm.

No movement = no voltage pressure.
It makes a whole lot more sense to me now! Thank you
So amplitude is only describing the height of the peak, but it's measured in volts since the type of wave is dealing with electric currents? I'm trying to say basically that what the amplitude is measured in is dependent on what type the wave is?
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uberteknik
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(Original post by eternaforest)
It makes a whole lot more sense to me now! Thank you
So amplitude is only describing the height of the peak, but it's measured in volts since the type of wave is dealing with electric currents? I'm trying to say basically that what the amplitude is measured in is dependent on what type the wave is?
Yes, amplitude in this case is interpreted in three ways depending on the labelling of the graph axes:

Amplitude is a measure of the maximum and minimum air pressure arriving at the diaphragm. i.e. pressure vs time.

Amplitude is also a measure of the displacement of the diaphragm in motion terms. i.e. distance from the rest position vs time.

Amplitude is also a measure of the potential voltage pressure generated by the electro-magnet assembly. i.e. volts vs time.
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markovchain17
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(Original post by uberteknik)
Yes, amplitude in this case is interpreted in three ways depending on the labelling of the graph axes:

Amplitude is a measure of the maximum and minimum air pressure arriving at the diaphragm. i.e. pressure vs time.

Amplitude is also a measure of the displacement of the diaphragm in motion terms. i.e. distance from the rest position vs time.

Amplitude is also a measure of the potential voltage pressure generated by the electro-magnet assembly. i.e. volts vs time.
Makes perfect sense Do you know a lot about sound synthesis, or just physics in general?
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uberteknik
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(Original post by eternaforest)
Makes perfect sense Do you know a lot about sound synthesis, or just physics in general?
Both

My first love is music which went hand-in-hand with the engineering of sound reproduction which in turn lead me into electronics engineering and then aerospace!

But I never lost my roots and am still into sound engineering.
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markovchain17
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(Original post by uberteknik)
Both

My first love is music which went hand-in-hand with the engineering of sound reproduction which in turn lead me into electronics engineering and then aerospace!

But I never lost my roots and am still into sound engineering.
I love music and especially making electronic music so I thought it would be best to read up on sound synthesis which I am finding very interesting I had some prior knowledge of it because I've used FL Studio for about 4 years so I knew a lot of the terminology already and how most things affected sound but it's that I don't know why it affected the sound so studying it is really beneficial to me. Is electronics engineering to do with like transistors, semiconductors, logic gates etc. ? I like that stuff as well and got introduced to it from playing Minecraft! In minecraft you have this substance called redstone which is like electronic signals and you can build logic gates in it (redstone torches are the minecraft equilavent of transistors) and I built a basic calculator in it before I can't imagine how hard aerospace must be...

If I ever need help with sound synthesis ill be sure to ask for you for help :yep:
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Kyx
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(Original post by eternaforest)
Ah that is interesting, I remember doing the electromagnetic stuff in GCSE. So in the context of sound, when converting the sound (fluctuations in air pressure) to analog, the varying voltage is analogous to the fluctuating air pressure?
I think so
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