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In Reply to: RE: Return from speaker to amplifier, What actually does the amp do with it? posted by dcuhl on August 23, 2015 at 04:38:40
The question still remains: What does the amplifier do with the returned signal? Route it straight back into the outlet and by-pass everything else on its way back into the grid?
Follow Ups:
IDEALLY an amplifier has NO resistance so ANY current generated by the speaker as 'Back EMF' should be dissipated BY the speaker itself.
As the amps resistance to this current rises, the damping factor FALLS.
Are you game for a test?
Disconnect your cone speaker from your stereo. With NO wires attached, take your finger and 'thump' the woofer. NOTE THE NOISE.
THan? Take a simple piece of wire or even a paper clip and SHORT the speaker leads together, again with NO amp in sight.
Thump again.
You'll note how 'dead' the second effort sounds. This is the result of a very high, nearly infinite, damping factor. Well, very high, any way.
You've answered your own question.
Too much is never enough
I just read your post, and it brought back flashbacks. When I was a 20-something, installing commercial systems in places like schools, churches, factories, etc., it was pointed out to me that a second use of the classroom P.A. speaker was to listen in on what was going on in the classroom. Yes... the loudspeaker was used as a microphone as well. Makes perfect sense, I just hadn't thought of it before then.
:)
a LONG time ago, a buddy and I EACH bought a Radio Shack 3 Watt CB walkie Talkie. We were going to use it at WORK to stay in touch since we were both working as mechanics in a facility making integrated circuits. This was WELL before Radios / Pagers / Cell Phones.
Long / Short? If we were standing next to or below a PA speaker, the radio would couple INTO that system and you'd be 'on the air' for the entire plant! OOOOPS!
Too much is never enough
In the case of a tube amp, it is back into the secondary of the output transformer.The electrons would go ALL the way back to Niagara Falls (or the TVA, in your case) if not for a series of intervening transformers along the way.
Edits: 08/24/15
In an AC current, the electrons don't flow anywhere, they just move back and forth.
You guys really shoud do some basic reading on alternating current and drift velocity. Here's a couple of starters:
https://en.wikipedia.org/wiki/Alternating_current
https://van.physics.illinois.edu/qa/listing.php?id=3341
http://pfnicholls.com/physics/current.html
https://en.wikipedia.org/wiki/Drift_velocity
The last link has a pretty good example of a 1mm diameter conductor passing a 3 amp current, which equates to 36W into a 4 ohm speaker load or 72W into 8 ohms. If the signal is 60 Hz, the electrons (on average) move back and forth a mere 2.1 micrometers and their net movement over time is zero.
Couple 'gotchas'.
First, don't electrons move at some fraction of the speed of light? 2 microns is only 20,000 angstroms and would be a velocity (linear) of 120 microns per second. That seems REAL slow. Though on AVERAGE, the net movement IS Zero.
And it doesn't matter to your example, but what's important would be VA, based on the power factor of the load. Not that it matters to your example.
I periodically connect a D-cell battery to my speaker leads and 'transfuse' new electrons into the wire. The sound improvement is terrific. I think electrons must wear out.
Too much is never enough
The links I posted explain why the drift velocity is so slow. Basically, copper wire has A LOT of free electrons.
The current determines the number of electrons per second flowing through the conductor. If you take the number of free electrons per unit length of the conductor and divide that by the number of electrons per second flowing, it will give you the bulk velocity of the electrons. For a 10 AWG speaker wire carrying 1 amp, the velocity is just 1.77x10-6 m/s.
Like I said, there's a lot of free electrons in copper wire. In a typical 3m length of 10 AWG speaker cable, about 1.34x10^24 of them, which is equivalent to about 60 amp-hours. So a D-cell isn't going to cut it. You would need to empty a car battery to move electrons all the way through the 3m length of wire.
Thank you. That answers the question.
You had better dig out your high school physics book. Go to the chapter on AC and DC circuit theory.
If you really did "know all that" then you would know your question doesn't make sense because there's no such thing as the used or returned signal.
The amplifier produces a time-varying voltage difference between the + and - output terminals. That voltage difference causes alternating current to flow back and forth through the speaker in both directions. The same alternating current flows in both the + and - legs of the cable simultaneously.
Sterilize the entity that asked that question.
nt
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