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Return from speaker to amplifier, What actually does the amp do with it?

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Posted on August 23, 2015 at 04:38:40
dcuhl
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Location: Mid-Atlantic, USA
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I am wondering exactly what does the amplifier do with the return signal from the speaker? Reason being is that I am working on my own speaker cables and as far as I can tell, its the supply side to the speaker that has the most effect on the sound received from the speaker, provided that the speaker can get rid of the "used" signal fast enough. Anyone care to enlighten me? Thanks to all.

 

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There is no return or supply., posted on August 23, 2015 at 06:54:59
Kal Rubinson
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It is an AC signal and each side is referenced to the other. Without the "return" wire, there would be no sound.

 

RE: Return from speaker to amplifier, What actually does the amp do with it?, posted on August 23, 2015 at 09:31:07
Palustris
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There is no "used signal." Music signals are Alternating Current: for best results both conductors should be the same.

You had better dig out your high school physics book. Go to the chapter on AC and DC circuit theory.

 

RE: Return from speaker to amplifier, What actually does the amp do with it?, posted on August 23, 2015 at 12:23:50
hahax@verizon.net
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Remember electricity works in electrical CIRCUITS. No Circuit which is a continuous loop, no sound.

 

RE: Return from speaker to amplifier, What actually does the amp do with it?, posted on August 23, 2015 at 13:51:58
ahendler
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If you are working on your own cable and have noclue on how electricity works I would find something else to do
Alan

 

RE: I know all that and you have'nt answered the question., posted on August 23, 2015 at 21:20:55
dcuhl
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Location: Mid-Atlantic, USA
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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?

 

Read this, posted on August 24, 2015 at 06:12:35
airtime
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Location: Arizona
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this is a basic article on how a speaker works in relation to the amplifier.

The negative leg can have an effect. Some people have added an additional resistor in line with the negative leg to increase a particular effect.

But as mentioned below it is an electrical circuit and does need to be a complete loop.

 

That's a non sequitor, posted on August 24, 2015 at 06:38:49
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.

 

Hey - you're not the Kirk, posted on August 24, 2015 at 06:45:26
airtime
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Sterilize the entity that asked that question.

 

RE: I know all that and you have'nt answered the question., posted on August 24, 2015 at 07:54:03
Palustris
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You had better dig out your high school physics book. Go to the chapter on AC and DC circuit theory.

 

The Changeling? (nt), posted on August 24, 2015 at 08:13:02
nt

 

It flows back into the secondary of the power transformer, posted on August 24, 2015 at 10:24:38
jedrider
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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.

 

RE: It flows back into the secondary of the power transformer, posted on August 24, 2015 at 16:33:50
dcuhl
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Location: Mid-Atlantic, USA
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Thank you. That answers the question.

 

You're wrong too, posted on August 24, 2015 at 17:19:52
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.

 

RE: Return from speaker to amplifier, What actually does the amp do with it?, posted on August 24, 2015 at 22:02:11
Seriously?!

Clearly, you haven't read Harry Olson's "Acoustical Engineering".


:)

 

RE: I know all that and you have'nt answered the question., posted on August 24, 2015 at 22:21:33
pictureguy
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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

 

RE: You're wrong too, posted on August 27, 2015 at 01:04:29
pictureguy
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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

 

RE: You're wrong too, posted on August 27, 2015 at 04:22:58
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.

 

RE: I know all that and you have'nt answered the question., posted on August 27, 2015 at 07:45:38
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.

:)

 

RE: I know all that and you have'nt answered the question., posted on August 27, 2015 at 09:14:51
pictureguy
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Posts: 22597
Location: SoCal
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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

 

That resistor, posted on August 27, 2015 at 09:53:38
3db
Audiophile

Posts: 1514
Joined: July 22, 2003
effects both +ve and -ve flows so one is really changing the impedance seen by the amplifier. Its got nothing to do with "bleeding off" the return any quicker.

 

It's called back EMF and it has been investigated, posted on August 27, 2015 at 12:58:05
morricab
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By Matti Otala in the 1970s or 80s. Basically at some point the reactive components in the speaker crossover and in the drivers will also "push back" signal into the output stage of the amplifier. if there is no negative feedback, this will be dissipated in the output stage as heat. In extreme cases with transistor amps this can actually shorten the life of the output transistors. Electrostatic speakers are the worst as they will push back nearly 100% of the signal fed to them.

Tube amps without feedback are largely unaffected because they already run hot and dissipate many more watts usually than they are pushing into speakers.

Now, if an amp has negative feedback it can get interesting because a portion of that speaker generated and modulated signal will re-enter the amplification chain through the feedback loop and be re-amplified as distortion. Since it has been pretty mangled by the speaker the signal no longer resembles what went in and is not in time with the original signal...this makes it distortion. THe more feedback, the more of this distortion that is fed into the input stage of the amplifier and sent back around again.

This probably has overall negative sonic consequences for that particular amp/speaker pairing and might be the hidden hand behind so-called "synergy" between components or lack thereof.

 

RE: It's called back EMF and it has been investigated, posted on August 29, 2015 at 23:34:05
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
Unless the output devices have Very Low RdON which allows the speaker VC to dissipate it's OWN back EMF.
This can be demonstrated with the 'thump test'.
Too much is never enough

 

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