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# AC or DC - How headphones and amps work! - Page 2

Quote:
Originally Posted by HamilcarBarca

The definition of alternating current has always been something like those Free Dictionary quote. "Mains" power is an example of A/C, but it hasn't ever been the definition.

So I listen to a music signal amplified and you listen to "AC" the difference is what       apart from how we interpret a definition ????

Quote:
Originally Posted by ruffra

Quote:
Originally Posted by HamilcarBarca

The definition of alternating current has always been something like those Free Dictionary quote. "Mains" power is an example of A/C, but it hasn't ever been the definition.

So I listen to a music signal amplified and you listen to "AC" the difference is what       apart from how we interpret a definition ????

I was going by The Free Dictionary entries from the page you cited without realizing you were repudiating the definitions. I misunderstood. Sorry.

Quote:
Originally Posted by ruffra

So I listen to a music signal amplified and you listen to "AC" the difference is what       apart from how we interpret a definition ????

The music signal is already alternating from + to - on the "red" positive wire, speed dependant on frequency. Thus it is, in essence, an alternating current, or AC.

There is no interpreting any definitions differently here.

It is not sinus wave 50 hertz alternating "current" at 110/230 Volts, we can clearly agree on that. Youtube: killing woofer 110v. It does make a sound, but only very short.

Quote:

Originally Posted by jcx

can't you guys posting beyond your knowledge find a elementary "how things work" site to check your "facts" [edit: the post's got better even as I wrote so recent posters needn't get bent out of shape by this comment]

while "AC" literally stands for alternating current it is used more generally - alternating voltage is of course implied, and any signal that averages to zero may be described as "AC" - even when voltage and current aren't involved

sound is "AC" - sound waves propagate as alternating compression and rarefaction of the local air pressure - the average of the air pressure is not detected as sound - is not recorded and is not reproduced on playback - only the the "alternating" part of the air pressure (and velocity) is "audio signal" - usually only the AC components with frequency > 20 Hz (and less than ~ 20 KHz) are considered "audible"

dynamic transducers (most headphone drivers) create "alternating" sound pressure as their diaphragms move back and forth in response to the alternating audio frequency current in their voice coils - the average of the current and voltage should be as close to zero as possible - any small "DC" component to the drive signal forces the voice coil/diaphragm off center and may increase distortion; large DC signal may over heat the voice coil, melting plastic or glue and destroy the headphone

electronic amplifying devices amplify small audio input signals by modulating a DC, constant polarity power source in response the control signal - some circuits/devices have a DC component on their output that must be blocked/removed before the amplified alternating current/voltage signal reaches the headphone

the amplifier circuitry may get its power from a "DC" battery source or it may use the wall outlet "AC" mains line current and convert that into the DC needed by its internal signal amplifying components

a common gnd wire (and the standard TRS jack plug) does cause some L/R channel crosstalk - typically it is very low since the wire resistance is a small fraction of an Ohm and the headphone drivers many 10s of Ohms

jcx has posted in the DIY section for years.  Some may have a disagreement with him about amplifier topology preferences, but he knows whereof he speaks in this area and AFAIK, he's actually in the opamp business, at least with applications.

OK I will try and make this my last post on this subject matter.

I still cannot get my head around a convention that labels an amplified signal using components that are under DC power and output from Amplifier Binding Posts that are positive and negative  to be called “AC” even if the output wave shape is only a 60Hz sinewave.  I just don’t get it.  Perhaps its my training in Heavy electrical power engineering that’s give me this hang up as I never considered this to be AC and it was never really referred to  in the AC circuit theory as such. (Or perhaps I skipped that Lecture)

However if current nomenclature refers to it as such then so be it.  But just providing you don’t want me to change my Binding posts to Live and Neutral for the “AC” signal , cause that’s just going to make trouble.

I think I will now call it a DC output with an AC waveform. How about that folks , does that make you feel any better??

Anyway I’m going back to listen to some ACDC on my Philips X1’s as I find that a lot more interesting.

Edited by ruffra - 2/2/13 at 5:39am
Quote:
Originally Posted by ruffra

OK I will try and make this my last post on this subject matter.
I still cannot get my head around a convention that labels an amplified signal using components that are under DC power and output from Amplifier Binding Posts that are positive and negative  to be called “AC” even if the output wave shape is only a 60Hz sinewave.  I just don’t get it.  Perhaps its my training in Heavy electrical power engineering that’s give me this hang up as I never considered this to be AC and it was never really referred to  in the AC circuit theory as such. (Or perhaps I skipped that Lecture)
However if current nomenclature refers to it as such then so be it.  But just providing you don’t want me to change my Binding posts to Live and Neutral for the “AC” signal , cause that’s just going to make trouble.
I think I will now call it a DC output with an AC waveform. How about that folks , does that make you feel any better??
Anyway I’m going back to listen to some ACDC on my Philips X1’s as I find that a lot more interesting.