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The current however isn't alternating, it's the electrons that are alternating. Current and voltage are scalar quantities, they have no direction. Only the electrons have direction and they are the only things alternating, albeit at extremely low velocity. And there are two wires for an AC circuit, right? Like the ones going into the speakers. Thus, when electrons move in one direction on one the wires they must be moving in the opposite direction on the other wire at the same time.
Edits: 05/27/25Follow Ups:
It's an AC circuit, right?
Audio? then yes
Thus, when electrons move in one direction on one the wires they must be moving in the opposite direction on the other wire at the same time.
Hey, your right, that is the case even if one wire is attached to something labeled ground..
When an amplifier is driving a load (needed to have complete circuit), there is also current flowing in each wire and the magnetic field each wire generates is in opposition / cancels out being so close physically. If you were to run each speaker wire separately, one wire around the right side of the room and the other the left side of the room, that self cancellation would not exist.
Now you have made a series inductor, a big one turn coil which rolls off the top end.
A coax cable is the opposite extreme, minimizing the uncoupled or leakage flux (what looks like the series L).
But you didn't address the underlying question - if the only thing moving in an audio circuit are they the audio signal? Or is the "audio signal" something else? If so, what?
Ok ponder this parallel situation.
You sit down and write a message on paper with a pencil and hand it to a stranger to read.
Which caries the message, the pencil lead, the paper or the meaning of the words you wrote?
From the microphone to the loudspeaker terminals (analogue only), the audio signal is the microphone pressure represented as a proportional Voltage. It turns into power in the power amplifier where the Voltage is amplified and made into a low impedance Voltage source (damping factor is the ratio of the two resistances) to drive the loudspeaker.
The loudspeaker is the reverse, ideally also a linear Voltage to pressure transducer for restoration of the mic signal up to some max intensity.
Yes there are velocity microphones too and since sound propagates as an alternating pressure and particle velocity 90 degrees apart in phase, so that works too.
Let's summarize. I am defining the "audio signal" as the very thing that makes the speakers produce sound, I.e., acoustic waves in the room, I.e., music. Some people believe it's the current or voltage. But I already dismissed those answers because they're calculated values, not actually "signals." Some people believe the signal is an electromagnetic wave, in other words photons, propagating through the copper conductor. Others believe the energy contained in the b and e fields associated with the electromagnetic wave that lie outside the copper conductor is the audio signal. So, what do you think the audio signal is?
I think your missing a key part of this.A microphone detects the sound, it proportionally turns the pressure into a Voltage which is the then the converted audio signal. Microphones all have a "sensitivity" or what Voltage X pressure produces. From here forward, the audio signal is a Voltage signal that represented the pressure.
When recorded on tape, that signal is changes in the magnetic field and polarity, on a record album the audio signal is proportional wiggles in the groove, in stereo those wiggles are _ + 45 degrees off axis.
In an old time movie sound track the audio is encoded into a variable light transmission sound track band. All of these are methods to record / store the audio signal recorded as Voltage signal that represents the air pressure.
In digital format i use, that Voltage is "sampled" and turned into a Voltage measurement every 1/48000 second.How electrodynamic loudspeakers work at level 1 is simple, they cannot produce sound unless something moves the radiator and it is the VC current that results from that Voltage signal that produces force that moves the radiator with the force being the BL product (in Newtons per Amp).
Edits: 05/29/25
If it's current that moves the diaphragm, as you say, then wouldn't it really be the induced magnetic field that's the signal, you know, the thing that interacts with the speaker magnet?
Hi
IF you were to measure a sealed box woofer that had the normal flat frequency response, or one in a vented box, or one in free air, you see the impedance curve is not anything like flat, like the SPL.
IT is that impedance that governs how much current is flowing and how much force the VC is producing.
What you can see clearly it the current flowing is nothing like "flat" magnitude BUT the input Voltage IS flat (same V at any frequency) and in the middle of it's range so is the sound pressure. The Voltage is the signal.
It is the Voltage (being flat vs frequency) that produces the flat SPL vs frequency while the current varies wildly vs frequency. Examine the impedance curve shape being upside down, now you have the shape of the current being applied.
The reasons are described earlier in the Back EMF explanation.
However, for an electrostatic speaker it is the Voltage it self and not current that is proportional to force on the radiator.
I've said repeatedly current doesn't flow, that's a mistaken way to look at this. Current is a calculated number. The only thing "flowing" is free electrons. Back to the drawing boards!
Repetition is not the same as validity, the only current I speak of is what one see's when one measures it. One has two tangible views of what the loudspeaker is doing, the aspects of the acoustic output and the impedance.
Your free to see things any way you think makes sense but what i described is a view that lets you build new things, even invent and patent new types of transducers.
If curious, find a copy of "Handbook for Audio Engineers" the 4th edition has some of my inventions but in the 5th edition I wrote the chapter on transducers and wrote it in plain English instead of heavy engineering and deals with all of this.
We are definitely not on the same page. You can measure how tall an elephant is but that doesn't tell you anything else about the elephant. People believe what they want to believe about the elephant based on its height.
Edits: 05/30/25 05/30/25
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