Over 30 years ago, when Wilmslow Audio was still located in the Cheshire town of Wilmslow, I had the privilege of being given free run of their loudspeaker comparator room.
Just me, a huge room full of constructed kit speakers and an impressive array of switches. No salesperson to distract me from my auditions - audio heaven!
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Did the experiment as you suggest. I believe convention is that the positive terminal is determined for outward moving cone. I applied a positive voltage to the +ve winding and the cone moved outward. I tapped/pushed a 15" driver from the inside and it generated a +ve voltage/pulse, hence this confirms your findings.
However it can be considered that the direction of travel is determined by the signal magnetic field in relation to the fixed magnetic field of the magnets. The direction of travel is determined from zero by the difference between the net fields. This suggests that being driven as a motor the net field can be greater than the fixed field for positive signals, thereupon moving a speaker outwards, yet as a generator can still produce positive polarities yet the net field can be negative, wanting to drive the speaker in reverse. Don't know if this makes sense.
The mistake seems that movement is a function of net field.
We used to learn this when we were kids:
https://jetcastricum.nl/wp-content/uploads/2011/10/Bouwhandleiding-spijkermotor.pdf
https://docplayer.nl/11477842-Spijkermotor-dit-moet-hem-worden.html
https://jetcastricum.nl/wp-content/uploads/2011/10/Bouwhandleiding-spijkermotor.pdf
https://docplayer.nl/11477842-Spijkermotor-dit-moet-hem-worden.html
Looking at it from a voltage point of view can be confusing. Since the drivers are connected + to +, - to -, and if you assume for the argument that the wires have 0 resistance, then whatever the voltage at the + terminal of driver A is, it will be the same at the + terminal of driver B. The caveat is that one driver is a generator and the other the load.
A better way to look at this is through the current. When you push driver A IN a current is generated in the VC that opposed that motion and attempts to push driver A OUT, or at lease resist it from moving in. Say that current flows in the VC in the direction of the + terminal to the - terminal. Thus the current leaves driver A through it's - terminal. It then enters driver B through it's - terminal and flows through driver B's VC from - to +, the opposite direction of driver A. Now, recall that this current, when flowing through driver A, (+ to -) generates a force pushing out. Since it flows through driver B in the opposite direction (- to +), the force it generates in dirver B pulls driver B inward. Thus both driver A and B move in the same direction when you push on driver A.
A better way to look at this is through the current. When you push driver A IN a current is generated in the VC that opposed that motion and attempts to push driver A OUT, or at lease resist it from moving in. Say that current flows in the VC in the direction of the + terminal to the - terminal. Thus the current leaves driver A through it's - terminal. It then enters driver B through it's - terminal and flows through driver B's VC from - to +, the opposite direction of driver A. Now, recall that this current, when flowing through driver A, (+ to -) generates a force pushing out. Since it flows through driver B in the opposite direction (- to +), the force it generates in dirver B pulls driver B inward. Thus both driver A and B move in the same direction when you push on driver A.
Conventional current flows from + to - in a load, and from - to + inside a generator. Above diagram appears to show electron current, which is not the standard convention for physics.
Moreover, measurements show driver direction (in/out) correlates with voltage, whether the driver is a generator or a load.
Moreover, measurements show driver direction (in/out) correlates with voltage, whether the driver is a generator or a load.
Then driver B would move out too. Both drivers move in the same direction whether acting a generator or as a load. The direction of movement is correlated with voltage, not current.
Really? Are you saying, in college physics texts positive current flow is defined by the direction of travel of a negatively charged particle?
Not to mention that the original figure is correct because the the drivers are moving inward. Thus the current would indeed flow from the - terminal to the + terminal for driver B, as typically labeled by a manufacture.
You really are missing the point which is the current would flow in the opposite direction. And last I knew the force that accelerates the driver is a function of the current through the VC, F = BL x I.
If a generator then for the same motion, say, inward, then the force would be -F which makes I negative too. V however stays the same. If acting as a generator then the same motion, in or out, correlates with the same terminal voltage polarity. What changes is only the direction of the current. If you don't believe it, you might try measuring it yourself. Other people have already done the experiment and know what happens.
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So what does the notation of + and - mean for a driver subject to an AC signal other than the direction the cone will move when a + voltage is applied? As I said, the original figure is correct because if the driver moves out when a positive voltage is applied (which is the convention) then when the driver moves in the current must be in the - to + direction in Driver B, the driven load.
There are two cases. The first, which I stated was obviously addressing the driven drive, B, "the force which accelerates the driver". The second in the case where an external force is applied to accelerate the driver, A. In that case, the external force is countered by the force generated by the motor structure and that forces is still BL x I. Now, that force in Driver A is in the outward direct where as in driver B it's in the inward direction. Thus if you take the outward direction as positive, then F = BL x I, which is positive for driver A. But the force on driver B is still F = BL x I but in the negative, or inward direction. If they are both equal to BL x I but opposite in direction, how can that be? Because you have to consider the direction of current flow. Regardless of how you define current,"I" in driver A flows in the opposite direction of that in derive B, which was the point of the figure.
Perhaps part of the problem is that you interpreted the labels of the driver terminals + and - as the potential difference between the terminals. But the text clearly states them as the + and - terminals of the drivers, (i.e., manufactures notation), not the potential difference between them. Perhaps that could have been clearer.
Yes, probably best to make a note on the drawing if polarity markings are not in conventional notation.
Other thing had to do with if one driver is pushed in, then which way does the other driver move, in or out? That resulted in a lot of confusion in the thread, but eventually some consensus was reached by a few people taking some measurements, along with some visual observations. Bottom line is that both drivers always move in the same direction. That's true if both are loads, or if one is a generator. However, it can be visually confusing since the generator only produces current while its in motion, and then the other speaker driver rebounds with a little overshoot when generator motion stops. IOW, it can sort of look like when one driver is pushed in then other driver moves out at the same time, although that's not exactly what happens.
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(If we're on the same page here), this is one of my first year texts..
I tend to follow circuits from the ground up.
Okay, fair enough. Have to say for myself that its always easier to think about circuit operation from schematics if current flows through diodes and bipolar transistors in the direction of the arrows. BTW, there was a copy of that book on ebay for ~$11 and with free shipping. Couldn't resist, so to speak.
To express this somewhat differently, a stationary coil in a magnetic field doesn't generate a potential across the coil, hence physically displacing the cone in an outward direction can only generates a positive pulse as returning to zero. Negative voltage rebounding occurs from any inward physical movements from the positive displacement peak that can come from tapping, etc.
The testing of speaker direction can be done using current or voltage. This is to state that there is no requirement for monitoring current direction in using voltage as the test method, nor monitoring voltage in using current direction for testing. Of course if you flipped the magnet around the speaker cone would move in the opposite direction and the positive identified terminal would require being flipped.