THAT.Here's me doing a quick test.
My oscilloscope connected directly to an old 10" woofer and me rapping the dust cap with my knuckle. (ie, the cone moving inward (toward the frame) with my rap.)
Dave.
FWIW, I commercially make speakers, and each and every time I finish one, I check both that I have continuity, phasing and even that it´s actually magnetized (I might have forgotten to
)I almost never use a battery (which I should have to specially grab and connect) or even a power supply, unless I have one within arm´s reach, but simply connect meter probes: Black to Black and Red to Red and move cone in-out a couple times.
200mV scale but do not even read "the number" , simply watch the polarity sign: when moving backwards I must see the "-" one, when forward no sign (which means positive).
Suggest everybody tries it at home, it takes all of 10 seconds.
Applying this to parallel speakers (obviusly connected in phase), pushing one back will create a negative voltage which will push the other one back too.
There was some confusion in this thread about "current", the confusion disappears (I hope) when thinking voltage which is the primary parameter here, "Current" and "displacement" are derived from "Voltage" and will follow whatever it dictates.
Yes, of course.
Induced movement is very small as you can imagine, would need a microscope to clearly see and measure it with my eyes or shine a thin beam laser diode just tangential to dome and a photodiode at the other side, again to measure it, but I have DEFINITELY confirmed by experiment that:
1) pushing cone backwards generates a negative voltage (as I mentioned above). <-- experimental fact.
2) that a negative voltage applied to secondary/passive speaker makes it go backward. <--- experimental fact
now add 1+2.
Part of experimental conditions is that both speakers are in parallel and in phase, of course.
And that speakers are closer than, say, 3400 km, so voltage at one pair of terminals can be considered simultaneous with that present on the other pair within 1% error.
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I'll have to update my conclusions on this one (sheepishly
). It only optically appears that the 2nd cone is moving out, however this is a bit of an illusion.I connected a scope and reworked my experiment to just push and hold driver#1 and set a physical edge to driver#2. The scope definitely shows an initial negative pulse across the terminals and that does pull driver#2 down slowly, However, as soon as driver#1 stops moving, it causes driver#2 suspension to return to the null position (overshoots actually) and it does appears that it moved out because the return movement is faster and more pronounced. It's a tricky thing to separate.
My apologies for causing any confusion on this.
You are not the only one with some reason to feel sheepish. Got some things wrong myself along the way, too. Probably we aren't the only two either...
Oh, well. Hopefully everyone is on the same page now. That's the important thing.
That one is being sold as a novelty item but there used to be a real world commercial device based on that.
I am a Photographer, classic old type with metal and glass cameras, chemically developed fiilm and paper, etc.
Remember browsing old Photography magazines, with whole page blanket ads by large shops, think Adorama, B&H Photo, etc. , offering myriad gadgets, including a "fake telephoto" lens add-on, exactly what you show: a black tube, with threads at one end to screw it on a regular camera lens, with a 45 degree mirror inside plus a side opening.
Great to take bikini girl pictures at beaches, shy/shady people who did NOT want to be photographed, etc.
Still very much available:
https://fotodioxpro.com/products/fltr-spy
In the old days of audio showrooms many pairs of speakers could be selected (one pair at a time obviously.) The non-selected pairs would have their leads shorted in an attempt to not effect the pair playing.
Visualize a whole bunch of interlocked mechanical pushbuttons and you have the idea. I repaired one. What a nightmare.
Dave.
Visualize a whole bunch of interlocked mechanical pushbuttons and you have the idea. I repaired one. What a nightmare.
Dave.