Pratical amplifier damping factor test for MTM speakers.

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Hi guys,

If you have an MTM speaker, and the amplifier turned off, tap any midwoofer's cone very gently,
and you can notice the 2nd cone move in and out as well.
My woofers each have their own ported enclosures.

With the amplifier turned on, but no source playing, try tapping the same cone again.
Depending on your amp's damping factor, notice how the 2nd cone resists motion.

I tested on my low damping factor SE solid state amp, the 2nd cone moves a lot!!
With another amp of 800 damping factor, the 2nd cone refuses to budge!
Quite amazing!
short out a generator and try to mechanically move it.
It resists. Why because you are inputing power and it is outputting a proportion of that power.
Ah, you say, got ya. The output is shorted, therefore there cannot be any power output.
But there is measurable resistance in the generator circuit. Passing any current through this circuit resistance is power.

Now add a resistor across the generator output in lieu of the short.
Turn/move the generator. Not quite as much resistance. Why because the power output has been reduced and so the power input is also reduced.

A voice coil is normally thought of as a motor: input electrical energy and out comes some movement.
But it works (badly) as a generator. Input some movement and out comes some electrical power. Changing the value of the resistance across the speaker terminals changes the power it is required to generate. In the extreme changing the resistor to an open circuit and the generator cannot pass any current and so cannot deliver any power. Now the resistance to movement is reduced to just the friction to turn it over, or move the voice coil against it's Vas.

Basic yr8/9 school physics.

another example used by anyone that races slot cars. The motor becomes a generator when the power trigger is returned to it's OFF stop. The motor is shorted through the controller and the motor slows very rapidly. This is dynamic braking. It is used a lot in industry.
It is getting used to improve the performance of electric and hybrid electric vehicles.

Do we move this topic to speakers or to everything else? I cannot see it staying in Solid State.
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