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Old 2nd September 2010, 06:14 AM   #1
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Default Pratical amplifier damping factor test for MTM speakers.

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!
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Old 2nd September 2010, 07:22 AM   #2
lineup is offline lineup  Sweden
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Yes, amazing.
And a good observation.
Anyone can now try the same ....
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Old 2nd September 2010, 11:24 AM   #3
AndrewT is offline AndrewT  Scotland
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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.
regards Andrew T.
Sent from my desktop computer using a keyboard

Last edited by AndrewT; 2nd September 2010 at 11:29 AM.
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Old 3rd September 2010, 08:09 PM   #4
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Wow that's a load to digest =)
Yes this probably has to be moved to speakers forum.
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Old 3rd September 2010, 08:37 PM   #5
TerryO is offline TerryO  United States
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It's also been noted that a Damping Factor over about 15 is a waste and provides little, if any, tangible benefit.

Best Regards,
"If you have to ask why, then you're probably on the right track."
quote from Terry Olson's DIYaudio Forum application
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