Under pwer vs. Over power

Wow, thanks for the explanation.  Now I know I am out of my league here, so please don't take this as me disagreeing.  I am just playing devils advocate to learn. 

But is the cone held in place long enough that there is lack of air movement?  I can see this maybe at a REALLY low frequency like say 5 Hz.  But even at 20 Hz the change to polar extremes is pretty quick.  In fact that video I linked in that other thread was taken with the subwoofer playing at about 15 Hz.  And yet it is moving back and forth at a decent rate.  I suppose one difference between a sine wave and a square wave is that acceleration is attempting to change at a much greater rate with a square wave.  Or is that incorrect?

Steven Kephart

Adire Audio

Now don't get me wrong.  I think explaining it to be similar to DC offers a great visual aid for those learning. 

That's a very good question.  In my experience, well-made woofers can probably handle the extra heat much better than more poorly designed and built ones.  Cheaper speakers use cheaper components, of course.  You are correct that a square wave attempts to change state (phase) instantly.  Since infinite acceleration is impossible in any system with mass, the loudspeaker cannot react at the same rate as electricity can.  In this case, a higher frequency square wave can cause the voice coil to "twitch" as it tries to alternate between extreems and it cannot keep up.  It simply heats up in this case.  Tweeters are prone to damage from clipping in this manner. 

In this case the amp will receive a lower signal than it is adjusted for and will not increase output at the same rate as the HU (it won't get as loud).  You want the maximums matched so that the amplifier output increases at the same rate as the HU preamp output.

This is generally correct.

Forgive me for going off on a tangent that has little to do with the original topic.  But this is a topic I am still trying to fully comprehend.  I think the mistake that most people make, including many engineers we have found, is that they think in terms of acceleration, rather than change of acceleration.  From what I have been told, speakers are constant acceleration devices.  Now with a squre wave as far as I can tell the rate in change of acceleration is much higher because it is going directly from infinity to zero, rather than a smooth transition with a sine wave.  Now mass will effect a square wave just like a sine wave.  It won't effect the rate in change of acceleration because mass is constant.  It will only limit the peaks of those waves (SPL).  However the inductance within a speaker will effect the rate in change of acceleration since inductance tries to keep current from changing.  This should make for an interesting looking wave form produced by a speaker with high inductance trying to produce a square wave.

But then maybe I'm wrong.  Maybe in such an extreme instance like a square wave, mass does start to effect the transient response for the reasons you mention.  But then as I mentioned above, inductance is effecting it as well.  I would guess one or the other would dominate.  But which one?

Steven Kephart

Adire Audio

I am not a loudspeaker designer, but from my understanding of physics and electricity you must take into account both the inertia of the mass being accelerated (any change of momentum or directions requiring acceleration in order for the change to occur) AND you must take into effect the electro-magnetic behavior of the voice coil windings as current carrying conductors in a magnetic field.  Both Newton and Faraday have a say in this one, I suspect. 

I think both mass and inductance/impedence have an impact on transient reaction and response, and both work together to determine the ability of a loudspeaker to reproduce any soundwave.  Which has a greater impact probably depends more on the specific parameters at each measurment than on any generally predictable behavior.  I'd be willing to bet the contribution from mass and the contribution from inductance, reactance, resistance, flux density, etc. changes over the loudspeaker's response curve and as input levels change; at some times one contrinutes more and at other times other factors do.

This is conjecture on my part, but it seem to fit with my basic understanding of the phenomenon occurring in a speaker voice coil.  I could of course be wrong!

That is correct, and a VERY good point.  However it wouldn't be moving back and forth at a slower rate because that would change the frequency produced.   It just means that for every doubling of static movement, there is 4 times more air moving past the coil (or is that even correct?).  So the question still stands.  However this does become even more complex when we add enclosure effects into the mix.

Steven Kephart

Adire Audio