Just letting you know I've done heaps more research and found answers to a lot of my questions in my previous post. I have only questions on Back EMF/Damping Factor now, and I have two different views I've found on them, and I am unsure of which is correct.

The first view, is from a document on a Crown amplifier, it actually states more Back EMF as being a good thing. It states that Back EMF is generated from the voice coil itself, which I think its right. It then says it travels through the speaker cable back to the amplifiers ouput, then returns back to the speaker. Because Back EMF is opposite in polarity with the speakers cone motion, it stops/suppresses the speakers ringing. I dont think this is completely right. It then later says the smaller the amps output impedance, it will not stop the Back EMF, instead it will let it through which damps/stops ringing in the speaker, because as the speaker cone moves out, the back EMF makes it move back in, and vice versa.

My understanding is that Back EMF is a voltage generated by the loudspeaker itself, and bigger motors/drivers and/or heavier cones produce more Back EMF. Thats because the heavier cones are less controlled and more kinetic energy is needed to move them, hence more Back EMF. Because the cone is less controlled, Qms will be rather high, which also means higher Zmax. Back EMF is bad, because it means the cone will keep ringing after the signal is stopped. So that means that amplifiers with high damping factors are needed as they stop the Back EMF from going back to the speaker hence stopping the ringing, especially with high Zmax speakers which have poorer cone control.

So you can see I have a problem, and I cant solve it! Which is right?! Can you offer any advice?

Thanks!
Adrian

Another thought that occured to me, because midrange and tweeters dont produce anywhere near as much back emf as woofers do, its not so important to have an amp with high damping factor for midranges/tweeters as it is for a woofer which produce more Back EMF?

This is good because it allows more powerful motors and therefore larger loads in the system. Cones can be made more massive and still be well-damped. Motors can be made more powerful. But this requires that the amplifier act as a very good current source and sink, because current is directly proportional to motor strength. That's the down side.

So there's the rub. In and of itself, motors that generate a lot of back EMF have strong motor structures and that's a good thing. But if the amplifier isn't a good current source/sink, then the motor isn't strong after all - It's just massive and weak. So if the amp has poor damping ability then a woofer that needs motor braking will perform poorly. Qes will change dramatically and the system won't perform as expected.

One other thing - Consider what happens in a circuit containing transformers (or autotransformers) when back EMF is applied. Tube amplifiers are generally less able to deal with speakers that need motor braking, and this is largely because they have output transformers and have relatively high output impedance.

There are also speaker designs that use autotransformers in the crossovers, and so it is important to consider this if woofers are installed that generate a lot of back EMF. And also watch out for piezo tweeters, since they are a high impedance capacitive load. I've actually heard a few installations where back EMF from a woofer caused the piezo to chirp, even on amplifiers with exceptional damping ability.