As to why impedance _matching_ (in the proper sense of the term) of amps and speakers is usually NOT desirable: basically the reason is that the efficiency is very poor.
Let's suppose you have a power amplifier with an output Z of 0.1 ohms, and you want to get maximal power out of it. It might seem that this would deliver the most power into a 0.1 ohm speaker... and you could make a 0.1 ohm speaker by tying a bunch of regular speakers in parallel. The problem is that for this to work, the amp would need to be able to deliver enormous quantities of current at a very low voltage, and it's not feasible to design one that could do that. Conversely, let's say you have a 8 ohm speaker. For a given source voltage, maximal power would be delivered to the speaker when the output also has a 8 ohm internal impedance, but the problem is that under that condition you are burning an equal amount of power in the source: a lot of work is getting done by the load, but the system as a whole is only 50% efficient. In practice you are better off designing for efficiency, and upping the voltage. At first it is not really obvious why it works like that, but if you imagine the two extremes of the situation it makes more sense. If you put a short circuit (using a very large wire) across a battery, the battery will heat up but the wire will not. No work has been done outside the battery, so the system is 0% efficient. Now consider an infinitesimally tiny load attached to the battery. Efficiency is now 100% - the battery will not get hot because it isn't strained, but not much work is being done either, because the load is insignificant. It should be more intuitive now that the maximal power transfer would happen when the load is being driven "as hard as the source can push", but this is not the same thing as maximal _efficiency_. Since solid state amps naturally have a very low Z, it does not make sense to put an additional resistance at the source - that would just waste power in the amp. Instead we enjoy higher efficiency by using a 4 to 8 ohm load, and use higher voltages to reach the output power levels desired. So that is why if an amplifier says it has "4 ohm outputs" what they're really saying is "this output can make voltage and current levels suitable to power a 4-ohm load", not "this output has a 4ohm impedance". -- seanadams ------------------------------------------------------------------------ seanadams's Profile: http://forums.slimdevices.com/member.php?userid=3 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
