Originally Posted by Grendaizer
Forgive the ignorance as i'm very new to the A/V scene but does this mean it's possible to "fry" a receiver by attaching speakers with big loads (what characterizes a big load by the way?) I thought it was possible to blow speakers by applying too much amplification but not the other way around.
Not by applying big loads, but the reverse - if you apply a smaller load (say a 4 ohm speaker) to an amplifier that is limited in its ability to deliver current, sooner or later, depending on the volume applied, the current demanded exceeds the amplifier's (receiver's) abilities and the receiver self destructs or shuts down.
Ohm's law is Voltage = Current X Resistance
In the speaker world, and in the Electrical Engineering world, resistance is really impedance.
So if you have an 8 ohm speaker, applying a voltage of 10 volts, the current demand is:
Current (I for us geeks) = Voltage.. 10 in this case / 8 ohms = 1.25 Amp.
The same for a 4 ohm speaker is:
Current = 10 / 4 ohms = 2.5 Amps.
So the smaller the impedance for a given voltage (volume, eventually), the higher the current required. The larger the voltage applied (volume), the more current is demanded. Eventually, you reach the maximum possible for a given amplifier / receiver, and bad things happen, since Ohm's law has to be satisfied.
One extra kicker is that speakers are not static, but active loads; the impedance varies over a given applied frequency range, so a given speaker may be 8 ohms at one frequency, but 6 ohms at another. At a constant volume (voltage).
This means that your speaker may have one value (and demand X current) at one frequency (say midrange music) and quite another (say 1.5X) at another frequency (say at the higher ranges of music).
Your receiver had better be able to handle the impedance range of a particular set of speakers.