Electrical
Ohm's Law
01 — Definition
V = I × R, and power P = V × I = V²/R = I²×R. Every electrical calculation in AV follows from there. At the same voltage, doubling the resistance halves the current. And four 8Ω speakers in parallel make 2Ω — a load the amplifier has to be able to take.
02 — In the field
Always work out the total impedance of a speaker array before you connect it. Put a 2Ω load on an amp rated for 4Ω minimum and it will overheat within minutes at full power.