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What’s an Ohm?
The ohm is the unit of measure for impedance, or electrical resistance.
What does this have to do with your home theater? It affects how much power your amplifier produces.
Power = voltage^2/resistance. Anything that is fed an electrical signal provides resistance. The higher the number in ohms the higher the resistance. Many loudspeakers are rated at 8 ohms. (This rating is usually listed as “nominal” because resistance is variable-- it changes over the frequency range.)
It is usually not too high resistance that we have to worry about, but too low resistance.
Say you have an amp that will produce 25 watts (power) into 8 ohms. If you show the amplifier a 4 ohm load, you decrease resistance and increase power because any given number will be larger when divided by a smaller number (80/8 is less than 80/4).
As the resistance decreases and power will increase (a theoretically perfect amplifier would double in output) the current will also increase because Ohm’s law states that current = voltage/resistance (power = voltage^2/resistance).
If the amplifier has the capability to produce this much current and dissipate the heat, you will be fine, but if not, you will over heat the amp and may ruin it or at the least trip the protection circuitry. You should always know the limits of your speakers and amplifier to avoid damage.
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