Why are low impedance speakers harder to drive than high impedance speakers


I don't understand the electrical reason for this. I look at it from a mechanical point of view. If I have a spring that is of less resistance, and push it with my hand, it takes little effort, and I am not working hard to push it. When I have a stiffer spring (higher resistance)  I have to work harder to push it. This is inversely proportional when we are looking at amplifier/speaker values.

So, when I look at a speaker with an 8 ohm rating, it is easier to drive than a speaker with a 4 ohm load. This does not make sense to me, although I know it to be true. I have yet been able to have it explained to me that makes it clear.  Can someone explain this to me in a manner that does not require an EE degree?

Thanks

128x128crazyeddy

Showing 1 response by ghosthouse

I ain’t Al but one of the few things I sort of understand about electronics is Ohm’s law.

From Wikipedia
Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

I (current; amps) = Voltage divided by Resistance (ohms)

At the risk of embarrassing myself, as resistance decreases the current required for a given voltage goes up.

As an example:
1 volt/8 ohms = 0.125 amps;
1 volt/6 ohms = 0.167 amps;
1 volt/4 ohms = 0.25 amps
1 volt/2 ohms = 0.5 amps

So, for a constant voltage, current requirements double going from 8 ohms to 4 ohms and quadruple going to 2 ohms. Current production is a more useful indicator of amp "grunt" than rated wattage (or so I think).

The other thing to remember is that for a given speaker design, resistance might not be constant across the frequency range. Low resistance dips occurring at different points can result in differences in how things sound between two amps with similar wattage ratings but differing in current output capability.

That’s what I think I know.