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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 gs5556

gs5556
1,209 posts
 
For the same reason you lose water pressure in the shower when the toilet is flushed. More water is drawn, lowering the pressure in the tank. When the speaker has a high impedance, it’s like a faucet that is slightly open. The pressure (voltage) in the tank (amplifier) is maintained as there is little flow (amperage) through the piping (speaker cables). When the impedance drops, the faucet opens which draws more water (amps) causing the pressure (voltage) to drop. If the amplifier does not have enough ’pressure’ it cannot supply the current for the speaker driver to move.

That is why amplifiers that maintain voltage throughout the impedance swings of speakers are heavy and expensive. They have to act as a voltage source regardless of the current demands of the speaker. This requires a bigger transformer, bigger power supply capacitors and high current output devices to put it all togther.
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