Originally Posted by el pablo
Thanks for your input Michael!
Still confused as to why you need a more powerful amp to drive low ohm speakers if they require less voltage?
You are getting confused with the electrical engineering vocabulary ...
- Power is the product of voltage (water pressure in the plumbing analogy) and current (water flow)
- Low impedance speakers require more current, not more power
Because most power amps (in an AVR for instance) gave more than enough voltage to drive most speakers to very loud levels, the limiting factor is current capacity. Because a perfect amp (one that is not current limited) will deliver more power to a lower impedance load given a fixed voltage output, people incorrectly equate low impedance speakers with being "more efficient" - they are not. The low impedance speakers do not actually require more power delivered to the speaker terminals, they require more current, which would deliver more power if the output voltage was the same (thus the lay advice of "needing a more powerful amp").
The issue with headphones (and why it seems backwards to you) is that most headphone amps built into AVR's, integrated amps and portable devices are usually voltage limited as well as current limited. In the case of portable electronics, it is a direct result of being battery powered.
The problem then becomes one of high impedance headphones not being driven with adequate voltage. Due to the sensitivity of most 'phones and the very close proximity of the driver to the ear, low impedance headphones do not require current that is beyond the capacity of the common headphone amp since very little power is actually required to drive most headphones.
Therefore, the apparent contradiction of low impedance speakers being hard to drive ("need more power") but high impedance headphones being difficult loads. The issue isn't the physics of the speakers, but the common limitations of the different amplifier implementations.