Magfan, impedance actually is pretty important. I've read the whole thread here and not seen any of the important issues addressed- here they are.
1) The lower the impedance, the more power you will get from a transistor amp, within the limits of that amp's individual abilities. This is not to say that it will sound better- low impedance is only an advantage if you want sound pressure. The effects that low impedance loads have on any transistor amp are otherwise bad for sound **quality**.
2) Tubes prefer higher impedances as well but for different reasons. Reducing the impedance of the load will cause a tube amp to loose bandwidth, power and increase distortion, even if there are taps on the output transformer for the load. Many tube amplifiers will actually run cooler on higher impedances- the output transformer or output section if there is no transformer will be more efficient.
3) Higher impedances thus sound better on both transistors and tubes, all other things being equal, a 16 ohm speaker will thus sound better than a 4 ohm speaker. 'All other things' seem like they are never equal, but going to 16 ohms is an easy way to make a speaker seem more transparent and relaxed, regardless of the amplifier.
4) Lower impedances demand far more out of the speaker cable, for best results it has to be kept short and with larger conductors. Higher impedances are far more forgiving of speaker cables- you can use longer lengths and lesser materials and not loose resolution.
In general, higher impedances are preferred if sound **quality** is your goal, low impedances are preferred if sound **pressure** is your goal, but only with transistor amps. Tube amps will not loose power with higher impedances but transistors usually will.
BTW, the difference between sensitivity and efficiency is worth discussion here. Sensitivity is 2.83 Volts at 1 meter, Efficiency is 1 watt at 1 meter. Let's say you have a system that uses 2 8-ohm drivers in it. Furthermore, the drivers are 90 db 1 watt/1 meter. If the 2 drivers are in parallel (4 ohms), the sensitivity will be 93 db, but the efficiency will still be 90 db. If the speakers are wired in series (16 ohms), the sensitivity will fall to 87 db, but the efficiency will again be 90. IOW, the sensitivity of the speaker can be affected by the impedance, but does not affect the actual efficiency.
Depending on the amp, this can have a big effect on how it will behave on that speaker! Going from 4 ohms to 16 ohms will cut the power of most transistor amps by 75% (although it will sound better). Let it not be said that impedance is unimportant :)
1) The lower the impedance, the more power you will get from a transistor amp, within the limits of that amp's individual abilities. This is not to say that it will sound better- low impedance is only an advantage if you want sound pressure. The effects that low impedance loads have on any transistor amp are otherwise bad for sound **quality**.
2) Tubes prefer higher impedances as well but for different reasons. Reducing the impedance of the load will cause a tube amp to loose bandwidth, power and increase distortion, even if there are taps on the output transformer for the load. Many tube amplifiers will actually run cooler on higher impedances- the output transformer or output section if there is no transformer will be more efficient.
3) Higher impedances thus sound better on both transistors and tubes, all other things being equal, a 16 ohm speaker will thus sound better than a 4 ohm speaker. 'All other things' seem like they are never equal, but going to 16 ohms is an easy way to make a speaker seem more transparent and relaxed, regardless of the amplifier.
4) Lower impedances demand far more out of the speaker cable, for best results it has to be kept short and with larger conductors. Higher impedances are far more forgiving of speaker cables- you can use longer lengths and lesser materials and not loose resolution.
In general, higher impedances are preferred if sound **quality** is your goal, low impedances are preferred if sound **pressure** is your goal, but only with transistor amps. Tube amps will not loose power with higher impedances but transistors usually will.
BTW, the difference between sensitivity and efficiency is worth discussion here. Sensitivity is 2.83 Volts at 1 meter, Efficiency is 1 watt at 1 meter. Let's say you have a system that uses 2 8-ohm drivers in it. Furthermore, the drivers are 90 db 1 watt/1 meter. If the 2 drivers are in parallel (4 ohms), the sensitivity will be 93 db, but the efficiency will still be 90 db. If the speakers are wired in series (16 ohms), the sensitivity will fall to 87 db, but the efficiency will again be 90. IOW, the sensitivity of the speaker can be affected by the impedance, but does not affect the actual efficiency.
Depending on the amp, this can have a big effect on how it will behave on that speaker! Going from 4 ohms to 16 ohms will cut the power of most transistor amps by 75% (although it will sound better). Let it not be said that impedance is unimportant :)