Nominal vs Minimal Impedence

[Canada]

What is the difference between nominal an minimal impedence? I have absolutly no idea what nominal impedence means.

[Clark Kent]

When shopping for speakers, you will see figures stating the nominal impedance of a speaker (most speakers have a nominal impedance of between 4 and 8 ohms). This is the speaker's average resistance to the flow of current through the circuit going from the amplifier into the speaker and back to the amplifier.

However, this figure is only the average impedance rating across all frequencies into which the speaker produces output. In reality, the impedance may drop at some points to 2 or 3 ohms and may reach 40, 50 or even 60 ohms at other frequencies. For this reason, it is beneficial to have a strong amplifier able to produce large amounts of power down into small impedance loads. Generally, receivers should be mated with speakers having a nominal impedance of 8 ohms or so while separate amplifiers may be used with speakers with nominal impedances of 4 ohms or so. A speaker with an 8 ohm nominal impedance will not generally have as low a minimum impedance as a speaker with a lower nominal impedance such as a 4 ohm speaker. The most important impedance rating to be aware of is that used with speakers.

[richteer]

Originally Posted by Clark Kent

When shopping for speakers, you will see figures stating the nominal impedance of a speaker (most speakers have a nominal impedance of between 4 and 8 ohms). This is the speaker's average resistance to the flow of current through the circuit going from the amplifier into the speaker and back to the amplifier.

However, this figure is only the average impedance rating across all frequencies into which the speaker produces output. In reality, the impedance may drop at some points to 2 or 3 ohms and may reach 40, 50 or even 60 ohms at other frequencies. For this reason, it is beneficial to have a strong amplifier able to produce large amounts of power down into small impedance loads. Generally, receivers should be mated with speakers having a nominal impedance of 8 ohms or so while separate amplifiers may be used with speakers with nominal impedances of 4 ohms or so. A speaker with an 8 ohm nominal impedance will not generally have as low a minimum impedance as a speaker with a lower nominal impedance such as a 4 ohm speaker. The most important impedance rating to be aware of is that used with speakers.

Couldn't have said it better, though I'd add that some receivers are 4 Ohm rated, so one can use lower impedance speakers with those.