Polk CSM impedance question

[Mon40CSMM10]

I've been using the Polk CSM as a center channel for quite a while now, and it seems to be a good match with the other speakers I am using for the front and surround speakers.

I did have one question about the impedance, since the specifications state this is a 4 ohm nominal speaker, compatible with 8 ohms.

Exactly how is this compatibility established with something a receiver that has both 8 ohm and 6 ohm settings?

[VSchneider]

Speaker impedance varies with frequency, and CSM must have some range or ranges where it dips significantly below 8 Ohms, and others where the imp is probably significantly above, so Polk labeled it 4 to be safe. It is nothing like a "true 4-ohm" speaker such as say LSi9, which an average receiver would have trouble with.

A receiver with a 8-6 or 8-4 ohm switch simply limits output (to protect itself) while in the lower impedance setting. It has nothing to do with "matching" to a particular speaker or making it sound better.