Impedance is the electrical resistance measured in Ohms (the fellow that quantitified electrical resistance going through a conductor, semiconductor, etc.)
Almost every commercial amp operates easily between 6 and 8 ohms. Many of the cheaper ones have problems when the resistance drops below 4 ohms--usually 2 ohms or so. Which happens quite often in 4 ohm speakers at various frequencies.
My advice to most people buying commercial receivers--buy 6 or 8 ohm speakers. There are plenty of great ones and it prevents you from running into problems with driving speakers, unless you are using runs of wire over 50 feet and more to a speaker. Then use 12 gauge, 10 gauge etc. There are sites that will tell you the diameter and length to use at which impedance and wattage. That is why God created Google--so we can all search these questions out!!!
Oh--by the way--Mr. Lee is correct. Leave it at 8 ohms.
But won't the 6 ohm speaker draw conciderably more power then the rest of my speakers ???
If you connect 2 sub woofers in paralell on a monoblock, one rated @ 4 ohms, and one @ 2 ohms, the 4 ohm woffer makes almost no sound, but the 2 ohm speaker makes twice the sound ++++
The current chooses the path of least ressistance.
I am wondering if the correct thing to do is to add a 2 ohm resistor in series with the 6 ohm center speaker, so that the load on the amplifier is 8 ohms on all channels ????
Won't the other 4 channels get less power, I mean I don't think there's 5 seperate monoblocks in my reciver, as I understand the signal is amplified, THEN it's divided between the 5 channels, but if one of the channels is loaded by a 6 ohm speaker, in stead of an 8 ohm speaker, won't the rest "loose" power ??
Hm...
I'm still wondering what that button on the rear of the amplifyer actually does ??
I mean, "normal" amps, (like the ones I use in my car) are rated @ different wattages depending on the speaker impedance, the lower the impedance, the higher the wattage the amp delivers, logically, since the current flow's easyer where there's less resistance more current will flow, and current times voltage = wattage, and the voltage is almost "constant".
My car amps don't have any switches that select between the different load it can handle, the lowest impedance it can handle is 2x 0.5 ohms or 1 ohm, bridged.
So the 4-8 ohm selector, if I connect 5 x 4 ohm speakers that wil load the amp with 20 ohms.
On the other hand if I connect 5 x 8 ohm speakers im @ 40 ohms, that wil load the amp with "half" the wattage compared to 4 ohm speakers.
So, does the 4-8 ohm switch select between a 20 ohm resistor, and no resistance ???
When @ 4 ohms, the load on the amp is still 40 ohm's in total when moving the button to 4 ohm's ???
Hm...
Then there's this 6 ohm "problem"
Eighter way, the load on the amp wil be 38 ohms, in stead of 40 ohms.