Impedance of biwire-able speakers

Sean hits the nail on the head. This is a question for your speaker manfacturer assuming they would tell the truth. Nominal impedance is sort of an average of impedance across the frequency spectrum. You probably can find a frequency vs impedance curve either from a review, your manfacturer or maybe your speaker manual. Once you determine the crossover point you can look at that curve and get an idea of what impedance you are facing . Actual impedance is determined based on the amps output impedance together with the speakers impedance(Thanks, Raul). Hopefully your speaker will have a relativey smove curve.
The other problem is you really need to have an separate volume control for each amp. It would be helpful to know what your amp and speakers are.
Congratulations on recognizing a point I never thought about.

Greg: To take that a step further, the nominal impedance of the speaker cable is also inserted in series with the speaker as part of the load. This is why some cables are more neutral in some systems than others. Running your .08 ohm output stage from your solid state amp into a 60 - 100 ohm loudspeaker cable to feed your 4 - 8 ohm speaker seems a bit ridiculous to me, but hey, what do i know??? : ) Sean
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Thank you both, Sean and Gregadd. I am new to audigon and am finally delving into higher end audio for the first time. I have been a 'wanna-be' audiofile since my college days in the 80's, but have let marriage and kids take the front seat. I am asking about speaker impedance for two reasons. I do understand that speaker load is dynamic and subject to several factors. But, several years ago I fried one channel of my Phillips FA80 integrated amp by driving 2 pair of speakers simultaneously - (1) 4 ohm pair (KEF Q15) and (1) 6 ohm pair (MB Quart somethings...). So if I get the amp fixed and want to use both channels to drive the pair of bookshelf KEF Crest 2's I just bought, I want to make sure I dont burn it up again. Second, I have found a mint pair of KEF 104.2's and will be shopping for new components to drive them; but in the mean time don't want to mess my receiver up if I 'bi-amp' them with both channels (of my Onkyo TX8511 receiver). I am on a tight budget for a while, but refuse to do without my music. I want to experiment and learn, but can't afford to run out and buy a hi-end preamp and amps right away. I have just received my Canare 4S11 cable and want to have some fun! Thanks for your time.

You're losing me here. Bi-amping a pair of stereo speakers would mean using four channels of amplification i.e. one channel for the left woofer, one for the left tweeter, one for the right woofer, one for the right tweeter, etc... Is this what you are talking about or can you better describe what it is you're interested in doing? Sean
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Allow me to get touchy feely. To be an audiophile all you need is a desire to get the most out of recorded music. I started out with a table radio listening to FM. As I write this I am at my home office desk listening to my mini system(purchased from Best Buy under $1k).
Secondly, you are not talking about bi amping. If you are running two pairs of speakers off one set of speaker connections, you either run them in parrallel or in series. Parrallel means you connect both set of speaker wires at the same reciever speaker taps. Series means you connect one speaker to your receiver then connect the other to the first speaker. If the resulting load is to low you can cause your amp to oscillate and even blow. If the resutlant impedance is to high, you frequency reponse curve will look like a roller coaster(Raul, thus is true with tube and ss)Courtesy of another Audiogoner, here is how you calculate it:12-01-04: Elgordo
For speakers in parrallel it's R1 X R2 divided by R1 + R2, where R is the speaker impedence. So two 8 ohm speakers would be 8X8=64 divided by 8+8=16 for an answer of 4 ohms. In series it's additive so two 8 ohm speakers would be 16 ohms.
Elgordo
From your description you speakers were hooked up in paralell. Doing the math in my head that yeilds 2.4 ohms. This could indeed cause some amps to oscillate. In sereies the answer would be 10 ohms. Too high, but probably will not damage your amp. Onkyo made some of the best receivers and maybe able to handle a low load. Check your manual.

I violated a rule: The right answer is usually the simplest one.