Impedance Setting on Amp


Standard Member

I am bi-wiring a pair of Kef Cresta 2s to a Yamaha DSP-A5 amp. I'm a little confused as to what speaker impedance setting to use? does the bi-wiring affect this?

the speakers are rated at 8Ω each.

the two options are in the attached picture, can anyone help?




Well-known Member
Use the option with everything at 8 ohms (so the switch on the right hand side).

Bi-wiring does affect it - if the whole speaker is rated at 8, then splitting it in two will mean that each part will be higher impedance. (you could guess 16 ohms each, but in reality, the LF one will probably be lower than the HF).

And as you're bi-wiring, I guess you'll be using the 'A+B' option from the amp.

That's a little odd actually... looking at the numbers, it looks like the A and B outputs are just duplicate outputs from the same amp circuit. Usually, AVRs actually give you two amp circuits. you're still fine with it in that mode - that's just a little interest point.


Distinguished Member
The only effect biwiring has on the impedance is the minimal impedance difference caused by doubling the wire's cross-sectional area - impedance being a function of frequency. Unless you're using ludicrously long and thin wire, you can ignore it, and if you are using such inadequate cabling, you have bigger problems to solve than this.

It is only with biamping that you need to consider the impedance curve (impedance vs frequency), to determine the impedance presented to the independent amplifier channels when you partition by frequency at the crossover. Most speakers present a reasonably consistent impedance over its usable frequency range, which is how why it is only necessary to quote a single numeric value for the instrinsically frequency-dependent measure. My Spires are an example of a speaker which isn't.

The value to select on the amplifier is the value printed in the speaker manual (here the position on the right).
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