Impedance - help urgently required by novice

I have recently got hold of an Arcam A85 to connect to my Mission speakers.

In the instruction booklet it states:

You can connect one or two pairs of speakers to your amplifier, provided each pair is rated between 8-16 ohms. If one or both pairs have an impedance of less than 8 ohms, the combined load on the amplifier falls below 4 ohms and could cause an overload.

Forgive my ignorance, but does this relate only to the use of two pairs of speakers.

The reason I ask is that the single set of Mission speakers I intend to use have an impedance of 6 ohms. The speakers I would one day like to buy are Monitor Audio S8s, which also have an impedance of 6 ohms.

In short, can I use a single pair of 6 ohm speakers with an Arcam Diva A85?

I'd really appreciate your help.

 

Yes, it only relates to two pairs of speakers.

Arcam/Mission is usually a great combination (voice of experience)

 

Yes, you can. In fact 6 ohms is about ideal to get the best volume -v- strain on the amp. I agree, the wording in the manual is not clear - as you state 2 pairs combined should not go below 4 ohms. This could be, say, 2 x 8 ohm pairs, or various other combinations that are unusual anyway

with your 6 ohms, you can safely connect another pair 12 ohms [or higher] to each L and R output.

 

Many thanks, Chris and Graham,for your prompt replies. Much appreciated.

 

In short yes you can use these speakers in perfect safety.

Impedance is rarely if ever a perfect 6 or 8 ohms or any other figure. If you plot a curve of impedance against frequency for the speakers, it likely will have peaks and troughs and will be non linear. Therefore the factor that determines whether you can have one or two pairs of speakers connected is if the amplifier output stage can drive the extra current without overoading the devices. The A85 can obviously not drive 2 sets of speakers if they have a nominal impedance of <8 ohms each as this may, depending on volume, and impedance curves, overload the current driving capacity of the output devices. In practice this amplifier, probably, will have overload protection but I don't know for sure.

The theory behinfd this is that 2 speakers in parallel will show half the impedance to the amplifer. e.g. 2 sets of 8 ohm speakers will show a nominal impedance of 4 ohms to the amplifier. This is OK. 2 sets of 4 ohm speakers will show a nominal impedance of 2 ohm to the amplifier. For the A85 this is not ok.

Kevin