Impedance Question

Your understanding is correct, you'd want two pairs of 8 ohm speakers.

wrong, the amps power usually doubles from 8 to 4 ohms hence 1 pair at 8 ohms or 2 pair at 4 ohms

Wait a minute.....

I'm not sure how the TFM15 is set up or wired internally so correct me if I'm wrong. But if the 15 is set up like any other receiver with an A/B speaker switch, having both sets of speakers active will result in having the loads of the speakers in parallel. If this is the case the amp with the two 4 ohm speaker sets will see 2 ohms at its output. Not good. I think you are correct to assume that the manual's reference to having two sets of 4 ohm speakers to hook up to the amp for A/B operation is incorrect. They probably meant 8 ohms which wired in parallel means a 4 ohm load.

As far as the lowering the impedence the amp sees gives increase power, yes it does. But only to a point. With the TFM 15 you can readily see that puts out more power when the ohms drop...100@8 vs. 140@4. But with the increased power comes increased current demands on the amp. If you run the amp with a 2 ohm load, you run the risk of overheating the amp or overstressing it. The specs on this amp only say the amp can deliver 200W into 2 ohms on a peak demand basis not on a continuous basis.

The TFM15 is a power amp with multi-speaker capability, not a receiver. That aside, your circuits analysis is spot on.

Jas,
Is the manual mentioning that the speakers will be wired in series? That's the only way the 4 ohm rating you mention makes sense to me.

lb,
Two pair of 8 ohm speakers in parallel is a 4 ohm load. I don't think you want to be wiring 2 pairs of 4 ohm in parallel.
BTW, few amps truly double in power going from 8 to 4 ohm loads. Sunfire is one the short list. Old Carvers are not.

spot on tour2ma

Thanks, but what then was wrong with F1's reply?

nothing at all , just winding him up, he was supposedly having such fun winding me up , i guess i just got all caught up in the fun

The fact that you gave a forum member a wrong answer on purpose speaks volumes as to your character or should I say lack of. That's ok though because now the entire forum sees you for who you truly are, a putz!!!

.

the right answer you gave was obvious, he knew it and went from there. what ever i said after that was immaterial.