by msmpe » Mon Jun 20, 2011 10:58 pm
There's a couple ways to do it. Run the speakers in series, that will add up to 12 ohms, which is not what your amp wants to "see" so you'll be down on volume. I've never liked the results.
You could hook em up in parallel, but in parallel the impedance the amps sees is 4x8/4+8=2.7 poof! But you could then run a 5 ohm resistance in series 2.7+5=7.7, close enough. The resistance should be non-inductive, PatrsEx has some non-inductive speaker resistors, make sure the wattage of the resistors is as high as your amp or almost as much. Maybe it sounds OK, maybe not! I do like 2 pairs of speakers, but it depends on the tube amp.
One last possibility. This one comes from a little book written in 1963 titled HiFi Projects for the Hobbyist by Leonard Feldman. In chapter 6 he describes a way to hook up two speakers of differnt impedances. He hooks the postive of the 4 ohm speaker to the positive of the 4 ohm tap on the OPT and the respective same for the 8 ohm speaker, with the speaker negatives connected in common to the negative/common on the OPT. Feldman also shows how to connect a 3-way switch to selct A, B, or A+B. Quoting from the text, "it is true that the prescence of a speaker across the other tap of the output transformer alters the total impedance of the transfomer slightly, the effect is more negligible than would be the case if the two speakers were simply wired in parallel."
Does anyone know how to calculate what the impedance is that the amp sees hooked up this way?
8>) Mike
If there's no sound in a vacuum, where'd the music come from?