At 07:15 AM 1/29/2003, Eric Zeno wrote:
>The impedance between 4 and 8 ohm to an audio amp,
>is almost insignificant.  Unlike if you where feeding this in
>to a 1000 ohm load.  Wiring 2 speaker on the same amp
>has the same effect as a difference between 4 and 8 ohm
>impedance. So, don't be concerned unless your trying
>something fancy.
>                                                       Eric

These are power circuits, and we're talking about a 2:1 ratio of impedance,
so it's not entirely trivial.  If you're not running at high outputs it no
doubt doesn't matter -- but if the source and load impedances are not equal
some of the power will get reflected back into the source, which
undoubtedly will cause a certain (small) amount of distortion depending
somewhat on the length of your speaker wires.  Also, if the load impedance
is lower than the amplifier is rated to handle (and the ratings vary and so
do the safety margins) the output stage of the amplifier can overheat.  In
a transistor amp the output will overheat (and in case of an actual short
circuit may instantly suicide*) when the load impedance is too low.  In a
tube amp the output transformers will overheat if load impedance is too
high (not sure what happens if it's too low, maybe nothing).

Some amplifiers but the speakers in parallel when you run two sets --
reduces (eliminates?) some possible distortion from interaction between the
speakers, but means that the load impedance is less -- two ohms for two
four-ohm speakers, 2 2/3 ohms for a four and an eight, four ohms for a pair
of eights.  Others put them in series, which means no overload problem but
possible distortion.  It's easy to tell, just hit the B speaker button with
no speakers connected -- if the A speakers keep playing they're in
parallel, if they go silent they're in series.

*The ability of transistors to supply almost infinite current into a short
circuit leads to the following rueful ditty:  "Transistors fused against
the worst, protect the fuse by blowing first!"

david

--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"