Authorized Boogie said:
That is not a safe mismatch, and not recommended.
Really? Do tell why?
What he's doing is safe. It's even stated as such in the MkIV manual!
More than a few of us have hooked up two 8phm speakers this way on the Mark series amps.
One speaker would be a little louder than the other. That may be why he likes it.
Power tubes may wear a bit quicker but if it gives him the tone and sound he likes then so what.
Right from the MkIV Manual (bold is mine):
Speaker jacks for both 8 ohm and 4 ohm loads are provided.
Two 4 ohm jacks are provided and should be used when you wish to run two 8 ohm speakers
or cabinets. (This is because two 8 ohm loads connected in parallel present a combined load
to the amplifier of 4 ohms.) Speaker mis-matching is not a cause for great concern - unless the
combined load is considerably less than the rated impedance. If, for example, you run two 4
ohm cabinets - each plugged into a 4 ohm jack - the amplifier would “see” 2 ohms as the total
load. And while this will not cause immediate damage, it will result in shortened power tube
life. Mis-matching on the high side is always preferable, if you have no choice
And it's equally safe according to the MKIII Manual as well as the MkIIC Manual
MKIII manual states:
SPEAKERS
One 8-ohm and two 4-ohm jacks are provided. The Boogie is not very sensitive to speaker mismatches and will not be damaged by
them except that very low ohmage loads will cause the power tubes to wear out faster.
MkIIC Manual states:
Three speaker jacks are provided: one 8-ohm and two 4-ohm.
If two 8-ohm speakers are used, plug each one into a 4-ohm jack for proper balance.
But you may also try other combinations if you want one speaker slightly louder
or happen to prefer the tone caused by a slight mismatch; it will do no harm to the amplifier.
and
Again, no harm can be done to the amplifier by mismatched speaker loads and we encourage you to experiment, if you want, with various combinations.
