The figure below depicts an amp running attenuated, to half power, into a pair of speakers. In this case each speaker is driven by only a quarter of the amplifier's full power, in stark contrast to the unattenuated, full power case, where each speaker is driven by half the amplifier's full power. As a result, the speaker cone breakup levels and tone are dramatically different.
The figure shows only two speakers, with the amp running at full power. But the key conclusion - that each of the two speakers sees only a quarter of the power generated by the amplifier - also holds in the case of the amp running at less than full power. It also holds for the much more general cases of pairs of identically rated speakers networks or more general amplifier loads.
