88dB is the speaker sensitivity. The 91dB is both speakers in the room thus the +3dB greater value.
Easy question about efficiency of speakers...
I've got Paradigm Studio 60's and they're listed as having an efficiency of 91db/w/m in a normal room and 88dB/W/m in anechoic conditions. So what is this speaker's efficiency, 91 or 88? Is a speaker's efficiency measure always given under anechoic conditions? Thanks,