What is +/- figure because if 10 then would at 30hz it's 10db down
Not sure, however this is spec on them. I run 4 of these (2 pairs) as main speakers in front room from a stereo amp. 4 together actually sounds better then just running 2.
https://europe.yamaha.com/en/products/audio_visual/speaker_systems/ns-f160/specs.html#product-tabs