Sound is Extremely Important
Sound is measured in bels. Each .3 increase in bels doubles the sound power output. It would take 16 air conditioners rated at 6.8 bels to have the same sound level as one air conditioner rated at 8 bels.
6.0 Bels - normal conversation
6.8 Bels - fan running at low speed
7.0 Bels - refrigerator
7.5 Bels - washing machine
8.4 Bels - garbage disposal
8.8 Bels - lawn mower
9.2 Bels - diesel truck at 10 feet
We would not recommend buying an air conditioning unit over 7.8 Bels.