The 116 volts is partiality from the utility, and partially the drop in your house wiring. Also any load on that side of the 240 line coming to your home, will pull it down. Central air will pull it down since it runs on 240, both sides, or phase legs. 114 volts at your service panel is minimum. The grade of outlet has nothing to do with it.
As far as sound goes, it's all dependent on the equipment in your system. Mine drops down that low when it's in the 90s, and everyone has their A/C on. I don't seem to notice any loss of sound quality. I run mostly low power too. If you have inefficient speakers, and a big amp, you may have some power loss. The sound would still depend on the system though.