extension speaker

[rosco]

hi guys;i've been playin some gigs locally lately with my ultrasound ds4 50 watt amp.sounds great[so i'm told anyway].some places i 've played though it just aint enough power .i need to beef this system up a little.just for vocals and guitar .i'd like to run a speaker off the amp .will it work?what do i need? i looked at the fishman solo amp but can't afford it[$1000].i play for about 50 or 60 people and have to stay under $300.thanks