You are to be used outdoors, 700 square meters, the site is relatively large it, portable amplifiers may not be so suitable Oh, because the sound will be very small it, I'm home this side of the square dance with the amplifier is the Dessen E17, this is a multimedia wireless amplifiers, power is relatively large, you can meet the use of the 800 square meters it, there is a head-worn, hand-held, lapel clip can be selected it, my is the The head-worn Oh, quite good.
I hope it works for you!