1ea. RadioShack 2054, PA Amp. (~$90.00). Use the 70V output and:
4ea. RadioShack 70VTR Transformers (~$60.00ttl) Run 14/2 lamp cord from Home Depot to: 4ea. RadioShack 1445 Outdoor Powerhorns (~$140.00ttl) I’m thinking the wire was somewhere around $160.00. Get 2ea. RadioShack Dynamic Microphones (~$30.00ttl) So your son (and his cousin) can yell at your daughter “You’re gone!!” when she knocks over a barrel running mid/high teens at age10. (a little brag there…sorry

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You'll also need about $30.00 in zip-ties.
You’ll need a $6.00 1/8”-to- RCA adapter cable so the kids can just bring out their iPod or portable CD player and plug them in and leave the nice stereo gear with the $50.00 per foot monster cable in the house where it should be.
The amp has 100Hz, 1kHz and 8kHz tone controls to add some lows and cut back the highs you’ll have with the horns.
No – It’s not stereo. But it’s a riding arena for God’s sake. Not a concert hall.
But that’s just me.
You guys with the high-powered calculators and more hi-tech audio system brains than I’ll ever have can probably come up with something really cool to put into a filthy dirty high humidity bug infested occasionally rodent visited (indoor, or not) environment, I’m sure.