He was able to get some help in the Adafruit Forums to solve the design challenges:
I am working on a project which I expect to power through a wall socket. I am using an Arduino Uno with a Wave Shield stacked on top. The Wave Shield will run through the Stereo 3.7W Class D audio amp and playback will be controlled through presses of a single button.
And from the project description:
The first outdoor installation of the Stranger Reduction Zone occupies a corner near the main entrance to the Plaza of the Rockies in Colorado Springs. It is part of the city’s 15th Annual Art on the Streets outdoor art competition and year long exhibition. You can find it on South Tejon Street between Colorado and Vermijo Avenues.
Featured Adafruit Product!
Adafruit Wave Shield for Arduino Kit – v1.1: Adding quality audio to an electronic project is surprisingly difficult. Here is a shield for Arduinos that solves this problem. It can play up to 22KHz, 12bit uncompressed audio files of any length. It’s low cost, available as an easy-to-make kit. It has an onboard DAC, filter and op-amp for high quality output. Audio files are read off of an SD/MMC card, which are available at nearly any store. Volume can be controlled with the onboard thumbwheel potentiometer. This shield is a kit, and comes with all parts you need to build it. (read more)