Playing WAV file from Arduino Uno using Ethernet R3 Shield
Your Arduino UNO won't play any wave file the way you're expecting. There's not enough processing power to do that.
In order to play audio using small MCUs such as AVR (or PIC for example) you must use the BTC algorithm. Please, check this out : http://www.radanpro.com/Radan2400/mikrokontroleri/How%20to%20make%20sound%20with%20a%20PIC%20chip.htm
and download the software which can convert your wave file into an array which can be then played by Arduino using a BTC algorithm. Schematics on how to place reistors and speakers to match impedance are provided and suggested on the software as well.