i have solution for ur problem i m using a FM transmitter which is easily availabe in market. u can get it from any electronics TV, radio, tape repairing shop. it will cost u around 50-150 rs bring it and then open it and desolder microphone and connect a wire and a headphone pin (stereo pin) now plugin this sterio pin behind motherboard and listen your songs on any radio enabled mobile instrument (in my case i m using motorola c168) at 94MHz. I can listen songs from my PC anywher in my house within the range of 100-200m.
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if u need more coveragge area then u can use a 5v power supply or 9v cell inplace of two 1.5v pencil cell
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i forgot to tell u that u have to use 9v battery otherwise at 3v and 5v ur output of sound card at full volume will produce distortion because supply becomes less then the i/p becomes greater and output will be distorted and will hear lots of noise. even with 9v supply i m cannot gobeyond 80% of max volume so i will prefer to use 9v battery or u can try 12v reulated DC supply on ur own risk