Reduce the volume?

My problem is… I import two sound files and give the linkage name snd1 and snd2.

In the first key frame I add this

sound1 = new Sound();
sound2 = new Sound();
sound1.attachSound(“snd1”);
sound2.attachSound(“snd2”);
sound1.start(0, 5);
sound2.start(0, 5);

And also I create a button for control the sound

Inside the button

on(rollOver){
sound1.setVolume(25);
}

on(rollOut){
sound1.setVolume(100);
}

The correct out put is when I rollover the button… sound1 volume is reduce to 25. but the both sound1 and sound2 volume is reduce…. it reduce the master volume. How it is happen. give me a solution or if u have any deferent way to control it please tell about that….