Alternator going bad?

I have had an amplifier in my car with some subwoofers for about 6 months now. Whenever the radio is playing and I have everthing turned up, my radio loses power. Like it cuts off, then cuts on a second later. It goes off when I use power, like when I step on the brakes or use my signal. Is this the sign of the alternator going bad, or maybe the battery? Everthing is connected correctly and it has been doing this for a week now. The battery is about 3 months old also.

Might be your alternator is not high enough capacity. Does your "battery" light come on?

The battery light does not come on. Can it be the belt that goes to the alt. Somebody inspected my car and suggest that I should replace the belt becasue when it gets old, it tends to skip, and thats why I lose power to the radio.

The belt undoubtably needs to be in good shape for best capacity. Check the current draw of the alternator when everything is cranked. If its close to the rated capacity of the alternator, I would replace it with a high-capacity one.