How to avoid eco if we are not using headset?

Hello, I have a flash in CS$ and AS3 which use the camera and micro to comunicate 2 people.

All works correctly, but if we don't use a headset, and we are using the speakers of the PC and the webcammicro, this one receive the audio of the speakers and send the voice through the channel, and the person that are apeaking receives his own voice a couple seconds later.

There si some way to avoid eco for this scenario?

Thank you very much