1) If speakers are not built in, you can't get sound from it. Well, you could drop it and it would make a sound, but that's not what you want. I can't find the specific model, can you provide a link? I suspect that you are going to need separate speakers, but if you provide a link I'll check.
2) What do you mean that you are connecting the monitor to a modem? Usually, they are connected to your graphics card, yes?