Unless you got an HDMI to VGA plus audio converter you wouldn't get sound from your monitor unless your free to air box has an analog audio output that you can connect to the monitor.
Your post cut off because you tried to type it in the title not the main body of the post. You need to edit it. When you do, put in exactly what devices you are using, not just "tft screen" or "air box" since there are hundreds of different ones.
Unless you got an HDMI to VGA plus audio converter you wouldn't get sound from your monitor unless your free to air box has an analog audio output that you can connect to the monitor.