HDMI sound

My son has an Acer laptop(win7) with HDMI port. However when connected to his TV, he gets the picture on the laptop duplicated on the TV but not the sound on TV. He relies on the sound from his laptop. The graphic card has no reference to sound or HDMI facilities.

Not all HDMI ports will support sound. Unless the specifications specifically state that sound can be output on over HDMI it is safe to assume this is not supported.

What's the model and which graphics chipset does it have?

Go into control panel > hardware and sound > sound > of the top of my head i can't remember specifically but poke around in there for an option to output sound to HDMI raather than audio card. Most recent laptops do work but older laptops don't as 5km very rightly says.

Or right click speaker icon in the tray and select "Playback devices"!

If running win vista/7:-

Click on the sound icon next to the clock and select "playback devices".

You should then see a speaker/headphone device and an HDMI output (if supported and correctly installed)

lol ... you beat me to it!