Stream audio from macbook pro to tv

I'm using a MacBook Pro 8.2 and want to stream video to à Sony Bravia TV. I've connected them with à cable from the Thunderbolt port to the HDMI port on the TV. I get the video images but no sound. Is there à way to do this or do I need à separate audio cable?

There is great risk of confusion since I am seeing the words in Swedish and it is sometimes difficult to tell what the translation should be, but here goes:
In the System Report there is only one topic with the word sound: "Sound (built-in)"
Under that topic it says "Intel HD Sound" and I can choose a nummer of options, but only one for "Speakers" and it says "Connection: internal"
There is also an option for "HDMI/DisplayPort" which says "Connection: screen" (or monitor)