Tone Generator firefly

Hi everybody, I'm approacching to firefly and arduino. I did a lot of examples using LEDs and now I would like to use also the "AUDIO commands". I plugged the speaker in the board and then I used the Note to frequency command to get the frequency from the note, but when I try to connect the output of this command to the Digital pin 8, i can't hear any sound. Where's the problem?

Thanks for your help.