Listen to headphones excluding internal laptop audio

[Pido17]

Hi! This is my problem:
When i insert the headphones i listen to music both from headphones and from the laptop internal audio. When i first installed ubuntu on my laptop this matter didn't happen. Then i installed ardour2 and it occurred. So i removed ardour and the problem disappeared... now i've installed other musica software (audacity, zynaddsubfx....) and the problem came out again. Removing all my audio software i can't solve the problem. How can i listen to headphone excluding laptop music?
Thx and forgive me for the bad english..
P17

[Pido17]

I read trough many 3d but nothing.. many other have similar problem. How can i listen only from headphones and not from the pc?