O tópico a seguir pode ser pertinente:
Controle o volume de ambos os fones de ouvido e alto-falante do laptop (HP nc6000)
Simultaneously control the volume of both speakers and headphone simultaneously with the laptop's buttons
- Right click on the Volume control () applet
- Go in the Preferences menu
- Hold down the Ctrl key, and click on both entries Main volume and Headphone to make them both highlighted.
- Take note of the entry in the combo-box (mine is Intel 82801DB-ICH4 (Alsa mixer))
- Press Close
- Go in System -> Preferences -> Sound
- On the last combo-box, select the same entry seen earlier (ie Intel 82801DB-ICH4 (Alsa mixer))
- Hold down the Ctrl key, and click on both entries Main volume and Headphone to make them both highlighted.
- Press Close
From there, if you press the buttons on the laptop to increase or decrease the volume, it will now affect both the speakers and the headphones
Se isso não resolver o problema, dê uma olhada também neste tópico: Som do alto-falante e fone de ouvido - não é possível desativar o alto-falante