both speaker and headphone sound can be heard once headphone connected

both speaker and headphone sound can be heard once headphone is connected

What type of headphone? USB or with a standard TRS plug?

Also, some audio systems have option to either mute speakers when headset is plugged in or to not mute the speakers when the headset is plugged in. Check your sound control for this option.

Please fill in the "My Computer" specs as all we can do is offer general suggestions without it.