My problem is that on my system HP/DC7900, I have always the same sound like on my sound card on the internal PC speaker. I check all settings and don't find an option to disable the internal PC speaker.
Is there any solution for this problem?
You can temporarily disable the internal speaker with this command:
Or to permanently disable it create a new file in /etc/modprobe.d/ called something like blacklist-pcspkr.conf or whatever you'll recognize. Add the following line to that file:
Of course, that will completely disable the speaker while the OS is running, so things like command line typos that make it beep as feedback won't happen either (BIOS errors will still work as the OS won't have disabled it by that point). If you want it to beep when it normally would on certain errors, but not to play music through it, then that will require some further troubleshooting into your sound settings to see why everything is playing through that output.