None of the NUC products have an internal speaker; POST code beeps, etc. are all routed out through the audio subsystem and thus to external speakers/headphones that are plugged into the rear panel audio connector or to a TV or other device that is plugged into the HDMI connector.
This particular NUC DE3815TYBE has an internal amplified stereo speaker port. The header is yellow in colour.
The CMOS setup can enable or disable internal speakers.
Intel does not test and validate Intel® NUC on Linux; however we know that many Intel® NUC owners are successfully using different Linux distros. Hopefully some of those users will be able to help you here; otherwise you can check your Linux distro’s website for peer assistance with this issue.
After installing Lubuntu 14.04 the internal speaker works!
Probably the older kernel in Centos 5 does not support the newer Realtek ALC283 sound chip.
Still struggling with the serial ports at the moment....
After keying in the command below in Lubuntu 14.04,
stty -F /dev/ttyS4 <baud_rate> cs8 cread clocal
i am now able to talk to the 1st serial port!
echo Hello > /dev/ttyS4
just works! Wow!