If that works, you can make it permanent in your /etc/rc.conf:
allscreens_kbdflags="-b quiet.off"
Background:
After running kbdcontrol from an Xterm and seeing it print out an escape sequence, I realized that it is just trying to send a command to the terminal emulation in the console driver, and it might need to be sending something different depending on the console driver; then I looked for and found the answer specific to newcons: http://lists.freebsd.org/pipermail/freebsd-current/2014-April/049463.html
I don't have a system to test it on, but it appears that ALSA can provide mapping of output to the PC speaker. FYI, there are many pages out there that say this is a bad idea because the driver is intended as a "toy" and not for general use (it will burn a lot of CPU cycles), but that said, this should work:
# Load the PC speaker driver
sudo modprobe snd-pcsp
# Reload ALSA to find the new driver
sudo alsa force-reload
# You should now see pcsp (pcspeaker) as an ALSA output option
sudo aplay -l
Select the sound card as your output and have fun!
Best Answer
Have you tried executing the command
(try as normal user and as root)