In Lubuntu 18.04.1 my speaker volume control hot keys did not work. In trying to find a way to edit the lubuntu-rc.xml file I found a GUI approach to achieving the same results as answered by @spucktek and @Alexander Mordovskiy. The solution is still to change the XF86Audio command lines from "-q sset" to "-D pulse sset".
To modify the lubuntu-rc.xml file in the GUI
-> select "Menu" from the desktop panel, my menu button is on the bottom,
-> then "Preferences" -> "Set Up Hot Keys".
The LXHotkey panel opens up. There are two tabs at the top of the panel, Actions
-> Select the Programs tab.
Find the "XF86AudioRaiseVolume" asset under the Hotkey 1 column.
-> doubleclick 'XF86AudioRaiseVolume' and a small edit panel opens.
-> in command line field change the "amixer -q sset Master 3%+ unmute" line
from 'amixer -q sset' to "amixer -D pulse sset"
The command line should now read "amixer -D pulse sset Master 3%+ unmute"
-> click the [check button] at the top of the panel to apply the changes.
Repeat for entries "XF86AudioLowerVolume" and "XF86AudioMute".
Once you're finished
-> save your changes by clicking the "folder" icon button located directly below the "Edit" menu.
Hopefully a noob like myself will find this helpful.