oops that is an typo from my side i mean statically linked. As that the unit is/becomes part of the executeable. LGPL states that then "Alternatively, a statically linked library is allowed if either source code or linkable object files are provided.". So although you dynamically link to the mpg123 dll you also place lgpl code directly into your exe.
Also read term 3 of http://www.gnu.org/copyleft/lesser.html it is allowed to place a header file you use to dynamically link to the lgpl code under another license as long as it is does not contain code from the lgpl library. So to avoid the hasle i made the openal unit a dual license.