  Recently a proposal for the non-abelian effective D-brane action was given
through fourth order in alpha'. As the resulting expressions turned out to be
quite involved, some checks of this result are called for. In the present paper
we calculate the spectrum in the presence of constant magnetic background
fields and compare it to the string theoretical result. Apart from a small typo
in the original expression (the overall sign of thefourth order term), we
obtain perfect agreement. We discuss potential applications.
