Yes there is. In my experience the KSM is a bit brighter sounding. Its kind of more of a flattering mic which can be a great thing, or could also be a little much, but that really depends on the source signal, the preamp, and what your own ears enjoy. The sm81 is much more "neutral" sounding to me. It captures more of what is really there and doesn't do anything to help you out much. In the end, which mic to use really depends on a combination of other factors.