Go over to http://www.3daudioinc.com and ask over there. There are quite a few owners of both models there.

These mics are very different.

The 121 has what I would describe as a more "modern" sound. More midrange upfront (generally in the 1K area), less lows than the R84 and less extreme highs.

The R84 has a more mellow and relaxed feel, more low end than the 121, and slightly more air (above 10k) than the 121.

So it depends on what you want to hear...each one excels in different ways.

Nathan. I really like your website. What I like is the fact that you have taken the time to review products in their context. While all reviews can be summed up the same way at the end, yours are a step away from the norm.