I agree with ST that the best way to test mics/L1 is to take along the ToneMatch. In the above example when I swapped out the Neumann KMS-105 for the Sennheiser e935, I was using a ToneMatch set to the Neumann. The issues with feedback was not the fault of the L1, Neumann mic or ToneMatch. It was due to the limited stage space. The L1 was set directly next to me within 1 foot of my guitar and within three feet of my vocal mic. To add to the issue, the table of "customers" in front of me were VERY loud and we had to play at above normal volume to accommodate. It was the perfect storm for feedback issues. At this point, the best bet was to change mics to the e935.