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I calibrated my sound card then did a measurement while still in loopback and it comes out perfectly flat but it always has a large (like +10db) offset.

I expected it to come out like it does in the online help where it's near the soundcard calibration curve.

Another issue I have is when doing actual measurements software comes back saying I have something above 60db during the pre silence check.

My soundcard is pretty good, it's a USB TASCAM 144 made by Teac. The loopback test using RplusD says 66 S/N. If I remove the Mic it does pass the silence test.

The Mic is a Behringer ECM 8000. The TASCAM is supplying 48v phatom power (from the USB power).

Two other Mics (Radio Shack SPL) and a Professional Calibrated Genrad SPL meter all have this issue. I think I have something goofed up with my levels.

I went ahead with the measurement and there is lump bumpy mess just under 60db with a few bumps punching through. I did the SPL calibration etc. But I had to calibrate SPL to 95 to get it to match.

What is a reasonable noise floor in a living room of a small house not near a busy road. Nothing treated has windows etc. My Genrad says I have something at 50db in the low frequency range (somewhere between 20-250hz). The meter is good to 30db.