OSX Sound Card Issue?

[readthis13]

As of last week, I was running the latest version of OSX and REW. I have yet to download the latest beta. However, I get a massive drop off at 40hz when measuring sweep tones 10-250hz using a calibrated UMIK. When tested on a Win10 laptop, it measures just fine. Nothing has worked to solve this, and I'm hoping there's a known solution.

 

[John Mulcahy]

Does the mac have an internal mic? There have been reports of macbooks with internal mics capturing audio from the internal mic instead of the selected UMIK.