As others have mentioned, this is not what's happening. Even if it was, this was a high pass filter (letting everything above 30 Hz pass), not a low pass filter. But again, this is not how it works.
It might just be your sub implementing this high pass filter. Are RSL still in business? I don't find any website. Which exact model do you have?
Nothing against HomeCurve (on iOS and iPadOS devices) but on your Macbook you should rather be using Room Equalization Wizard.
REW is free software for room acoustic measurement, loudspeaker measurement and audio device measurement and analysis
www.roomeqwizard.com