[Otto]

Hi logan,

The "headroom" measurement that REW is providing is that of the input of your PC clipping. So, it makes sense if it gets smaller when two subs are playing, since they are louder and pushing you closer to clipping.

Have you ever used a mic and set levels based on a needle or meter moving? The louder you yell into that mic, the less headroom you have going into that system from the mic. And the louder you yell, the more you move that needle into the red. Same thing with the colors of the meter in REW.

It's not measuring the headroom available in your stereo system or to your subs.

Have a good night.