Sweet Room

[PeppaPig]

I am not an expert, especially with regard to subwoofers, but reviewing your measurements suggests that your crossover would be better placed at 80hz. This may allow the sub to 'fill' the 'hole' in the 40-80hz range as well as removing the main speaker output below 40hz.  Of course, that all depends on the subs room placement and it's volume.

At least with REW, you can measure and see the effect that altering the crossover can have together with the effect of altering the volume of the sub.

Good luck.

At the moment the cross over is set the minimum 30Hz, it use REL high level input. If I set it to 80Hz , isn’t the sub bass section will bump up higher?

Again, I am not an expert, nor do I have a sub.

Perhaps the following image best describes what you want to achieve.

180hz crossover frequency example

The sub (blue plot) provides the low frequencies upto around 180hz, before rolling off and the main speakers (purple plot) roll in to provide the rest of the frequency range.

In your case, setting the crossover to around 75hz should cause the sub to provide the frequencies upto 75hz and the main speakers providing the rest of the frequency range.
Importantly, the crossover prevents the main speaker output around 20-40hz doubling up with the output of the sub.

Hi Alan, I used the REL high level input so the main speaker and subwoofer are both generating the bass at the same time. Anyone use high level input will face the same problem then?