Sweet Room

[alandbush]

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?

Ah, my apologies as you did mention the use of the high level signal.  Presumably using the REL crossover.
My suggestion is that you change to using the Devialet subwoofer pre out with the Devialet crossover set to 75hz.
I don't have a Devialet, so I expect to be corrected, but I presume the main speakers receive the high frequencies and the sub pre out outputs the low frequencies.  If so, the REL crossover will need to be 75hz or greater.

Otherwise, remove the sub and reposition the main speakers, or seating position, to produce a more even low frequency range.

That's the limit of my knowledge having neither a Devialet amp or subwoofer.

Ps - there must be another thread(s) on DevialetChat discussing the setup of a sub with the Devialet, if not on Devialets own website.