Does a REL subwoofer make the speakers' job easier?

In answer to the original question, a sub can make the main speaker job easier if it is crossed over with high and low pass filters (full crossover). This way the mains are not receiving bass frequencies and can deliver cleaner upper bass and midrange, depending on the main speaker configuration (2way, 3way)..

But the issue of phase and delay has been mentioned. Phase is not really proper time alignment, it is really just putting a late signal in phase, in fact usually making it even later.

Also be aware every sub probably has a few ms latency due to the electronics, cabinet design and impulse response of a large driver). I gather manufacturers are not eager to share this info. To compensate, it is necessary to delay the mains, not the sub. I have done this. One of my subs has 12ms latency, but it is still very nimble responsiveness (it is not sluggish when time aligned correctly)

In my system, there was quite noticeable improvement from even a 6ms adjustment, 12ms is obvious to me and frankly messes with the music timing let alone the acoustic interactions/cancellations.

With all this in mind, the approach promoted by REL to use high level inputs seems fundamentally flawed. Be wary of the marketing the REL dealers use.

REL subs are support for lower end extension and do not provide a crossover to your main speaks, as others here have clarified. I think there is more debate on two vs. one sub and placement. Hearing where bass comes from is the issue -- it's impossible below certain frequencies, which are the frequencies the sub produces. REL recommends putting a sub at the place in the room where it maximizes low end extension at your seat. Hopefully that spot works in one's room. My experience is like @tantra4 in terms of integrating. The phase switch has always been adequate. Bass does change if you move your seat around the room in and out of of nodes. So you can play with seating position as well. Have fun experimenting!

@johnson0134

Once you have added the dual subs to your system, It would be helpful, for the benefit of all,  if you could post your first-hand experience of adding the REL subwoofers to your system and how it changed the sound for you and any recommendations!

Rel hi level is incredible. Using Rel for over 22 years still have my Rel stentor 3,s with Extremas. In bedroom using two real 9x with Tannoy mini,s incredible

+1 @hilde45

It continues to blow my mind that big sub manufacturers like Kef and Rel don’t even have a phase dial for exact phase matching. Only two opposite settings? It’s simply bizarre to me. Apparently there’s consensus out there there only the tiniest percentage of people are actually aware of how impactful precise phase adjustment is for integration with loudspeakers, having learned through experience with using precision phase adjustments.