Adding a sub. - can i start with one?

@ozzy62 Whoa whoa whoa. That’s the reason I was asking what speakers the OP has, and what subs they are considering. The Audio Physic Tempo 25 goes down to 32hz. The Rel 510 goes down to 20hz, but at -6. I believe it’s more like 25hz or greater at -3db. The OP mentions missing some oomph and giving it some “kick in the sound”. That is desire for a very audible range, and it will effect the soundstage perception. Also, subs do more than just add bass, especially if they go low enough below 20hz - they clean up the rest of the soundstage and bring clarity to the rest of the frequency response. And yes, it is possible that one sub in a corner will bring more of that clarity on that side… affecting the imaging. This is why many people prefer two subs or more, for an even response through the room. 

@daveinpa To build on my last post above, you will need to decide on what you want the sub to do. Given you have over 700sqft (that’s over 20’x30’!) and really high vaulted ceilings, if you’re wanting guttural impact, the Rel 510 may not do it. This is not to say Rel is bad, but with their frequency response cutoff, they are designed for smaller spaces than yours and will mostly add only audible bass on the low frequencies.

The one other big benefit of subs is as I mention above. With proper integration and the ability to generate lower moving waves, subs can improve phasing issues and bring openness and clarity through the frequency spectrum and improve imaging such that everything “snaps in place”. For that to happen in your room, I believe you either need a sub that can go lower and is still “fast”, or you need a swarm like mentioned above.

Again, this not to say that one sub is not bad, but to reach your goal, you may end up choosing a different sub or path. I learned this the hard way and had to upgrade my subs almost immediately.

I love Rel, I really do. But they have limitations in larger spaces until you get to the 812 or higher, or unless you get many of them. For less, I really like the SVS SB4000 or 16 Ultra sealed subs, and if you play your cards right, you could get a pair used for $3K shipped. The SB4000 goes down to 19Hz at +/-3db, and you can integrate the sub on the fly from a mobile app in your listening chair… everything from volume, phase, crossover frequency, and parametric EQ. I’ve found being able to adjust phase by degree from the listening chair to be quite valuable. And if you do buy from SVS, they have a money back satisfaction guarantee.

I have also heard great sound with the swarm described above, but you may need more than four for a room your size.

In full transparency, I am a dealer, but I just started out and do not carry any subs in my lineup, so what I say is purely from experience and in no way trying to sell my inventory.

+1 lalitk

@daveinpa

Further to @blisshifi post about S/510 may not do it. My room is 15’d X 30’w and I am using a pair of Carbon Limited (same power as S/510) and they are more than adequate with plenty of power to spare. Ofcourse my listening environment and preferences may differ from you (my room is also acoustically treated). In any case, I highly recommend getting the second sub as soon as you can, any one sub in your large room is sure to leave you craving for more :-)

I would also encourage you to consult with REL and take their recommendation under consideration. REL offers 60 days home trial and free shipping to you and on returns.

And with SVS or any other sub, keep the connectivity in mind, does your current preamp or Integrated allows two subs integration. Getting two SVS for the price of one REL may seem like a right financial call but not the right decision, based on my experience.

I still contend that any single subwoofer that is doing subwoofer duty will not "unbalance" the soundstage. Now if you choose to run the xover up to 150-200 hz, all bets are off. If the sub is crossed over low enough, even running the volume too high will not localize the sub, it will only negatively affect the tonal balance.

That said, I choose to use two. In my opinion it gives a more even bass response, twice the output, and two only have to work 1/2 as hard. But you can get good results with only one.