Should I upgrade from REL/510 subwoofer to REL/812 subwoofer?

I realize I am talking about old equipment from 25 years ago, but I think it is still appropriate.  We had a home theater room (roughly 20x20) with Linn speakers, Marantz power, and a 3 gun Runco projector.  For the bass we used a 15in downward firing Mirage 500 watt sub.  The was on the second story with wood subfloor.  We insulated the 'hell' out of all the walls (double offset studs) and floor.  The power of this system was unbelievable, while barely hearable downstairs in the family room.  This thing rivaled any movie theater in realism and effect.  Keep in mind though that this was for movies only as we had a separate system in the family room for 2 channel.

I have a reel S812 in 12.5X13  sized room and the S812 is incredible. 
I have it set so good that I never get room overload or a flabby bass

in have considered getting  2 S510s but 2 subs in a small room would be harder to accommodate.  Put one S812 in a corner and your done 

I think you would be happy

Good luck Willy-T

I have been a REL owner for 25 years. I have used the ST series Stadium III &Storm III. They lasted 24 years of great service. I currently have 3 S812’s. They do double duty for HT and 2ch on 2 independent systems. In most cases, 2 s510’s would be better than a single s810. The blend would be better and eliminating dead spots makes a huge difference in 2ch. The s812 will play louder and lower but it could overload the room. It’s difficult to get 1 sub no matter how big to completely disappear. My room is 15 x 20. It’s not huge but 1 s810 does. not completely disappear. Unfortunately, the room nodes win with only 1. I was lucky enough to attend Sumiko’s Master class for REL and Sonus Faber 25 years ago with John Hunter. To help with the complexity of speaker & subwoofer matching  to room size, They provided a chart which had multiple speaker brands and what REL or REL’s would match to the correct room size. On Rel’s website, they still have a modernized version of this chart. I would highly recommend that you check that out. You can email or call  their customer support. They have helped me many times over the last 20+ years. Happy Listening. 

I use two 510 subs with ML ESLs 11As in a space 16 x 14 which is linked to a much bigger room through double doors (kept open). Have them on springs sitting on sound absorbant floor panels, as the room has a  suspended wood floor, with large bass trap on rear wall.. Works really well clean textured bass no boom.

@willy-t 

Thanks.  My local AV guy knows my room well.  He’ll be at my home on Thursday swapping the S/510 for a new S/812.  He agreed with your assessment.

I’ll let all know how it sounds next weekend.

Thanks for everyone’s input.

Rich