REL vs JL AUDIO

@tablejockey
I tested with 2 S812s (borrowed one from my local dealer) because you are absolutely correct 1 vs 2 would not have been a fair comparison.

@hilde45 and @jeffvegas
My experience too, my Rythmiks had better bass (much lower than the REL S812s) and I still say cleaner bass as well and there was certainly no delay with the servo (at least not audibly) perhaps due to the fact that I had so much more control over the setup of the Rythmiks than the RELs. (REL’s never did integrate as claimed) But I agree with jeffvegas that I think that the dynamics were a hair better with the RELs.

Always find these discussions interesting, there are so many factors which guide us to our solutions. The differences in equipment, the amount of money tied up in each component, and especially the room size and acoustics. So many variables... that is why I still prefer my brick and mortar dealers. -- wish there were more!

There is no question about this ….REL.  if you can play 2 and place them in the corners for best sound.  I have a pair of S2’s and they changed my sound significantly.

I personally like SVS. I thing they are well built, economical, and do a great job. 

@james633, bigger drivers of the same caliber are always going to sound better and that is science proven. There is a simple reason for it. As the cone excursion increases the suspension becomes progressively less linear. It gets stiffer until it can't move any farther. This distorts the waveform. Larger drivers do not have to move as far to move the same amount of air resulting in less distortion for the same output level. There is a limit however. As the cone gets larger it becomes more difficult to control and in many instances starts to wobble. You can see it happen with a strobe. The largest anyone has to go in a home installation is 15" If more power is needed the go to multiple drivers which accomplishes the same thin as larger drivers, shorter excursions. With the right size drivers servos are not needed at all. It is easy to keep distortion under 0.5%.

There are issues with the use of subwoofers that manufacturers won't mention primarily because they can't deal with them or are afraid that the increase in price will knock them out of the market. 
The first is the use of a high pass filter or rather a complete two way crossover. Taking the bass out of the main speaker dramatically lowers distortion in low frequency drivers that operate well into the mid range. You can tailor the response curve of the main speakers and subwoofers to match perfectly and you can take the crossover point up higher without difficulty. Next is a critical issue that they never mention. The impulse from the subwoofers and the main speakers has to reach your ears at the same time. You want to listen to one bass drum not two bass drums. This can not easily be achieved by positioning the subs. The problem is that subwoofers are most efficient in corners and against walls, up to 6 dB more efficient requiring much less power which is vitally important if you are using DSP correction. Most people position their main speakers away from the wall placing the subwoofers 3 to5 feet behind the main speakers. That is a 0.3 to 0.5 millisecond group delay. The easiest way to fix this problem is to digitally delay the signal going to the main speakers. Phasing and time correction are impossible to do accurately by ear but you can measure them with a $300 microphone/measurement program or with a comprehensive room control system. If you want to fix the group delay by moving the subwoofers or speakers then all you need is the measurement microphone. You will just have to accept the fact that your system will not be as efficient as it could be but if you do not have digital facilities this is the only way you can do it. Comprehensive room control preamps with bass management programs are the best way to go. New units are coming along all the time and some of them are not very expensive. MiniDSP, DEQX, Anthem and Trinnov are a few. 

There is no commercially made subwoofer that will provide state of the art bass out of the box. The system I describe above will out perform any subwoofer named so far in this thread and not by a little. I will not buy any more commercially made subwoofers. There is only one that meets my requirements and it is $36,000.00. I would need four of them 🤢 Discounting my labor I can do pretty much the same thing for $15,000.00 in drivers, amps and enclosure materials. 

I have no relationship to Audio Kinesis but I think most here would be better off buying their swarm system.  

If you have one of the above subwoofers you can do your main speakers a favor by soldering capacitors in series with the inputs of your amplifier.
The value is calculated with this equation Fc = 1/2piRC or C = 1/Fc2piR Fc= cut off frequency, R=input impedance of amplifier, C= capacitance in Farads. So if your amps input impedance is 10K ohms and you want a cutoff frequency of 100 Hz  C = 160 nF.   You can get the caps from Digikey. I forgot to mention that this is a 6 dB/octave filter.

I wouldn't advise either. 

If I were you, I'd give a good look at SVS.