Subwoofer Advice

Making deep bass accurately is very difficult because the laws of physics are stacked against us. Bass is also vague relative to midrange, it not as easily localized if at all and the timbre of bass instrument is determined by their contributions to the midrange. I cross to my high frequency transformer 500 Hz 2nd order and with everything else turned off you can still clearly make out most bass instruments. Synthesizers are the only exception I know of. A great subwoofer system is felt rather than heard. To get the maximum "feel" out of a subwoofer system you have to run it up to 80-100 Hz, painfully close to it becoming obviously audible. Doing so requires very steep slopes, above 10th order to minimize the subwoofer systems contribution to the midrange. Such steep slopes are only practical digitally. You can cross to the sub much lower and use a shallower slope, but you miss out on a lot of the feeling that goes with percussion and bass instruments. Anyone who has been to a live performance in a smaller Jazz club like the Blue Note or Birdland in NYC knows what I am talking about. Recreating that kind of bass in a residential environment takes a lot of power, a lot of subwoofer and digital equalization. Most systems are down by at least 6 dB, usually much more when they get down to 20 Hz. This is at the listening position, not one meter. To get realistic bass in most rooms requires adding at least 10 dB sloping up going down to 20 Hx. That requires 10 times the power! Another big problem occurs in the time domain. It is important that the signals from the various speakers arrive to you at the same time and in phase if that "feel" is to remain intact. You can move speakers around till you are blue in the face,you will never achieve the accuracy of a measurement microphone and digital delay capability. In many cases the correction is done by computer, even better. All this tech is now readily available and at a reasonable price. A $950 MiniDSP SHD Studio and two good quality DACs like Benchmark Media Systems will do the job for most systems. Such a set up will turn a run of the mill Mid Fi system into a stunning performer. Going up the ladder is Anthem and ARC followed by Trinnov and finally DEQX. 

@mijostyn That's really neat that you like going down rabbit holes in pursuit of what you consider perfection, but that doesn't sound like what the OP was asking about. 

I had an ML sub (dynamo 700), sold it. It was everything but subtle and easy to dial in. It was the big, unruly bully in the room

@mijostyn  I can't continue to look at the link you provide, it disappears on its own and goes to a rattle snake and other photos! Are your subs dual opposing one in each end? How much volume is in the boxes? What's that stack of lumber you have in your shop? Actually you have several stacks. Lumber is expensive unless you source your own like me. 

@grislybutter The Balanced Force series are much better. They are not perfect, but they are better than most. The enclosure creates distortion in two ways, shaking and vibrating. Both types occur around certain frequencies. Shaking is caused by unopposed driver forces. When the cone is pushed forward the enclosure is pushed backwards. This is completely cured in balanced force designs. Then there is vibration in the walls of the enclosure. This is not so easy to stop. It takes intelligent design, over construction and the right materials. The problem for commercial manufacturers is this is expensive to do and makes their products uncompetitive in the markets they serve. The Magico Q series subs cost $36K!  

@big_greg You are right, this is a diversion, but @navyachts problem has been successfully addressed and his interest has been diverted to the subwoofer question. I am nowhere near the most intelligent person on this website, but I have been using subs with ESLs since 1978 and building subs since 1987. Experience being the teacher that it is I feel qualified to deal with his situation. ESLs are like the most beautiful girl you wish you never met. It is easy to make them sound terrible putting additional requirements on associated equipment, particularly amplifiers and subwoofer systems.