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@donavabdear , My system is really very simple. I have a digital preamp that takes digital inputs from a universal disc player, the TV box and a Lynx Hilo. Connected to the Hilo is my phono stage, an Apple Mini, the Apple TV box and the Sonos connect. The Connect is hooked up to a very powerful router along with the Apple TV box. All the processing is done in digital. The processor is managed by a PC not the Apple mini which just plays music from a 6 TB hard drive. The processor has 4 DAC channels that power two speaker amps and two sub amps. The Hilo is a studio ADC/DAC mixer of amazing capability. There is nothing on the consumer market like it. As soon as it is released I will be getting a DEQX Pre 8, a full digital preamp with Room control, EQ and a 4 way crossover. It have 8 DAC channels. I may add ribbon tweeters to my ESLs.

As far as subwoofer enclosures are concerned a square or rectangular box is the worst design. The air within the enclosure is a spring. In the old days this was called acoustic suspension and like any suspension it has a resonance point. There are no standing waves within the enclosure. The enclosure wants to expand and collapse. Each size panel now has it's own resonance point as they flex and that resonance point can be up in the midrange!  Put your hand on the enclosure while the sub is handling heavy bass 30 Hz at 90 dB.  First put your hand on a corner. The vibration you feel there is the enclosure moving back and forth from the Newtonian forces generated by the driver. Next put your hand in the middle of one of the sides. Here you feel a combination of the enclosure moving back and forth along with it expanding and contracting.  A cylindrical enclosure is inherently stiffer and will be very resistant to compression and expansion. It will still move back and forth to Newtonian forces unless you mount an identical driver on the opposite side and drive it in phase with the front driver. This is called a balanced force design. You would have to double the enclosure volume resulting in a larger subwoofer but with the right modern subwoofer drivers you could still limit the size to 2 cubic feet excluding the volume of the drivers about another cubic foot. 3 cubic feet is not horrendously large. 

@kota1 , the absolute best place for a sub woofer is on the floor in a corner. The next best place is on the floor against a wall. You are sort of horn loading the sub. The only problem is time alignment which can be easily taken care of digitally. You can see the group delay with a good measurement system but in order to correct it you need DSP.   

Hence bracing, The large the panel dimensions, the greater the bracing. A superior shape is of little benefit if we cannot manufacture it, added shipping costs ameliorate the benefit, or it causes difficult in use for the customer. FEA allows easy and quick analysis of designs.

Spoken like a HT guy.

I thought the trunk was the bast place for a subwoofer.

the absolute best place for a sub woofer is on the floor in a corner. The next best place is on the floor against a wall. You are sort of horn loading the sub. The only problem is time alignment which can be easily taken care of digitally. You can see the group delay with a good measurement system but in order to correct it you need DSP.   

@thespeakerdude wrote:

Hence bracing, The large the panel dimensions, the greater the bracing. A superior shape is of little benefit if we cannot manufacture it, added shipping costs ameliorate the benefit, or it causes difficult in use for the customer. ...

Hence DIY; in principle every design, shape and size (and weight) can be pursued. I’ve gone the horn route with subs where the horn "innards" are elaborate bracings. Large behemoths, but constructed in 13-ply BB with CNC-cut and interlocked panels they’re very sturdy. Further damping can be applied and accommodated as one deems necessary.

Distortion isn’t only cabinet vibrations but as well mechanically induced noise from the direct radiating and exposed woofer(s) during high excursions. Horn-loaded woofer cones, while concealed inside the horn, move very little for a given SPL, potentially both due to high efficiency and the way the woofer cone can have minimum excursion at the tune (via Tapped Horns; not the more traditional Front Loaded Horns where the woofer is usually placed in a sealed chamber). Avoiding mechanically induced noise here is not trivial.

Very few audiophiles have been "exposed" to the sound of horn-loaded subs (or their variants), not least for the reasons you outline as a MFR, which is a shame, because they deliver a very smooth, enveloping and effortless bass reproduction when carefully implemented - certainly audiophile qualities in bass reproduction to aspire to. Their ability to produce truly prodigious SPL’s is part of their perceived prowess here (and so not only about loudness per se), because significant headroom equates into cleaner/less distorted and more relaxed bass.