"Musical" subwoofers? Advice please on comparing JL subs

Tuberculin,
This might be a better read to explain Class D vs. Class A or A/b
https://en.wikipedia.org/wiki/Class-D_amplifier

You can read how Class D is not a ’digital’ amplifier. It’s simply a full on or full off output device vs. a full on all the time device. Theoretically it can achieve 100 percent efficiency, but with the available devices it is not that high obviously, more like 90 plus percent. Class A amps have a theoretical efficiency top of 50% and as the article states often they don’t even hit 20%. But Class A amps make for fabulous winter time axillary home heaters or summer time A/C test appliances. Class D amplifiers using sophisticated feedback design and equally sophisticated power supply design not only deliver incredibly high output power with very little losses going into heat, but they move any distortion (by design) out of audible ranges. This is why a nicely designed Class D audio amp can be so incredibly smooth, powerful and not very warm to the touch with amazingly low power consumption in the idle mode. I think that my 2000 watt per channel M1’s draw only 3 watts in standby and 13 watts when in full on operation at idle.
I tried to get a copy of the schematic of the M1 from Anthem as a buddy of mine who is an excellent ex-Bell Labs electrical design engineer wanted to study what they employed. Anthem told me that they do not supply technical design data on this amp to anyone as it is extremely proprietary. The guy at Anthem told me that they invested over $5 Million dollars in the R/D engineering of the circuits and they don’t wish to share it with any competitors. I suppose I fully understand this. B&O on the other hand developed their Class D ICE modules for general distribution to manufacturers who wanted a quick and easy way to build Class D amps at very reasonable cost. This is why most amps in Class D on the market are using ICE power modules and why they are great for Sub woofers where high frequency harshness is not an issue, but powerful low distortion Bass frequencies work well.
I did have the opportunity to test and evaluate the Parasound Zonemaster Class D amp. They sent me one to try against the A51 and the M1’s. The Zonemaster is a very nice compact, 600 watt per channel amp. It actually plays very well, but for my ears, it had that well known high frequency harshness due to the inexpensive ICE modules. But it only costs $1200 dollars for a 2 channel 600 watt per channel amp! I told the guys at Parasound that as much as I enjoyed playing with the amp, it was not in my opinion well suited for a very high end audio system with high resolution speakers. I said it was absolutely perfect as an entry level amp for people just getting started and on a budget, or for college kids who want a lot of power in their dorm rooms and who have to move around often as its so light and compact/easy to move; or as an amp in a home theater requiring more channels to drive surrounds or rear speakers.  People using lower cost speakers which are not going to be extremely resolving in the upper frequencies might not even hear any harshness. They got a laugh out of that and said I had actually hit it right on the mark in terms of who their intended market was; so they were very pleased that I was in agreement. They never expected it to be competitive against the likes of the M1’s. But the Zonemaster blew away the A51 Halo in lower end, lower/mid grunt, that thing has some balls. It just was not as smooth in the upper mids/upper range as the A51. A $1200 Zonemaster vs. the $5000 A51 did pretty decently overall though. If I was back in college in my dorm room which was set up like a party/disco club, I would have been the place to be hanging out had I owned the Zonemaster back then vs. my old tube amp. But then again the speakers probably would not have made it through a weekend.

When it comes to high end amps, I think from what I am told the Bryston 28B3 monoblocks at $30K are about as good as it gets. I chatted at length with Ian at Axiom about the 28B3’s vs. the M1’s. He has heard both quite a bit and he told me that they are both top of the line, but he likes the massive reserve power of the 28B3’s and those are his go to amps. I of course pointed out that he is talking in terms of money being no object and he agreed. I asked if he was doing a value comparison, that is the $30K 28B3’s vs. the $7K M1’s, what would he do.... he said the M1’s would always be his normal second choice, but when I put it that way, he’d definitely go with M1’s; they are very close in performance. So there you have it; a well designed Class D amp pair against the some of the best in linear high dollar monoblocks is right in the running. And I am not heating the house with it or paying large utility bills.

As far as a sub amp goes (or run up to ~1kHz) the Class D-based Crown K2 is as good as any I've heard. When bridged it's supposedly a fine all-round amp not restricted to subs/lower to central midrange prowess only. 

As great stand-alone all-round amps costing less than a fortune the Crown Studio Reference I/II (now discontinued) and MC² Audio S800/1400 are highly recommended. Money placed where it matters. 

Slim, I read the Wikipedia thing long ago. I have been familiarizing myself with the digital amps for a long time. I wanted to see what all the hype was about. I have a degree in electronics and spent most of my career in digital. No, I'm not an amp designer, but I understood Class A and A/B over half a century ago.You can't convince me bits ain't bits. Nothing you say can sway me. You're talking spending new car money for amps. Sorry, even the cheap ones are off the table. Not class A or A/B.

I really don't care about efficiency, heat or any of the "benefits" of Class D. Full on and full off is bits. Bits are bits. Bits are digital. Plus they have switching power supplies as well. Enjoy your Class D's and spend another 50K to 100K on equipment. If you got it  spend it.
Peace, out.

Ah, but there is where you are wrong, the good ones do not have switching power supplies, that was precisely my entire point.   And the operational state of a solid state device is not a computer bit.  But that's OK, I really like the Class D and others should try them too.

Here's some of my thoughts on rooms and subs.

Right now, I'm figuring out the best location for my system in my room. It's about time. My room is 14.5' x 19.5' x 8' high. I listen across the 14.5" dimension out of necessity. I am using a readily available Room Analyzer package. This hardware/sofware generates audio sweeps, records the sound pressure with a mic, and calculates freq response, reverberation time, room modes, phasing and delay times. I am using a DIY sub. It has a 10" Scanspeak woofer in an acoustic suspension design. The main speakers are B&W 805s on the stands provided by B&W.

With the listening position against the wall opposite the speakers and the sub to the left of the left speaker, I've found several frequencies (40, 62, 125, 175 Hz and others) where there is a peak or null with a long delay time, much longer than other frequencies. Hand calculation of the expected room modes fits this observation. At 40 Hz, the sound wavelength is about 28'. Half wave is 14', which is nearly exactly the length I'm listening across. So room modes are important for an average sized room. The 40Hz peak is +10dB (above mean). the others have similar decay times but are not as strong, although the dip at 63Hz is nearly -10dB.
I moved my listening position (sofa) out  into the room away from the wall. I placed it 1/3 of the length of the room (recommended). New measurements are now quite different. All modes are suppressed to different degrees, but are still there. The software cannot find any modes, although I do have irregularities in freq response.
Listening position is a major factor in suppressing room modes. The explanation is that the new listening position is near a null in the 40Hz room mode. The conclusion is that room modes are important for bass. If you want good sounding bass from 30Hz upward, room modes must be considered.
Now, imagine I were to use the DARO system in my previous listening location. The DARO would call for 10dB suppression at 40Hz, but also for a approx +10dB increase in SPL at 63 Hz. This means that DARO would be calling for 100x more power from the sub amp (see https://geoffthegreygeek.com/amplifier-power/). This is very difficult to do for most amps. The DARO can reduce peaks, but cannot be used effectively to remove dips.

In order to effectively suppress modes, several things are needed prior to using DSP.
.First, get the sub away from the walls and corners. Get it (them) out into the room (unless you want your bass to overpower everything else).

Second, use the recommended listening position.
Third, after the first two are done and characterized, add room treatments that includes corner traps and bass traps for the low frequencies. These absorb the appropriate frequency bands so the standing waves are absorbed, not reflected. Additionally, the long reverberation will be dramatically reduced.
The first two modifications will get you a long way, but room treatment is absolutely needed to suppress the remaining modes, unless you are fortunate or the modes are sufficiently suppressed for your taste.

After the above three things are done, then the DSP (such as DARO) can be used as the peaks and nulls will be of lower amplitude and therefore the amp will not be stressed as severely.
In conclusion, room modes determine the lower frequency response of an audio system. The exact modes depend on the room size and geometry. Room modes cannot be corrected entirely with DSP software, especially nulls (dips). 
The modes are there whether DSP is used or not. Optimal location of the sub(s) and the listening position is vitally important. To avoid excessive use of amplifier power, add room treatments prior to adding DSP.
Please note that there are other considerations if two or more subs are used as they can be placed such that certain room modes can be suppressed. But room modes are still present since these are characteristics of the room only . One person's solution may not work for someone else. Other modes may not be.suppressed. Room modes are always present in a room since these are characteristics of the room only . It doesn't matter what is in the room, the modes still exist. Any item added to the room can only affect the relative amplitudes of the room modes (this goes for treatments also). One person's solution may not work well for someone else.

Even without a room analyzer, one can improve the performance of an audio system. Searches will provide guidelines, such as placing the listening position about 1/3 (actually 0.38) of the distance between the walls behind the speakers and the listener..

Some boilerplate - I am not affiliated with any manufacturer of audio equipment, room treatments or DSP. I have no interest in selling you anything.  I have an MS in Physics and over two decades designing and building optical systems (telescopes for example). Wave phenomena are very familiar to me.
Constructive criticism is always welcomed.