Mating a subwoofer to a quality, high resolution planar system can be a daunting task. One needs to be prudent in every step taken in potential candidates. Removing any pre-conceived bias, and any mythology toward loudspeakers in general, and subwoofers specifically, is absolutely necessary if one is to pursue the technically superior approach.
The elephant in the room is the subwoofer mythology surrounding subwoofers is "speed". Fast bass, quick bass, etc. We see these terms used frequently. There's an entirely inappropriate amount of emphasis on subwoofer speed, and it's connection to quality. When considering a woofer stroking back and forth, out-putting a 40hz tone, what impacts a driver's speed? Increasing the volume, that increases speed. It has to move more air, so it's excursion is greater, yet it must maintain it's frequency. That makes it faster. I'm attempting to illustrate why driver speed, is often inappropriately linked to quality.
Another myth is driver size, somehow being tied to quality, in that smaller, faster drivers possess a speed advantage. This is absurd. Subwoofing, no matter how one looks at it, is all about moving air in a low distortion manner. When comparing a high quality 12" LF driver, to a high quality 18" driver, the 12 must work significantly harder to output a given SPL, and frequency than the 18. The larger 18 has over twice the cone area of the 12, thus it's stroke is half of what the 12 must produce at any given frequency and SPL level. The 12, working twice as hard, will encounter it's non-linearities of cone over-shoot (the cone has to move twice the speed), the voice coil will encounter the limits of linearity of the magnetic circuit, much earlier to the similarly designed 18. There's simply too much un-due emphasis on small quick drivers, when individuals consider nice tight bass.
Oftentimes enthusiasts mistakingly consider the moving mass as a key component to how quickly a subwoofer driver can accelerate, decelerate, and quickly change position. This concept, of mass being a determinate factor of a driver's capability, is one of the most deeply rooted misconceptions, because on the face it makes so much sense, ...however wrong it may be. The driver's transient response, all comes down to how much current can be delivered by the amplifier, and subsequently properly used by the driver. Actually, as Dan Wiggins so adeptly illustrated in his work, a drivers inductance, not mass, determines it's ability to quickly start and stop.
So, what does contribute to a subwoofer either mating properly to a high resolution main, or not? A technically superior approach, in a well designed product, that's properly integrated to the remainder of the system, and ideally optimized to the acoustic interaction of the room. Simple as that
Seriously, ones subjective interpretation of a subwoofer's "tightness", or speed, is linked to sighted bias. The power of our preconceived notions are enormously significant. Unsighted or blind tests have illustrated that one must go with the science, and big drivers and their associated mass has absolutely no impact on a drivers transient response.
1.) Technically superior approach
2.) Well designed/built product
3.) Properly integrated
4.) Ideally optimized acoustically
If I were mating a subwoofer to a planar based system, and absolute seamless integration between the two elements was key, I too would employ a sealed design. When contemplating proper sealed designs, you've got to entirely eliminate the cabinet as a component to the sound. There are many such methods for controlling a cabinets contribution, one such approach is the dual opposed approach. This design cancels the mechanical forces the drivers would otherwise impart to the enclosure. So when combining a nice, robustly build enclosure, with a dual opposed design approach, all potential vibrations, resonances, etc, are entirely canceled. Additionally, the added benefit is the shared work-load between the two drive elements. When comparing to a single like sized driver, the overall capability is doubled. Or at any given SPL level, the excursion of each driver is halved. Either way you look at it, it's a technically superior approach.
Obviously, there are several outstanding, single driver subs out there. The dual opposed approach does not reign supreme in every case. Although it's a technically superior way to go about things, a very good driver in an entirely inert sealed enclosure, can achieve similar results. The added displacement of the dual opposed driver aids in it's superiority. It's all about moving air, double the cones, you half the workload. Also, when the drivers only need to move a small amount, their apparent speed is increased.
There are several other aspects of the sealed alignment that place it in the technically superior category, one being the native roll-off of the sealed design is 12db octave. This matches the a room's low frequency transfer function and Room Gain (PVG) characteristics. That's an entire different topic, suffice it to say, the sealed alignment properly executed mates up ideally with the room's acoustic.
The next aspect is a thoroughly well designed and built product. One such example I've heard is Seaton's Submersive. Few commercial subwoofers have the lower octave extension characteristics that the Submersive has. Way too often design compromises must limit amplifier power by signal shaping/limiting, to prevent nasty non-linear behavior from a product in the lowest octaves of operation. In the case of the Submersive, the designer fully realizes the importance of the realistic impact that accompany extension into the single digits. I can only think of one other designer, Nathan Funk, that has a subwoofer product in production that fully takes advantage of extension into the infra sound range. It's an added level of realism, in my experience whether one places importance on it typically is determined by if they've been exposed to it.
Now, the real key to mating a superb subwoofer to a high rez planar main is proper integration, and acoustical optimization. This is where one can really affect the apparent speed of the sub. Proper blending at the crossover, proper phase integration, so one achieves a ideally coherent wavefront emanating into the listening space,...hugely important. It's not easy achieving ideal response at the crossover, but working and working to get it right is very important.
Some measure of equalization in both the frequency and time domain is absolutely necessary to achieve a nice realistic and fully impactful product. Without EQ in the time domain, bass notes linger and sustain, masking transient detail. Every single room is different, but bass traps are vital for good delineation of bass detail and transients.
Good bass, properly blended with planar mains (or any other high quality mains) shouldn't mask any of the rest of the material. It shouldn't sound like an effect, it should be entirely whole. Percussive sounds should be realistic, not like a separate and distinct thud. Transients should hit powerful, tight and hard, but musical when appropriate. The entire system, including the bass, should be high rez and transparent. How do you get transparency? Ideal blending of the mains to the sub. For much bass instrument material, the upper harmonics are more prominent and louder than the fundamental. So working toward an ideal blend between sub and mains is one primary aspect of what really impacts apparent speed.
Production units, I'd examine the Seaton Submersive, Nathan Funk's LMS5400 based designs. Proper blending between sub and mains is discussed daily in threads all over the web,...why? It essential to a realistic experience.
Sorry for the verbose contribution, too much coffee
Good luck, and whichever route you choose, exert the effort to optimize what you buy. The vast majority of systems sit in homes under utilized due to poor optimization.
I'd strongly suggest REW, or OmniMic. I've had OMniMic for a year now, and it's severd me well,...and it couldn't be easier. Literally minutes from opening it up, you're measuring. Yes, i began with the Rat Shack digital. You can check out Rives test disc, and chart your room with the Rat shack meter. That's somewhat crude when compared with what's out there. For a newbie to measurment gear, I'd suggest OmniMic.
Thanks, and again good luck
