how movies really sound
Although many presume that Ken Kreisel products are purely home theatre products, their origins and continued development are very much based on high fidelity music reproduction. His first subwoofers were designed to extend the bass response of panel loudspeakers such as Quad electrostatics back in the early 70s. Ken was then commissioned by Steely Dan to design a full range loudspeaker/subwoofer system for the mastering their 1974 album, Pretzel Logic.
A long line of industry firsts and technological innovations followed (more here), with much of the technology adopted by the movie industry over the years, leading to home theatre as we know it today, including the now commonly known "active subwoofer".
When using a subwoofer, large, full range loudspeakers are not needed, meaning the loudspeakers can be smaller in size, taking up less room. Smaller cabinets are far less resonant, resulting in less coloration and greater accuracy. As the loudspeakers no longer need to produce deep bass, the load on the amplifier is greatly reduced too, allowing it to play louder and remain more stable during busier scenes.
low crossover point
One benefit of using multiple HF drivers is being able to use a low crossover point between high and low frequency drivers. A typical hi-fi loudspeaker is usually based somewhere between 2kHz and 5kHz, which sits within our ear's most sensitive part of the frequency range - Ken Kreisel designs use 1.6kHz to avoid this, and also creates a more 'point source' sound reproduction, causing less off-axis issues, and creating better imaging and effects placement.
This also allows the listener to sit closer to the speakers without hearing individual drivers.
Using multiple drivers boosts output when placed in a line-array (one above another). Each additional driver adds an extra 3dB to the overall output of the loudspeaker, doubling it's output for each driver added. This allows a small loudspeaker to be able to output much higher volumes than conventional loudspeakers effortlessly. Smaller drivers react faster, producing greater accuracy. A phase-focused crossover keeps the loudspeaker acting more like a point-source loudspeaker and avoiding phase issues.
All Ken Kreisel loudspeakers use sealed cabinets. Unlike ported hifi loudspeakers, this allows them freedom of placement within any room, and can be wall mounted without detriment to the sound. Sealed cabinets will produce a more consistent end result in any number of different rooms. Sealed cabinets possess a better transient response than ported speakers, producing faster and greater dynamics. They also produce better timing, and a more accurate reproduction of the source signal, and more able to convey micro-dynamics.
It is important for the front left/centre/right speakers - those that produce the majority of what you hear during a movie - to produce a consistent front soundstage. Conventional speaker systems don't do this correctly, essentially using a derivation of the front left/right speakers lying on its side, producing different dispersion characteristics. Ken Kreisel speaker systems use the same loudspeaker across the front to produce a correct, and more natural and cohesive soundstage.
3D tripole effects loudspeakers
Loudspeakers are generally designed as a monopole - they fire in one direction, forward. This is fine when two speakers can work together to produce a soundfield, but a lone effects speaker on a side wall is easily located. By adding side firing drivers to the cabinet working in opposite polarity, sound from a single loudspeaker is spread up and down the room, creating a more diffuse effect that is unable to be located to a specific point.
This diffuse sound more closely mimics the multiple loudspeakers that line the walls of cinemas.
phase focused crossovers
A single driver is the most ideal approach in order for all frequencies to emanate from a single point for a more natural and accurate listening experience. Ultimately though, a single driver is frequency limited.
Ken Kreisel's phase-focused crossovers ensures that even the sound from the 8 driver K700 is fully coherent, interpreted by the ear as a near point-source, and reach the listener at the same time.
Like loudspeakers, subwoofers greatly benefit from sealed cabinets. Ported cabinets produce phase issues, sometimes port noise, aren't always very easy to place for the best performance, and require extensive room correction. Sealed subwoofers remove these issues, and produce far better transient response and speed, resulting in a more accurate reproduction of the source signal. Contrary to popular belief, ported subs don't reach deeper than sealed. A sealed subwoofer produces a gradual and more natural bass roll-off, whereas a ported subwoofer's bass response might be better around the tuned port frequency, but drops off quite quickly beneath it.
12" drivers seem to be the ideal size to balance air shifting abilities against speed. Larger drivers are much heavier and cannot respond as quick as a smaller, more lightweight driver, needing help from servo systems and huge magnets to perform adequately. Larger magnets need stronger gaskets and support, and you're then solving issues that can be avoided in the first place - there is far more to quality subwoofer reproduction than being able to shift a lot of air.
Going to great lengths to produce the most accurate subwoofer possible takes time and development. So if you want to produce something better, do you redesign from scratch? Why, when you've already produced the best subwoofer possible for the money? Making a larger version will only compromise the accuracy and quality of what's already been achieved, ending up as an inferior flagship model.
Each stacked subwoofer doubles the output and increases depth, taking up no more floor space than a single subwoofer. The placement of the push-pull drivers (underneath and on the side) allows a stacked subwoofer to be inverted, which then places drivers on the opposing side of the cabinet to the first subwoofer, adding the benefits of force cancelling. So by adding a second, you've increased headroom and dynamic capability, decreased distortion levels, helped ease room issues, and deepened bass to boot. And all this with the same speed and accuracy of the single subwoofer.