KENWOOD KFC-XW1300DVC

To say the KFC-XW1300DVC looks like a spectacular piece of work is putting it mildly. Kenwood has obviously invested a substantial amount of engineering time and money to develop a product like this. The overall motor configuration of the KFC-XW1300DVC is not your conventional single voice coil single gap, but has a dual voice coil and dual gap layout, something Kenwood calls a "multi-bias magnetic circuit." Since this is a DVC (Dual Voice Coil) woofer, each terminal is connected to one of the upper and one of the lower voice coils. While this is not a patented magnetic circuit, there have been a number of dual gap dual coil patents over the years similar to this, some coming from pro sound companies. Kenwood engineers claim that the dual gap configuration will have more linear forward and backward movement which in return should reduce distortion compared to a conventional design. Beyond this, the other important advantage is probably the enhanced heat dissipation that is split between two coils. In terms of excursion, operation is similar to a standard single gap, single coil motor.

While on the subject of the KFC-XW1300DVC's motor system, readers will be interested to know that Dr. Wolfgang Klippel has graciously loaned a Klippel analyzer for use in CA&E reviews. This amazing machine allows engineers (quite a number of car woofer manufacturers now use the Klippel analyzer) to get a better look at large signal (high SPL) performance in a woofer. Pat Turmire, CA&E reviewer and CEO of Red Rock Acoustics, performed the Klippel analysis on the Kenwood KFC-XW1300DVC woofer, including the Bl curves. The Bl curve shows the motor strength of the woofer as it moves in both directions from center. The other recorded curve is a sort of displacement curve. Ideally, the Bl curve would be centered on the 0mm point (where the cone is positioned when there is no signal). When a woofer shows an offset, it means that the mechanical system has not been completely optimized and it will run out of out the gap faster in one direction than the other, and this means more distortion at high operating levels than if it were operating perfectly symmetrically. This type of offset is pretty common. While it doesn't mean the woofer is not working sufficiently well to be seriously impressive, it does mean that it could be further optimized and enhanced. As you can see, there is an offset in the KFC-XW1300DVC and its Bl is biased about 2mm to the rear, according to the Klippel machine. Not a fatal flaw, but this does indicate that you could probably exact some additional performance out of this already high performance woofer.

At first glance the KFC-XW1300DVC is visually impressive. The woofer is built on a proprietary two-piece die-cast frame with the front half containing the cone assembly and front mounted spider, and the back half the motor assembly, rear mounted spider plus pole piece and pole vent. The frame has 12 spokes; six to support the mounting flange and six to support the front spider mounting shelf. This is fully vented for cooling. Additional cooling comes from the vents and fins on the bottom half of the frame. Since there is no backplate, air flows on both the front and back of the voice coil in both directions -- very cool, literally! The mounting lip has a thick front rubber gasket with metal Kenwood logo inlays and mounts with eight screws or bolts to your enclosure.

The motor assembly for the KFC-XW1300DVC is also unique. Rather than the conventional frontplate and backplate arrangement, the KFC-XW1300DVC motor instead has two frontplates, perhaps better described as front and rear gap plates. Since there is no backplate for a pole piece to be attached to, the pole piece is attached to the back half of the frame assembly that also has the venturi-type exhaust for the pole vent. The pole vent is 1.25 inches in diameter through the pole and expands to a 2.5-inch exhaust port at the back of the rear half of the two-piece frame. Since there is no backplate, the pole is extended 13mm in both directions. And, like most of the larger companies in the business, Kenwood engineers used computer FEA (Finite Element Analysis) software to optimize the motor parts.

Like the motor system, the cone assembly of the KFC-XW1300DVC is proprietary. The cone, a 13" rather than 12", is actually a two-piece type with a non-pressed pulp-type rear cone combined with a PBO cone pressed into what Kenwood calls the "Tornado" shape. PBO, also known as Phenylene Benxobisoxazole (yeah, I can't pronounce it either), looks like aluminum but is a woven fiber that has a tensile strength greater than Kevlar and carbon-fiber. It's extremely stiff and provides a rigid piston -- the goal for every subwoofer. The PBO cone is also a single piece cone so there is no dustcap. Coupling the cone to the motor is an 80mm-diameter (3.14-inch) voice coil wound on an FPR (Fiber Resin Plastic) high temp former that has two separate, two-layer voice coils. Each layer is wound with flat wire, like the edge-wound voice coil mostly used in high SPL pro sound woofers.

Suspension for the KFC-XW1300DVC is provided by a 1.25-inch-wide rubber NBR (a compound of rubber and plastics) surround and two oppositely positioned 8.5-inch-diameter linear conex spiders, one mounted above the voice coils and one mounted behind the voice coils. Lead wires from each voice coil pair were woven into the top spider to prevent noise and connected to a pair of color-coded, gold-plated, five-way binding posts. Just below each binding post set are sockets with 25-amp car fuses. If you blow these, either your car just got caught beneath a falling high voltage power line, or your girlfriend just twisted the volume control up to 10 with her knee while reaching for her purse.

In the Lab
Parameters for the Kenwood KFC-XW1300DVC were measured using the LinearX LMS (with the Windows LMS4 software) analyzer, the new Windows version of LEAP (LEAP 5.0 Enclosure Shop software) and the LinearX VIBox. Tests were comprised of both free-air and added mass (delta mass) impedance sweeps done using the current source (admittance) method. This means the woofer was connected directly to an amplifier (not through a 600-1000-ohm resistor) and the voltage and current measured separately at a series of successively higher voltage levels, with each two-curve pair (voltage and current) divided to produce an impedance curve. Measurements were taken a 0.3V, 1V, 1V with added mass, 3V, 3V with added mass, 5V and 10V. I was not able to use higher voltage sweeps on the XV1300 as in free-air it begins to exhibit non-linear behavior that data cannot be derived from. This data was copy/pasted into the LEAP 5 software and the curve fitting parameter derivation menu used to produce the T/S parameters and computer box simulation data provided in the Data Chart.

T/S parameters depicted in the Data Chart were used to perform computer box simulations. The KFC-XW1300DVC was designed for high SPL performance in small sealed boxes, so I set up LEAP 5 to simulate the woofers operation in a 0.55ft3 and a 1.0ft3 sealed enclosure, each with 50 percent fill material (fiberglass -- note that while fiberglass isn't necessary to damp high frequencies in the box, it does minimize the box Qtc for a given box volume).

In the 0.55 cubic foot closed box, the KFC-XW1300DVC produced a low-frequency rolloff of 55.2Hz with a box Qtc of 0.83. The graph curves in Figure 3 show the SPL at 2.83V (blue curves) in half-space, at 2.83V in a small 154-cubic-foot car compartment (black curves), and at the SPL at a power level required to get maximum linear excursion (red curves). The 0.55-cubic-foot sealed box curves are solid lines and the 1-cubic-foot box curves are the dashed curves. Increasing the voltage input to the computer simulation to 56V pushed the woofer excursion to Xmax +15 percent and yielded a respectable 117dB.

The larger 1ft3 box simulation had a lower 3dB down frequency of 47.0Hz with a lower box Qtc of 0.69. However, as is always the case, the larger the box the further the driver has to move, so it takes less voltage to achieve the Xmax +15 percent linear excursion maximum. The computer simulation required only 44V to reach a max linear SPL of 115dB, still loud enough to leave you deaf at age 60 if you rock hard for 30 years. Since these numbers are based on steady state (sine wave) analysis, the performance with program material will be at least 2-3dB greater before noticeable distortion. You should also keep in mind that low-frequency distortion is very hard for the human ear to detect. Distortion percentages as high as 15 percent generally are not really detectable except with measuring equipment. At high frequencies where your midrange and tweeters are working, it's an entirely different story.

Kenwood has a reputation for building quality audio products and the new Excelon woofers are good examples of this. While the KFC-XW1300DVC probably won't be a big hit with the dB Drag crowd, it's got more than enough muscle to do the job for the rest of us. While the type of analysis you just read about describes the technical aspects of a woofer's performance, it really doesn't address the actual subjective sound quality. For that, we ask Eric. --V.D.

Subjective
Well Vance, the new Kenwood KFC-XW1300DVC is an oddity in a sea of new oddities that are becoming the common place in design and function. Kenwood has gone out of its way to create an odd subwoofer. Much like JL Audio, Kenwood has gone the route of odd size 13" sub, not the standard 12" or a 15". The KFC-XW1300DVC is also a very tall subwoofer with a height of 10 3/5 inches, giving an almost square appearance to it out of the enclosure. It even has a different looking cone that is made of a woven PBO fiber and features an embossed tornado shape.

Kenwood has invested a ton of money in the tooling to produce this subwoofer and the technology to design it. It's a big subwoofer, a real hulk. As I have written about in past articles, it seems that the new rave in subwoofer design is big in all phases of design.

Installation
I got a hold of Rick Noetzli, Kenwood's Director of Training, to get some insight into this fascinating subwoofer and to get the company's official enclosure recommendation for maximum sound quality. I asked Rick why a 13" over a conventional size. His answer was a bit anti-climatic. I was hoping for some breakthrough in geometric design or some computer modeling FEA superiority or at the very least a bunch of marketing mumbo-jumbo to mull over and have fun with, but no, Rick said it was for the more conventional and frankly more truthful reason that a 13" is bigger than a 12" and thus should be able to move more air. Logical.

Rick recommended a sealed enclosure of 1.81 ft3. This is a gross enclosure volume, and not a net volume like most other manufacturers would give you. This means that I would not have to add the KFC-XM1300DVC's hefty displacement of 0.45 into it and that the enclosure was therefore a net volume of only 1.36 ft3. (By the way, the Kenwood KFC-XW1300DVC is now the record holder for the largest displacement of any subwoofer so far.)

I had my guys at Speaker Works build an enclosure of 1.81 ft3 and installed the KFC-XW1300DVC into it. Out to my Scorched-Earth Black Ford F-350 Super-Duty-Dually-Crew-Cab-Diesel truck to finish up the installation and set-up the listening test.

In the Ford, I found that the subwoofer worked well in most locations, but it really kicked butt with the enclosure placed on the floor between the front and back seat, subwoofer facing the rear of the cab. To power the KFC-XW1300DVC subwoofer, I ended up running (more on that later) two Crossfire VR1000d amplifiers with a bridging module. Doing this will deliver over 2000 watts of power to the subwoofer. I used the internal crossovers from the amplifiers and bypassed the subsonic filters.

The front half of my reference speaker system consists of a pair of USD Audio B-62 WaveGuide separates. This system features a pair of USD Audio 622 6.5" midrange/woofers, a pair of BC-300 horn-loaded compression driver tweeters, called WaveGuides, and a pair of specially tuned passive two-way crossovers, the PX-BCs. I power these with a Zapco Competition C2K-6.0X amplifier at 150 watts per channel. The built-in high-pass crossover filter was used to block the bass to the component system. This amp is fed via Zapco's Symbilink balanced line driver SLB-U. There are no other signal processors in the signal path.

Listening
The first song that I listened to was the title track off Harry Connick Jr.'s album We Are in Love. I really enjoy this track. It's well recorded with great detail and fantastic dynamics. It opens softly with Connick's smooth crooning and then you are assaulted by sharp, staccato attacks of horns, percussion, and a fine recording of a closely mic'd stand-up string bass.

The Kenwood KFC-XW1300DVC reproduces the string plucks from the stand-up bass with authority and the note shifts are clear and linear as the notes go lower in frequency. The KFC-XW1300DVC has no trouble going very low, with no apparent stress. Low frequency is better than the Orion H2 (see page 64) and Infinity Perfect Q that I tested, but the "jolt" factor is not as good on the Kenwood.

Next I put in 10,000 Maniacs' "Peace Train." The opening eight bars have a deep 30Hz kick drum beat, one beat per bar. It really highlights subwoofer impact and hangover (if there is any). With the KFC-XW1300DVC, the kick drum impact is very firm; hangover is noticeable but acceptable. The really fantastic part is that this sub is very impressive in its low frequency output. I really get after it on this track and crank it up. The KFC-XW1300DVC keeps getting louder and louder. At high volumes hangover gets more noticeable and the notes got a bit looser. Power handling also becomes an issue. There's a little barking as I got close to 2000 watts. Pretty good performance though. I would be inclined to try a smaller enclosure and trade off a little bit of the ultra-low frequency performance to increase the KFC-XW1300DVC's power handling and tightness at high volumes.

I break out Boston Acoustics' Music for Bottom Feeders for the third, Ramsey Lewis' "People Make the World Go 'Round." This sub can really reproduce the fundamental low, low frequency stuff. Again, it's not as tight as some of the other subs I have tested lately, but its low frequency extension and presence is more like a 15" subwoofer. Impressive. Staying in an R&B kind of mood, I listened to "Evermore" off of Take 6's So Cool album. This is a great demonstration song for this subwoofer, as it comes through snappy, with an almost physical impact. Very musical and correct sounding.

To finish off my listening test I put in the Bass Mekanik's V5.0 album, track six, "Dubalicious." This track has a very strong bass line and wonderful note shifts between 60Hz and about 30Hz. Here the KFC-XW1300DVC shines like no other sub. The 30Hz notes are every bit as loud as the 60Hz notes. Low frequency linearity and extension are the stand out features of this beast. Just to verify this, I measured the Kenwood all the way down to 20Hz and it kept getting louder and louder the lower the frequency.

Conclusion
When I first started this test, I originally ran the sub with 1000 watts. I was not impressed. While the KFC-XW1300DVC sounded nice, it did not have enough output to get out of its own way. As Kenwood recommends two of their X810Ds (2 x 800 watts) to power this monster, I decided to up the ante and added a second 1000 watt amp to reach the magical 2000 watts mark. The performance was transformed into a subwoofer that I would have no trouble recommending to just about anybody that was interested in a great, all around subwoofer -- that is, if you have the budget to power it correctly. -E.H. v