Big Kat Revelator
Near Wall Specific™ Full Range Tower Loudspeaker
An entire new level in Near Wall Specific Loudspeaker Performance

Big_Kat_Sapele_Right_Lee_TaylorAt right is the Big Kat Revelator Signature, a slender tower loudspeaker built with our custom Scan-Speak woofers and available with a selection of tweeters. This loudspeaker was designed specifically for near wall placement and to be fully compatible with both valve and transistor amplification. The woofer loading is fully tunable QB3 vented, so one can configure the bass response to optimally mate with the room and amplifier - bass anywhere from light and tight to aggressive and snappy. The midrange is rich and clean, the lower treble perfectly balanced without a touch of forwardness, and the top end has that beautiful softness characteristic of the best silk domes.

The cabinet width is kept to an absolute minimum, and along with crossover component and driver matching, the Big Kat is capable of an extraordinary three-dimensional presentation. Microdynamics are exceptional, and the fine imaging and sound stage cues lost with most loudspeakers are clearly captured and expressed.

The Big Kats are also incredibly easy to drive. High power tube amps eat them up, and SET's love 'em.

The photo at right is the Big Kat Revelator Signature in
Tiger Eye Sapele, courtesy of Lee Taylor and Company. 

 

Design Concept

The Big Kat loudspeaker family was conceived as a cost-no-object, high sensitivity, high output full range loudspeaker designed for the most demanding two-channel and home theater environments where near wall placement is absolutely necessary.

The most overlooked aspect of loudspeaker design is that to perform their best, it is essential to conceptualize from the beginning not only the specific application but also the expected room size and placement constraints. The Big Kat is destined for mid-sized listening rooms (from 1500 to 3000 cubic feet), and because of its Near Wall Specific™ placement constraint, they must be placed within eight inches of the wall to perform as intended. This is an essential design constraint, as to get deep bass at high output in rooms this size, one can not rely only on the woofers but also on the proximity of the boundary to assist the rear mounted port in fully pressurizing the room. Therefore, the Big Kat’s low end corner is set around 38 Hz and voiced with just a touch of extra impact to create a fuller sense of deep bass extension.

The Big Kat design goals are:

High Sensitivity
Ultra-Flat Frequency Response
High, Stable Input Impedance
Bass Extension to below 40Hz
Subwoofer Compatible

 

Woofer Selection

The woofer we selected for the Big Kat is a custom 5" built on Scan-Speak’s 15W Revelator platform, called the North 15W-4531G00SC. This driver is built with beautifully cast and finished "grasshopper" frame, an enormous, stacked motor structure and unique, patent-protected pole with multiple Faraday rings. This configuration allows the voice coil to travel in a linear magnetic field that is constant regardless of excursion, resulting in the lowest harmonic distortion of any mid-woofer available.15WSC

The 15W cone is hard paper which is sliced at computer optimized angles to eliminate the channels that allow wave reflection within the cone body. This and a variable thickness cast rubber surround allow undistorted piston cone motion well into the lower treble and far above the system crossover frequency. The drivers’ smooth roll off at the top end clearly indicates there is no energy stored in the cone, rather it is perfectly absorbed by the surround.

Lastly, no compromises were made in terms of dynamic range. The dynamic range of a loudspeaker is usually limited by driver excursion. Most mid-woofers have very limited excursion - usually only 6mm, hence at even moderate volume levels they become non-linear and begin to distort. The 15W’s have linear excursion of 13mm and maximum excursion of 19mm peak-to-peak (nearly three quarters of an inch!). This is more than three times the excursion capability of conventional 5" woofers.

Scan Speak 15W woofer, optional shielding

 

Tweeter Selection

For our Signature performance level, the Scan-Speak D2905/9900 Revelator is the tweeter of choice. It features a 28mm hand coated silk dome, aperiodic rear chamber, overhung voice coil with a Faraday cap at the top of the pole, a rugged " thick machined aluminum face plate with an optimum contour to control vertical dispersion, and a unique machined top plate that channels reflections from beneath the surround away from the dome. The Scan-Speak D2905/9900 Revelator is considered by many to be the best sounding soft dome ever made.

 

System DesignD2905-9900_Small

As stated above, the Big Kat is designed for near wall placement in mid-sized listening rooms. This is intended to be compatible with most flat screen televisions, audio equipment racks, and significant others.

As it is anticipated that many Big Kats will find their way into home theaters, much of design effort was put toward AV applications. The most critical aspects of high end home theater are 1) exceptional accuracy throughout the spoken human vocal range, and 2) unrestricted dynamic range. "Voicing" a loudspeaker to reproduce spoken voice is very difficult, not only because the fundamental frequencies are actually in the upper bass, but also because the ear is far more sensitive to inaccuracies in voice reproduction than it is to music reproduction. So here the entire loudspeaker had to be optimized for spoken voice beginning with the deep male voice, and working on up in frequency.

The single most important attribute of a great loudspeaker for 2-channel applications is that it must be a joy to listen to for extended periods regardless of the type and scale of the music being played or its volume level. Voicing the loudspeaker entirely by ear while making extensive measurements to confirm free-field frequency response remains ruler flat leads to a midrange that is rich and detailed, and will not get forward or hard even at extremely high volume levels, and that the harmonic balance is correct throughout the entire loudspeaker’s bandwidth. This was accomplished by employing our unique progressive-slope crossover, which precisely mates the drivers’ natural frequency responses and the effects of the acoustic field.

The measurements of the Big Kat - Rev/Rev are shown below:

Big_Kat_Freq_Spread
BIG KAT FREQUENCY RESPONSE SPREAD

Note that the scale is 5dB per major division, twice the resolution of most published graphs. By concentrating on the most critical region of the frequency spectrum - the midrange - and other than the classic BBC Dip at 3200 Hz, our target anechoic frequency response measured better than 1.5dB from 350 Hz (just above middle "C") to 18 kHz (the mid-treble), a bandwidth of over 5 octaves. We also required nearly flat power response, perfect constructive interference through the crossover transition region, and no peaks in the off axis response.

The Big Kat's measured-and-spliced frequency response is 1.5dB from 40 Hz to beyond 20kHz and actually 0.5dB from 80 Hz to 2.5kHz, simply spectacular for a small full range loudspeaker.

The antiphase null is greater than -20dB, and beautifully symmetric, indicating there are no frequency response peaks off axis (regardless of the axis selected). This stabilizes the sound stage and improves image focus even in rooms with difficult reverberation fields.

Bass response -3dB point is 38 Hz. One can easily and precisely tune the low end in both quantity and quality to perfectly match the amplifier and room placement. For cabinet drawings and fine tuning instructions, click here.

 

Waterfall Plot

This waterfall plot is taken at 1 meter, 2.5 degrees on the horizontal axis. Note that the scale is 30dB, offering twice the resolution of typical waterfall plots. We can do this because the decay is so fast and so clean there is very little decay information above the -30dB threshold.

Big_Kat_Waterfall
BIG KAT WATERFALL PLOT

The entire tweeter decay takes place in less than 1msec, indicting the tweeter dome is well damped, there are no reflecitons off the baffle, and the high pass crossover is very low Q. This is one benefit of using the concave Revelator face plate to control horizontal dispersion, whilst the large round-over of the baffle edge minimizes the usual 2kHz baffle "bump".

Note that the decay is an almost perfectly straight angle across the noise floor. What this means is that the phase is carried smoothly from the woofer to the tweeter (a second benefit of the 1/2" thick machined Revelator face plate and our crossover topology), that the mid-woofer's cone resonances are well controlled, and there are no reflections off the front baffle.

The photo at right are the Big Kat Rev/Rev Signature crossover networks. The woofer network is on top, the tweeter on the bottom right. The tweeter in the photo is the Scan Speak D2905/9900 Revelator, along with its frequency response curve. All North Creek drivers are serial numbered, tested and had matched.

Big_Kat_Crossovers

Big Kat Crossover Network

Note that the 10 Gauge woofer inductor in larger than the 5" diameter Revelator faceplate, larger than the woofer cone! Also note all network connections are hard-wired, point-to-point, and all connections are crimped, then soldered with Kester silver solder. All terminals are gold-plated.

Even though the network is built with as few elements as possible and is a relatively simple topology, a pair of Big Kat Rev/Rev Signature crossovers weigh in at a very hefty 32 pounds.

 

 Input Impedance

This measurement was also taken with the equivalent of a 2.83V input, so the low frequency characteristics are properly documented.

Big_Kat_Impedance
BIG KAT INPUT IMPEDANCE

Above is the Big Kat Revelator system input impedance. The port tuning is 35 Hz. The 23 Ohm impedance peak at the crossover frequency is evidence of the low-Q nature of our crossover network. This peak usually does not affect transistor amplifier performance. With tube amplification, the interaction of the impedance peak and the amplifier output transformer impedance results in a slight "filling" of the frequency response through the transition region, and a richer upper midrange character. For amplifiers that are uncomfortable driving the higher midrange impedance, an additional impedance compensation "twister" circuit can be employed that adjusts the system to a nearly flat 7.5 Ohm load from 150 Hz to 20kHz. Other than the split peaks surrounding the port tuning, with the addition of the optional impedance "twister" circuit, the impedance measures an ultra-stable 7.50 Ohm 2.50 Ohm. With the "twister" installed, even the most modest tube amplifier can drive the Big Kats with ease.

Valve Amplification

Unlike transistor amplifiers, which by virtue of their extremely low output impedance are relatively non-pulsed by frequency-dependent impedance variation, all traditional tube amplifiers are coupled to the loudspeaker via their output transformer. The most significant advantage of driving a loudspeaker through a transformer is that via impedance matching it allows the maximum power to be delivered to the loudspeaker with a minimum of stress on the output device (the tube). The disadvantage is that a loudspeaker is a frequency dependent – and frequency reactive – device. Loudspeakers designed for transistor amplification are rarely tested for their compatibility with tube amplification, and in many cases frequency dependent input impedance makes them a poor match.

Considerable emphasis was placed on impedance stability throughout the Big Kats' design process, resulting in an ultra-stable 7.50 Ohm 2.5 Ohms throughout most of its operating bandwidth. The Big Kats are a perfect match for most valve amplifiers.

 
Kitty_C_Sapele_Lee-Taylor
Big Kat Center Channel, in Lee Taylor Sapele


Center Channel and Surrounds

At right is the Big Kat Center Channel (which is also called the Kitty Kat Center Channel, the Kitties are the Big Kats' little sisters). Voicing of the Big Kats and Kitty Kats are identical, so one may use the Big Kats for the main front speakers and the Kitties for the surrounds.

 

Subwoofers

Even in the low end, where an f3 of 38 Hz would seem a little lean and many amplifiers run out of steam, the Kats have a unique fullness and the ability to naturally resolve the smallest details with ease. None the less, among the original intents of this loudspeaker was to make it easily mated to a sub, so that one can run stereo mains or the entire home-theater satellite system with modestly powered transistor or tube/SET amplification, and drive the subs with their own dedicated amplification. For stereo applications, the best way to do this is to add a single 0.1uF Crescendo capacitor between the pre-amp output and the inputs of the amplifier driving the mains, blocking the low end below 80 Hz, and sealing the Big Kat's ports. Setting the subwoofers' low pass to about 65Hz with a third or forth order low pass filter, integration is seamless, adding a solid foundation to the system without compromising its performance higher in frequency.

 

Subjective Performance

The most amazing quality of the Big Kat family is their ability to resolve seemingly endless layers of nuance and subtlety that only the finest loudspeakers can capture. These are not bold, aggressive loudspeakers; rather, they have a delicate touch and excel at microdynamics, harmonic balance, and a natural sense of timing and fluidity. Even when driven by as little as three Watts, the Big Kats do not sound like they are reproducing music; rather, they seem to embrace it.

Big_Kat_Zebra_Lee_TaylorA long time reference is Bonnie Raitt ballad "Louise" (Warner Bros. 9-26242-2), a complex mix with two lead guitars and vocals floating top dead center. One can clearly discern the individual instruments' character and the musicians' fret styles, and Ms. Raitt never sounded better.

Putting on Putamayo "Women of Spirit" (PUTU1137-2) Sibongile Khumalo, "Untold Story", the scale of the entire piece is perfectly represented while ambient acoustics float through the entire room. Ani DiFranco "Cradle And All" (Putomayo "Women's Work" PUTU128-2), a very well mixed live recording, her message is frankly conveyed and the power in her voice enthralling.

From 70 Hz on up, driven by a good transistor amplifier, the Big Kat Signature is simply the sweetest, most liquid, most musical loudspeaker this company has ever produced. Not only does it perfectly capture both the male and female voice with unbelievable realism, but it also reproduces every instrument with a subtlety of microdynamics and wealth of detail that is just wonderful to listen to and sometimes flat out amazing.

One of our reference CD's is "Women of Spirit" (Putumayo PUTU137-2/M1337-2, www.putumayo.com. This is just a spectacular collection of women vocalists from around the world. Track 5 features Susan Baca (Peru) accompanied by guitar and hand drums. The recording is exceptional, and challenges the Big Kats as Ms. Baca's harmonic range is centered on the crossover frequency. Any fault in the transition from mid-woofers to tweeter would be clearly audible. The Big Kat's crossover is so seamless that Ms. Baca's voice is reproduced with exceptional naturalness and perfect harmonic balance. This is the ultimate test of a loudspeaker.

Big Kat in Zebrawood, courtesy Lee Taylor and Co.

The Fairfield Four "Standing in the Safety Zone" (Warner Bros. 9 26945-2) is a great collection of male vocals. Our reference track is "Roll Jordan Roll". This is a difficult test for a loudspeaker as all of the vocal fundamentals and most of the harmonics are reproduced by the mid-woofers, but the majority of the tenors' harmonics are in the transition region and reproduced by both the mid-woofers and the tweeter. Here again the crossover is so perfectly executed that there is no hint of the transition, the vocals absolutely convincing, and the scale of the piece is captured perfectly, with the performers behind and well outside of the speaker positions, one even beyond the side walls.

Digging out the classics, the Yes-Years remastered classic "Heart of the Sunrise" form "Fragile" (Atlantic 19132-2, 91644-2 remastered) is remarkably well preserved for 1972. Here the layers and layers of the overdub-happy 70's are beautifully captured and the texture of Chris Squire's masterwork is crisply reproduced.

Another reference track is from Genesis "Selling England by the Pound" (Atlantic 19277-2, a 1983 CD of the 1973 recording), the song "Cinema Show". This is a very good recording from that era, and the performance has layers and layers of detail. There is a point where Phil Collins and Peter Gabriel are harmonizing, their voices are so similar that for years I had thought this was Peter Gabriel's voice overdubbed. Through the Big Kat Signatures, one can distinctly hear which is Phil Collins and which is Peter Gabriel, with their very slight differences in accent clearly discernable.

The Grateful Dead "Workingman's Dead (1970 Warner Bros 1869-2) "Uncle John's Band" the harmonizing is just great, each voice separate and all together. "Cumberland Blues" is also a lot of fun to listen to.

Little Feat "Roll Um Easy" ("Dixie Chicken" Warner Bros W2-2686), simple but the layer's of complexity in Lowell George's voice clearly communicated.

 

Big Kat Rev/Rev SignatureBig_Kat_Gray_Lee_Taylor

Drivers are Perfect Pair, magnetically shielded Scan Speak D2905/9900 Revelator tweeters and Perfect Quad Scan Speak 15W/4531GK00SC shielded mid-woofers. The drivers are broken in for 48 hours, numbered, thoroughly tested and hand matched to 0.5dB, and are provided with frequency response and impedance curves.

The crossover network is fully assembled (hard wired) from our finest, hand-matched components. All inductors are 10 AWG North Creek Music Coil inductors; all resistors are NORTH non-inductive wire wound. The tweeter network features fully cascade-bypassed Crescendo capacitors. The woofer section uses Zen capacitors cascade-bypassed with Crescendo capacitors. All told, the crossover network weighs in at about 30 pounds.

Internal wiring is 14 AWG OFHC copper to each woofer and 14 AWG Tef-Flex AG silver-clad OFHC copper to the tweeter. Binding posts are North Creek Big Posts. All connections are gold plated. Big Toes and Very Big Toes with inserts and lock nuts, mounting screws, gaskets, etc. are also included, and no soldering is required. In short, everything except the wood

Big Kat Rev/Rev Signature ...$2,899 per pair  Retired 2015

North Big Kat Revelator at right, in gray scale.
Photo courtesy of Lee Taylor and Company,

Click  for cabinet plans.

 

Suggested Systems:

We designed the Kat family of loudspeakers with the home theater in mind. The recommended system includes the Big Kat Revelator system as the left and right mains, the Kat Center Channel, and the Kitty Kat Revelator Bookshelf Specific™ monitors for surrounds. There is special pricing available on the Kat package, please see the

 

Designer's CommentsBig_Kats_Lee_Taylor

Different versions of this loudspeaker were in and out of the listening room for almost five years, and in fact the original version (which was not intended for tube amplification) eventually went the path of a fully shielded system for AV systems, and which definitely had to be used with a subwoofer. A dedicated channel was also designed, and this became our home-theater-specific "Vision Revelator" loudspeaker system. Evolving from the Vision was our unique MAPD bass-loading technique, which was not only incorporated in the Vision but also the two North Tweeters, the 25mm North D25-06S and the original 28mm North D28-06S.

None the less, I remained determined to make a tube-specific system and in particular a high efficiency system for SET's and OTL's. I had several e-conversations with Bruce Rozenblit of regarding the optimum performance goals of a loudspeaker that was designed specifically for his OTL and SET-OTL amplifiers, and this eventually led to the Catamount family of loudspeakers, visually identical to the Visions and Big Kats, but requiring three to four feet of floor space behind the loudspeaker to work their best.

After we discontinued many of our loudspeaker kits in late 2006, we continued to strong sales of our Echo, Okara-II and Kitty Kat Revelator loudspeaker kits and systems, all of which are Near Wall Specific™ designs. The spectacular success of the Kitty Kats in particular lead us to look into developing and MTM version better suited for larger listening rooms.

So in December the Big Kat prototypes made their way into the North Creek listening lab, and in May 2008 had come to achieve the same level of performance that the Visions, Catamounts and Rhythms. This in a Near-Wall-Specific™ loudspeaker is quite remarkable; frankly, until I did it, I did not think it was possible.


The photo at right is a Big Kat Revelator Signature with grille by
Lee Taylor and company. Contact Lee directly though his web site,

 

This publication is copyright © 2014 by North Creek Music Systems, Inc. All right reserved.

Near Wall Specific™ and Bookshelf Specific™ trademarks are the property of George E. Short III and used with permission.