Borealis and Rhythm

Full Range Loudspeaker Systems
Above are the North Creek Okara II, Borealis and Rhythm Revelator

Historical Page, retired 2009

North Creek Design Goalsborzebra

Each North Creek Loudspeaker Kit is conceived as a cost-no-object high performance two way loudspeaker system featuring high sensitivity, a detailed but romantic top end, smooth, natural, articulate midrange, exceptional imaging, and an aggressive, dynamic low end.

These sound like the design goals for virtually every midsized loudspeaker system; however, these goals are rarely accomplished. First of all, transparency throughout the midrange - the single most important element in high end reproduction - is difficult to achieve with a woofer larger than six or seven inches; however, bass response into the second octave at realistic listening levels requires significant air to be moved, virtually ruling out small woofers of conventional design.

Secondly, a transparent, floating sound stage with precise image focus is almost impossible to achieve with monopole loudspeaker systems of large dimensions, again ruling out larger drivers.

Thirdly, to avoid upper midrange deterioration due to cone break-up and crossover parasitics while insuring midrange naturalness and image stability, a low crossover frequency - below 2 kHz - and uncomplicated crossover topology is required. This rules out virtually all conventional tweeters due to both power handling and excursion limits.

The systems we present here achieve our design goals by fully exploiting the remarkable capabilities of the superb , custom-made SCAN-SPEAK 18W/8545SC 7" Carbon Fiber woofer combined with several silk dome tweeters made either by Scan Speak or North Creek Music.

Borealis in Zebrawood courtesy Lee Taylor and Co.


The Woofer

The SCAN-SPEAK 18W/8545SC is a woofer of remarkable design. First and foremost, the driver is designed for enormous linear excursion. This is achieved through SCAN-SPEAK's development of the patent-protected SD-1 motor structure, diagramed below right. Close inspection of the conventional motor (above) and SD-1 system (below) reveals the following:Image25

The conventional motor structure voice coil length of 12mm or less is simply too short for reasonable output at low frequencies. Conventional top plate thicknesses of 6mm yields a peak-to-peak linear excursion of only 6mm (voice coil height minus air gap height = peak-to-peak linear excursion).
The SCAN-SPEAK voice coil length is 19mm, yielding a p-p linear excursion of a full 13mm, more than twice that of conventional woofers.

The conventional motor structure suffers from high second harmonic distortion at low frequencies due to an asymmetric magnetic field about the top plate; that is, there is more flux below the top plate than above.
The SCAN-SPEAK pole is extended well beyond the top plate, creating a symmetric magnetic field which greatly reduces low frequency second harmonic distortion.

In a conventional woofer, high amplitude excursion modulates the voice coil inductance:
outward travel decreases the amount of pole surrounded by the voice coil, reducing its inductance, where as inward travel increases the amount of pole surrounded by the voice coil, increasing its inductance. This is one reason why most woofer impedance curves do not look like a simple "resistor plus inductor" at high frequencies. This displacement-dependent voice coil inductance causes intermodulation distortion between high excursion low frequencies and higher frequency information, as well as creating frequency response aberrations by perpetually misterminating the crossover network. In addition, the inductance variations create a solenoid-type force between the voice coil and pole which introduces an offset to the coil rest position, increasing second harmonic distortion.

The SCAN-SPEAK voice coil always surrounds an equal amount of pole, eliminating this source of distortion. The SCAN-SPEAK impedance curve is retraceable independent of drive level.18W8545SC1

In a conventional motor structure, current within the voice coil creates dynamic magnetic flux which modulates the motor field by partially demagnetizing and remagnetizing the section of the pole surrounded by the voice coil. This phenomenon creates both third and intermodulation distortion throughout the midrange, and is the other reason why conventional woofer impedance curves are nonlinear.
The SCAN-SPEAK motor structure is constructed with copper rings, called "Faraday rings," bonded to the pole. The Faraday rings create a sympathetic flux which exactly matches the voice coil flux, eliminating this source of distortion.

The concave cone-shaped, vented pole top eliminates reflections between the dust cap and pole while cooling the magnetic structure.

The SCAN-SPEAK 18W/8545 cone is constructed of carbon fiber loaded paper and coated with damping compound. Damped carbon fiber is an exceptional cone material because it combines low mass with incredible strength, therefore it is extremely rigid at low frequencies yet can be easily controlled by the damping compound at mid and high frequencies. The 18W/8545SC exhibits nearly theoretically perfect performance for a 7" driver - including the rising response and gentle turnover before roll off.

One can find far more detailed information about the causes and solutions of motor-induced distortions the AES publications Loudspeakers, Vol. 1 and Vol. 2 (60 E 42nd St, NY, NY 10165). Suffice to say that the engineers at SCAN-SPEAK have used every resource to develop and manufacture a motor structure which minimizes or eliminates the common second, third, and intermodulation distortions found in virtually all conventional loudspeaker drivers, resulting in a 7" woofer with exceptional low end performance even at very high volume levels while providing midrange purity rivaling many smaller drivers. The SCAN-SPEAK motor structure is unique and patent protected.D28_Side_View

The Tweeters

The North D25-06S and D28-06S silk dome tweeters were designed by George Short exclusively for North Creek Music Systems, with excellent frequency response and impedance characteristics and requiring only a simple crossover.

The SCAN-SPEAK D2905/9900 Revelator represents the latest evolution of the tweeter which has long set the standard for musicality in soft dome tweeter design.

Comparing the North D25, North D28, and Scan Speak Revelator to conventional tweeters, one finds several differences:

Conventional tweeters are constructed with a short-coil, long-gap geometry. This provides high linearity with limited excursion (typically 0.4mm), but dictates very poor performance under high excursion. Conventional tweeters, therefore, must either be crossed over at a high frequency or be used only in low power applications. The North D25 is built with an under-hung geometry, with a short coil, tall top plate and extended pole piece, which extends the linear magnetic field below and above the voice coil. Both the North D28 and SCAN-SPEAK Revelator are constructed with a long-coil, short gap geometry; that is, they are built like a woofer. The North D28 also has an extended pole piece and copper Faraday sleeve, while the Scan-Speak Revelator has a Faraday Cap. The North D28 is diagramed below.

All three tweeters have a full 1.0mm p-p, more than twice that of conventional tweeters.


Conventional tweeters have a limited air volume behind the dome and a flat top plate, which encourages reflection beneath the dome.
The North D25, D28 and Scan-Speak Revelator feature a cone-shaped, aerodynamically flared pole piece which is vented into a rear chamber, eliminating reflections while lowering the driver resonance. In the case of the North D25 and D28, the secondary chambers are aperiodically coupled to the primary chamber, creating an optimally tuned MAPD environment for the tweeter dome.

Conventional tweeters immerse the voice coil in a thick magnetic fluid to cool the voice coil and damp the tweeter's fundamental resonance. While this is effective, the thick fluid creates frictional drag on the voice coil, slowing down the dome.  Both the North D25 and D28 incorporate an extremely low viscosity magnetic oil surrounding the voice coil, to cool the coil while minimizing drag.BobABor3

Lastly, the North D28 and Scan Speak Revelator employ an extremely thick, machined face plate, and all three tweeters feature countersunk assembly screws and provisions for countersunk mounting screws. This provides a perfectly smooth transition from the tweeter dome to the loudspeaker cabinet front.

The Scan Speak D2905/9900 Revelator has long been used in many European and American high end designs, including several that are considered by audiophiles and reviewers alike as among the best in the world. The North D25 and D28 are very similar in character, offering remarkable performance at reasonable prices.

The Borealis System

The Borealis system is designed as a cost-no-object, stand-mounted reference two-way loudspeaker system. Constructed of finest drivers and most musical crossover parts available, the Borealis combines the definitive qualities of a mini-monitor - large sound stage, precise imaging, superb detail - with the dynamic low frequency performance of a much larger system.

The Borealis system has been optimized for the ability to communicate the emotion of the musical event like few other loudspeaker systems. The light, rigid carbon fiber cone reproduces every nuance of a performance without a hint of distortion. The speed and detail in the low and mid-bass is reminiscent of smaller loudspeakers, but with a much tighter bass line. The system also excels in dynamics and dynamic contrasts, as the long linear throw of the woofer can move tremendous amounts of air. Music is reproduced with the impact of a much larger loudspeaker, but with the agility of a monitor.

The Rhythm SystemTempist1

The Rhythm loudspeaker system is a cost no object, floor standing, full range WTW (woofer-tweeter-woofer) loudspeaker system designed and constructed with the finest drivers and crossover parts available. The Rhythm combines the speed and finesse of a mini-monitor with the raw power of a much larger loudspeaker system, while flawlessly maintaining the correct harmonic balance and timbral accuracy essential to high end reproduction.

History: The MTM (midrange-tweeter-midrange) loudspeaker style was first developed by Teledyne Acoustic Research (AR) in the late 70's as a high sensitivity loudspeaker system of controlled directivity. The style soon spread to other manufacturers, of which the KEF 104 was probably the most commercially successful. At the 74th AES convention in 1983, Dr. Joseph D'Appolito presented the landmark paper "A Geometric Approach to Eliminating Lobing Error in Multiway Loudspeakers". The paper clarified the acoustic qualities of the MTM configuration, and over the next few years it rapidly grew in popularity.

Characteristics: The MTM has several desirable performance characteristics that are difficult to achieve using conventional two-way loudspeaker designs:

Sensitivity and Impedance: First and foremost, the parallel-wired MTM configuration displays a 6dB increase in sensitivity when compared with the standard two-way. The sensitivity increase occurs because the driver effective cone area is doubled while the net impedance is halved (doubling current draw). Most high quality amplifiers have little difficulty driving the lower impedance, therefore the sensitivity increase is almost without negative consequence.

Radiation Pattern: When the MTM was first used in the Acoustic Research Magic Speaker, it was done so because destructive interference interactions in its radiation pattern created nulls in the same frequency region where the "floor bounce" usually occurs. It was later shown by Dr. D'Appolito that a positive interference lobe within a 15° window centered on the tweeter axis creates a large vertical listening position with nearly identical frequency response. Both of the above conditions are virtually impossible to achieve with conventional driver configurations.

Rhythm in Sapele Veneer for NY Stereophile Show, courtesy Lee Taylor and Co.

The CabinetImage28

The 18W/8545SC is constructed with an enormous magnet structure and a very compliant suspension. Our average of forty samples over the last several years of production yields the Theile-Small parameters Qts=0.32, Fs=31.9Hz, Vas=31.5 liters. Small's EBP is 99.7, indicating a vented box. Over the years, we have found the QB3 alignment to offer the best compromise between bass extension and subjective bass quality. Therefore, our required cabinet volume is approximately 17.5 liters per woofer, yielding a tuning frequency of 39.6Hz and an F3 of 46.2Hz. The alternative construction, for the SBB4 alignment, requires a box volume of 18.1 liters, with a tuning frequency of 32Hz and an F3 of 54 Hz.

For vented box cabinet construction, we have found it best to target a QB3 cabinet and oversize the theoretically optimum volume by 15 to 20%. This extra volume provides the ability to fine-tune the system to correct for small aberrations created by inductor and speaker cable DCR, non-zero amplifier output impedance, and small variations in driver parameters. The loudspeaker cabinet volume can easily be decreased at a later date with the addition of fillers.

The cabinet is constructed based on the principles of the

Driver position is with the woofer centered and tweeter offset on the fascia. The drivers are flush mounted and the fascia edges are radiused to minimize diffraction.

Access into the cabinet is provided via an access panel in the cabinet rear. Cabinet ballast, the woofer crossover network, North Creek Glop and acoustic stuffing are installed through this panel, and additionally the low frequency tuning can be adjusted and optimized by accessing the port tube through this panel.

The Crossovers

Crossover design is the single most important aspect of loudspeaker system design, and also by far the most difficult. For most high performance systems, engineering time from concept to sign-off is 1% driver selection, 4% cabinet design, and 95% crossover.

All North Creek crossovers are developed based on the following principles:

• Smooth, relatively flat frequency response on axis.
• Power response and out-of-phase curves should be symmetric about the crossover frequency.
• Filter transfer functions should be monotomic.
• Constructive interference is good; destructive interference is bad.
• Dips are better than peaks.
• The higher the overall impedance, the better.
• The fewer components involved, the better.
• The simpler, the better.


The 6dB Response Step:

The "6dB Response Step", also called the "Baffle Diffraction Step," is the most significant acoustic phenomenon one must deal with in crossover design, and also the phenomenon most often overlooked by amateur designers. Simply put, at the wavelength of sound roughly equal to twice the baffle width, the loudspeaker's radiation pattern changes from full-space (equal energy in front of and behind the loudspeaker) to half-space (all the energy in front of the loudspeaker). What this means to the designer is that the driver which measured reasonably flat in an infinite baffle anechoic chamber (the way most drivers are designed and measured) will actually have 6dB less bass and mid-bass when located out into the room. Hence, a loudspeaker design based on flat half-space anechoic frequency response and not corrected for the 6 dB response step may sound fine when flush against the front wall, but will be thin when placed out into the room where the sound stage is best. For our 9½" wide baffle, the step gradually manifests throughout the octaves bordering 712.8 Hz.

Note that in the WTW configuration (such as the Rhythm system), the 6 dB bass and midrange loss created by the 4pi acoustic environment is compensated for by the increased system sensitivity. The resulting system exhibits a 4pi in-room sensitivity throughout the lower midrange equal to the original 2pi anechoic sensitivity of a woofer alone.


Other Frequency Response Considerations

Because we require a monotomically decreasing voltage plot across the woofer terminals and a simple crossover topology, a driver with flat half-space frequency response is not suitable (otherwise, the crossover would have to attenuate throughout the 6 dB response step region, go flat through the region above the step, and then begin attenuating again to mate the woofer with the tweeter - see Dickason Loudspeaker Recipes Figure 4.44 for example.) The engineers at SCAN-SPEAK are well aware of this, and design their woofers with a rising frequency response above 1kHz and a smooth high frequency roll off. The combination of the 6dB response step and rising driver frequency response above the step creates a monotomically rising in-room woofer response, which can be easily corrected to flat response by a simple, monotomically falling low pass electrical crossover slope.


Crossover Topology Image30

Both anechoic and 4-pi frequency response and impedance measurements were made using our Liberty Audiosuite measurement system (in MLS mode) and calibrated microphone. All measurements were taken at a high enough volume level to accurately represent the drivers' dynamic charicteristics, not their small signal behavior. The measurements were then entered into our Calsod CAD system for preliminary crossover network simulation.

Long familiarity with the SCAN-SPEAK D2905/9900 Revelator tweeter has shown that its natural low end roll off, in conjunction with a simple second-order topology high pass filter, yields an overall acoustic high pass characteristic of precisely third order. The simplicity of the lower order topologies - with only one reactive component in the signal path - will always outperform higher order topologies throughout the pass band, and the second-order topology with the trap provides both significant low frequency attenuation (imperative at high listening levels) and the ability to adjust the turnover Q. 

To match the woofer to the tweeter, a third order acoustic slope is required. Electrically, the slope must begin at 200 Hz or so at about be 2dB per octave (to correct for the 6 dB response step), gradually maturing to the higher order.

Initially, we begin with an impedance-compensated, overdamped forth order topology, including damping resistors in series with all shunt capacitors and the first inductor being about twice that expected from formulae. While this is extremely complex, it provides a suitable starting point. With five optimizable reactive components plus what amounts to three optimizable damping resistors in the woofer circuit, and six optimizable components in the tweeter circuit, a filter with the correct electrical characteristics may be quickly obtained.RhyUnlXOandDrivers3

Analysis of the sum, power, and anti-phase curves of early simulations with a 3kHz target crossover frequency, revealed that even with reasonably flat frequency response, both the power and antiphase curves were asymmetric. We then began to massage the acoustic crossover frequency while adjusting for relative driver offset, and eventually developed several physically realizable possibilities of varying complexity that were worth popping together in the listening lab.

Rhythm Unlimited Revelator crossover and drivers (at right).


Subjective Evaluation and Final Crossover Design

It is at this point of the design process that one appreciates having a dedicated listening lab, measurement equipment, a couple of fast computers, and a few thousand crossover parts - plus an automated coil winder - at their disposal. Prototypes were constructed and listening sessions began, entailing several hours per day over several months. High end crossover design is 95% listening, 5% measurements; most professional designers can come up with half a dozen combinations that all measure fine in an afternoon. A completed system must not only measure reasonably good, but also sound harmonically correct and intrinsically musical over an enormous range of material.  

Crossover design was eventually completed for both systems, and the final topology is shown below. This represents the best sounding combination, and the measurements verify that our objective goals were achieved. The tweeter section is a simple attenuated second order network with impedance compensation, while the woofer section is very low Q third order network with a damping resistor in the T leg but without impedance compensation. In both cases, the drivers' acoustic roll off is third order.

Note that the networks are completely point-to-point hard wired. The Rhythm Unlimited uses 10 AWG inductors, whilst the Rhythm Signature uses 8 AWG inductors.

The combined response is shown below, including the woofer and port close mic curves, and almost precisely matches a theoretical third order combination centered at 1.8 kHz, with the low- and high-pass frequencies staggered by a factor of 1.20, drivers in phase.


Borealis system response, one meter, 5 degrees horizontal on tweeter axis.

For both the Borealis and Rhythm systems, the frequency response is 45 Hz - 22kHz ±2dB. The zero level is at 60dB, and system sensitivities are 85.5dB and 90.5dB respectively.

Rhythm system response, one meter, 5 degrees horizontal on tweeter axis

 Note that the antiphase curve (shown above for the Rhythm system) is symmetric about the 1.8kHz crossover frequency, the antiphase null is quite deep, and there is absolutely no region of destructive interference.


 Rhythm system input impedance, normal and with impedance "Twister" correction circuit


Rhythm Crossover Network Voltage Plots

The tweeter -3dB point is 2100Hz acoustically and 2400Hz electrically, well within acceptable limits. At its 500 Hz resonance, the tweeter level is down 36dB acoustically and a full 32 dB electrically (see the voltage plot above). Also note that the tweeter filter transfer function is monotonic. Lastly, note that the tweeter response is realized with only a single reactive crossover component in the signal path. Naturally, this implies the tweeter series capacitor is the single most significant circuit element and must be of the highest quality

The woofer network topology is greatly simplified because the SCAN-SPEAK 18W/8545SC woofer exhibits perfect L+R impedance at high frequencies. Unlike conventional woofers, this impedance characteristic allowed us to consider the voice coil inductance as a series circuit element instead of forcing additional conjugate circuits to compensate for it. The topology then became simple damped third order that is correctly terminated, therefore we have precisely third order acoustic output. Also note that the woofer voltage transfer function is monotonically decreasing above 150 Hz. The other advantage to such a low crossover frequency is that the woofer is crossed out while still in piston, so any high frequency non-minimum-phase behavior and driver variation is inconsequential.

The end result is a very simple crossover network with only three reactive components in the entire signal path.  

Low Frequency Performance

Inspection of the close mic frequency response curve reveals that the port output is centered 38 Hz, very close to the vent tuning of 36 Hz. This actually represents the best sounding combination (the theoretical QB3 specification called for a 45 Hz tuning). The port is adjustable via the rear access panel, so one may taylor the tuning by as much as a half octave to best suite the associated electronics and room acoustics. The low frequency roll off is forth order below the tuning frequency, therefore the system is capable of considerable output into the high thirties. 

Subjective Evaluationborfloor1

This is of course the only important measure of a loudspeaker design's success. The criteria we evaluate are the system's overall harmonic integrity, its ability to create a convincing illusion of a live performance in the listening environment, and its listenability (a combination of the "goose bump", "foot-tapping", and "stay up late" tests). We don't consider a design completed until it excels in these three categories.

Harmonic Integrity: One would think that with modern test equipment this condition would be a given, but in reality it requires a very delicate balance between the low end tuning and midrange and top end voicing. Very small changes - on the order of 0.5 dB - over broad regions will completely upset this balance, and to further complicate the issue is the influence of the electronics and room. Our favorite test discs are Ry Cooder & V. M. Bhatt A Meeting by the River (Water Lily Acoustics 60997-0029-2) and Harry Connick, Jr. When Harry Met Sally... Soundtrack (CBS Records 7464-45319-2). The systems presented - with a very gentle rise of 1dB between 300Hz and 20 kHz on axis and a gently falling third-octave averaged room response - sound dead on.

The Illusion: In a few words: Sound stage, Focus, Presence. One must to use natural recordings of voice and acoustic music. The variations between venues is enormous, yet the system must recreate the dimensionality of each venue with equal ease. Focus and Presence are defined in lateral, horizontal, and vertical position. To this end, tight driver tolerances and 1% crossover component matching is essential. Our favorite test is track 6 of the Fairfield Four Standing in the Safety Zone (Warner Bros. 7599-26945-2), "Roll Jordan Roll". The Rhythm can focus so realistically down the middle and through the extremes that it is almost frightening. No kidding.

Image height requires an element of magic, and this loudspeaker has it spades. Our favorite studio test is the title track of P.J. Harvey's Rid of Me (Island 314-514696-2). Polly Jean's voice emanates from a precise point about four feet above and six feet behind the loudspeaker plane, literally top dead center.

Listenability: This quality has no correlational measurement. Once a system is listenable, it becomes almost impossible to subjectively evaluate because one enjoys listening to the music too much, and realizes only after the goose bumps have subsided that the goose bump test was passed. Our loudspeakers can do justice to everything from Bach to Zandig.

The floor standing Borealis (North Passion) above is courtesy of Lee Taylor and Co.

Using the 18W/8546 Kevlar woofer: BOROAK1

The 18W/8546 can be used in either the Borealis or Rhythm loudspeaker systems with only minor changes to the crossover network and cabinet.

The 8546 offers superior resolution in the upper midrange over the 8545, but is also less romantic. We generally recommend the 8546 for those using tube electronics throughout, and the 8545 for solid state and solid state/tube systems.

One can also use the standard 18W/8545 and 18W/8545-K with the Borealis or Rhythm with minor changes to the crossover.

Adding a subwoofer: 

Merging a subwoofer with the Borealis and Rhythm systems is relatively uncomplicated, although we strongly suggest an electronic crossover and separate amplifiers be employed for each system. Sealing the vent (by removing the access panel and replacing the port tube with a cover) is absolutely necessary, as is true of all vented satellites, because it forces the satellite low frequency performance to be second order high pass at the system resonance. A small series capacitor between the pre-amp and satellite power amp serves as a perfect first order high pass filter, resulting in a third order high pass characteristic overall. The subwoofer may be driven by a third order active low pass filter set at 80Hz. The subwoofer should be placed as close as possible to the room corners. We suggest dual for medium-to-large listening rooms.


North Creek Loudspeaker Kits are available packaged in component form. The package includes "soft matched" drivers (tested and hand matched to ± 1.5dB), fully assembled and tested crossovers, binding posts, grille fasteners, screws, nuts, bolts, port tubes, NCMS Soft Glue, other adhesives, and the information packet; in short, everything except the wood. The crossovers are fully assembled of ±1% hand matched components, and tested to be within ± 1% of the original designer's specifications. Color coded internal wiring is hard wired to the networks, as are the correct connectors. The first time builder can complete the project in two evenings.

Tower cabinets are available for the Borealis and Rhythm Revelator from Lee Taylor and Co.

Borealis North D25 "Aurora" Project Consists of "soft matched" 18W/8545SC woofers, Perfect Pair North D25-06S tweeters, all 14 AWG air core inductors, Zen high frequency film capacitors bypassed with Harmony capacitors, North power resistors, all crossover components hand matched to ±1%, TefFlex AG and Lex OFHC internal wiring, binding posts, etc; everything required to build the loudspeaker system except the wood. The crossover network is fully assembled and tested.

Borealis- North D25 "Aurora" Project ...$    (Retired 2009) PE_Borealis

Borealis - North D28 Project Consists of "soft matched" Scan-Speak 18W/8545SC and North D28-06S drivers, all 14 AWG air core inductors, Zen high frequency film capacitors bypassed with Harmony capacitors, North power resistors, all crossover components hand matched to ±1%, TefFlex AG and Lex OFHC internal wiring, binding posts, etc; everything required to build the loudspeaker system except the wood. The crossover network is fully assembled and tested. Component list $1024.00.
Borealis - North D28 Project ...$ Retired 2009.

Borealis D28 Unlimited Project (North Passion) Consists of "soft matched" 18W/8545SC and North D28-06S drivers, all 10 AWG air core inductors, Zen high frequency film capacitors bypassed with Harmony and Crescendo capacitors for the woofer section, all Crescendo high frequency film-and-foil capacitors in the tweeter series section, North power resistors, all crossover components hand matched to ±1%, TefFlex AGå an Lex OFHC internal wiring, binding posts, etc as above; everything required to build the loudspeaker system except the wood. The crossover network is fully assembled and tested. Component list $1,294.00.
302-734 cabinet and the MD02 cabinet are  also compatible with the Borealis.

Photo at right is the Borealis - D28 in the Parts Express cabinet.



Rhythm - North D25 Project:RHYERIC2

Consists of "soft matched" 18W/8545 and North D25-06S drivers, all 14 AWG air core inductors, Zen high frequency film capacitors bypassed with Harmony capacitors, North power resistors, all crossover components hand matched to ±1%, TefFlex AG and Lex OFHC internal wiring, Texas binding posts, Big Toe spikes, etc.; everything required to build the loudspeaker system except the wood. Bi-Wired. The crossover network is fully assembled and tested. Component list $1,109.00.
Rhythm - North D25 Project ...$ per pair  Retired
Rhythm-C - North D25 Center Channel $each

Scan-Speak D2905/9500 "classic" version is also available on a custom-order basis.


Rhythm - North D28 Unlimited Project:
Consists of "soft-matched" 18W/8545SC and perfectly matched North D28-06S drivers, all 10 AWG air core inductors, Zen high frequency film capacitors bypassed with Crescendo capacitors for the woofer section, all Crescendo high frequency film-and-foil capacitors in the tweeter series section, Zen capacitors in the tweeter parallel sections, North power resistors, all crossover components hand matched to ±1%, TefFlex AG and Lex OFHC internal wiring, Texas binding posts, Big Toe spikes, etc as above; everything required to build the loudspeaker system except the wood. Bi-wired. The crossover network is fully assembled and tested. Component list $1,648.92.
Rhythm - North D28 Unlimited Project ...$Retired.
Rhythm-C North D28 Center Channel ...$Retired.

The woofers can be ordered as broken in "perfect quads" for an additional $70 per set.

Rhythm/Revelator Project:

Identical to the Unlimited project above but optimized for and supplied with the SCAN-SPEAK D2905/9900 Revelator tweeter. Slightly faster than the Unlimited and offers even greater resolution. The crossover network is fully assembled and tested. Component list price $2,062.85.
See the review in Speaker Builder October 1999 (issue #6-99).

For our comments on the SB review,
Rhythm/Revelator Project ...$Retired per pair.
Rhythm/Revelator Center Channel ...$Retired each

The drivers can be ordered as "perfect" (broken in and matched to ± 0.25dB) for an additional $100 per set. The '8545's are a "perfect quad".LeeRhy1


Rhythm/Revelator Signature Project:
Tempest loudspeaker system)

Absolutely the best of the best. The Rhythm Revelator Signature Project, which is the North Tempest in finished form, features 8-gauge inductors, fully cascade-bypassed Crescendo and NOS Military capacitors in both the woofer and tweeter sections, crossover components hand selected and matched to ±0.25%, drivers broken in "perfect pairs" (hand matched to ±0.25dB), fully shielded 18W8545SC woofers, supplied for bi-wiring. The crossover network is fully assembled and tested. This is simply the finest, no-compromise full range loudspeaker system we know how to build.

Rhythm/Revelator Signature Project ...$Retired per pair.

Rhythm/Revelator Signature Center Channel $Retired each

Beautifully finished cabinets for the Rhythm Revelator and Revelator Signature - North Tempest are available directly from Lee Taylor and Company. Prices vary depending on the finish, starting at about $950 per pair.

North Tempest Loudspeaker system msrp $8,800/pair, retired

 The MD03 tower cabinet is also compatible with the Rhythm loudspeaker kit. North Creek Fascias are not available at this time.




Borealis Owner's Comments

Played one album then another and another until around 2am, just couldn't get enough. BorWalnut

They are ABSOLUTELY FANTASTIC. Bass tight and controlled, vocals and mid range sweet enough to bring you to tears and clean top with no hint of brightness. I have heard and felt things I never new were there.

The wee Plinius just eats the speakers, drives them very easily, no need to go over half volume any more.

Monday night was another long play session. I still need to get serious with the placement, but that will have to wait until I have all eight of my Big Toe Spikes.

To really describe these speakers is hard to put into words. Probably the greatest impression is how quiet they are, by that I mean when the music stops or goes quiet there is no singing cabinet or woofer, the music just stops. On some pieces its almost eerie.

Thank you for a great sounding and good looking piece of furniture, they are everything you said they would be.

I tell everyone about you and your product.


P.S. I just finished building a Borealis 9500 kit and I'm really happy with it, thanks for making these great DIY kits available and supporting the speaker builder community.  --V.W., Paris, IL



Almost a year ago a bought a borealis kit and I finished the project
just a couple of weeks ago. I am very happy with the result. It was very
difficult to me to buy a speaker kit after I listened to finished
speaker systems in the 2kUSD/pair range and became disappointed. But
finally I had to buy, since my old speakers got damaged. I based my
decision on your philosophy as provided in detail via the homepage,
despite the fact that I do not even have a TV set and all the home
theater stuff is not my world. Several emails have been very friendly,
helpful and reasonable.SteveSwirlyMaple

So let me give you a personal review, mainly to say "thank you" .
I have been looking for a speaker system especially suitable to listen
to music of the 16th and 17th century performed with period instruments
and singers. A typical "orchestra" consists of two to about twelve
individual players, each responsible for a separate voice.
Starting with physics, the limited bass spectral range of the Borealis
is absolutely no issue, since the deepest commonly used note is C, i.e.
the lowest note on the violoncello, that is 65Hz.
The Borealis system reproduces *any* instrument with a very natural
sound, and provides an outstanding spatial resolution. That is quite not
trivial after I realized that non of the finished speaker systems I have
listened to before has met both demands simultaneously. Renaissance
recorders seem to be very sensitive against spectral distortion, and
violins are critical as well. Both sound very natural. Individual voices
can be located by closing the eyes. A CD with lute music, which I
occasionally have heard for background, has converted to a hassle: The
lute player seems to sit in my living room and the breaks between the
peace, some of them played on different instruments, are too short for
beeing realistic! I never paid attention to that before. Despite my
awareness of the physical limit in the bass, I have listened to a
recording of organ music in a large cathedral where I attended many
concerts. The bass noted have not been received by the body, as
expected. But when the piece ended, one had an very clean spatial
impression of the decay of the sound! I know that I could add the 16'
and 32' octaves with your subwoofer system at any time.

When my first impression exceeded my expectation by far, I asked myself
if I made a mistake by not going for the unlimited version with the
matched speakers. My answer is no, because the present system is perfect
for my demands and I can use the extra few hundred euros for attending
real concerts, that is additional joy. It became obvious, that the
recordings itself are often not perfect, mainly in terms of volume
balance of the individual instruments, so listening to this type of
music has limitations which cannot be overcome with any speaker system.
But I mean this as a very personal priority and I am absolutely
positive, that any of the highly sophisticated "unlimited" speaker
systems you offer would be an excellent investment rather than expensive

So let me thank you again for a great kit which made happy and proud.

I just wanted to drop you a note on the outcome of my project.. First off, I am in AWE of the size of the 8 gauge inductor coils. It is truly hard to believe their size and installing them in Lee's cabinet got a bit interesting. They're in and they seem to be the anchor of the system.

They're currently breaking in a smaller room with placement following the manual. I have a question about the optimal tuning of the straws in the cabinet. The straw length is currently 1.25 inches beyond the end of the port tube. I'm not sure if this is right or not because Lee's tube is larger than yours. Is optimal tuning based on how comfortable with the sound?

Thoughts on the sound.
Thank you for such an enjoyable speaker! I find myself listening more and more to music, yes music. They're replacing a pair of B&W CDM7s which I now find average at best. The soft dome tweeter is much smoother and detailed than that metal dome tweeter. I'm hearing more and more detail that I never heard before (guitar plucks & singers taking breathes of air as they belt out vocals). I'm getting a much fuller, more robust, detail sound than I experienced previously. I thought my problem with the sound of the B&Ws was matching the cables to the amp and speaker. I was wrong. I don't believe those speakers could compete with these. I believe this so much so they're currently being sold. That should make a strong enough statement. I'm getting all of this wonderful music from a pair of 1 inch tweeters & 7 inch mid woofers without any lack of modest bass. IMPRESSIVE! As you say, crossovers and drivers are truly where you want to spend your money.

I now have a reference 2 channel system. Let's look into a HT system.

I thought I might get the Borealis to do double duty, HT & 2 channel. However I can't place them where I thought I could "squeeze" them in - home theater. So now a separate dedicated HT system needs to be sought. I think a better fit for a HT setup would be either Eska Mini Towers &/or Okara II-Cs on stands due to
room constraints. As before I'm interested in upgrading to quality all the way around. If there are ways of "maximizing" a speaker I'd like to explore those options. These might include going to a Revelator tweeter or upgrading the X/O beyond normal upgrades listed on the site. Any other X/O upgrades you'd recommend to the caps? prior to buying the Borealis you indicated 10 AWG coils would be a $90 upgrade. I believe this would be good for the Eskas.

Best Regards, -Gary


Just a quick note to say that I got my Borealis D28 project set up and running with about 40 hours on them now. All I can say is Sweet, very, very Sweet!

Thanks, Tyler R.

BTW - These are the strangest speakers I've ever owned. I do a lot of amplifier mods and like to listen to the results, but the Borealis defy analysis! I can no longer listen to my equipment - I can only listen to the beautiful music coming out of the speakers (wherever they are - when I close my eyes I can't find them). Still trying to get used to this - thanks :)

 -James W.

Hi George,

I'm writing to let you know that I am very pleased with the Borealis. I have finally broken them in- a friend brought over a rave album (Fluke) which at first I was worried because of the amount and frequency of the driver excursion but went ahead at full throttle for 8 hours (I left the house) and when I returned they definitely sounded better. I forgot how much pleasure there is in listening to music (not rave) through quality speakers. I am now considering the Vision for my future project. Thanks again.

Erik I.

p.s. - Lee Taylor's cabinets are perfect.


> Hi George,
> I purchased and constructed your Borealis speakers 2 years ago and
> WOW! Break-in required and then let the tunes begin. Couldn't be more
> amazed. I am driving them with a low quality Sony receiver with MP3's
> from my Macintosh and the sound is incredible....
> Thanks again for getting me started,  -> Douglas E.


Lee, the speaker cabinets arrived today. First, they are heavy! Then I
unpacked the first one and all I could do was to stand there and and say
"WOW! Look at that! It's the most beautiful thing I've ever seen in a
speaker cabinet. Its beautifully made, everything just right, what a great
piece of work!" Lee, I am very thankful for the craftsmanship of my
cabinets and I thank you for such beautiful work. Your packaging is very
nicely done, too. I can't wait to get it all assembled now and begin to
hear great music. Signed: a very happy customer, Craig K.

The Borealis is getting better all
the time, its going to be an excellent speaker, perhaps the last I'll ever
need to buy (although my wife would never believe such a statement). -Craig

Hello George Yes its John B. from Sydney Australia.I have implemented all
your suggestions for getting the best out of my speakers.As far as the base
response is concerned it is now just perfect.George they are so good it's almost
Send one of your the staff out to buy a copy of SHOWCASE Minnesota Orchestra
no RR-907CD. Play number 10 track Candide Suite By Bernstein. Just fabulous. Now George
if there is anybody that comes upon your website in the Sydney area,& wants to listen
before buying a kit from your company, I would be happy to have them stop by &
listen to my speakers, provided they come through you first.
Regards  -John

 Hi George,

Just wanted to let you know I'm thrilled with the Borealis. The midrange has opened up and they sound superb. Played around with the positioning there's certainly a sweet spot. Swapping the speaker cables over to the more transparent Furukawa seemed to help as well .
I still haven't made the stands and they're sitting on chairs at the moment.
I presume they'll only get better with time and steel stands.

Thanks for the musical insight! -Murray


Rhythm Owners Comments

Update up completed North Creek Rhythms. They sound very cool. A guitar player was over last night. As he was sitting in the sweet spot he suddenly exclaimed, "I can hear the picks!" He had been drawn in completely by an Eva Cassidy Cd then he suddenly realized he wasn't listening to live music.
The voices are clear all the way up into the loud high notes sung by Joni Mitchell. The cymbals sound like cymbals not just brassy noise. Also Linda Ronstadt's voice was clear through her entire range.
Other equipment Denon 2900 player and Denon 3803 prepro.
Dreaming of a Musical Fidelty 308 series power amp...... BillImage19


I was a bit nervous spending so much on speakers I had never heard before but as it turns out these are the best sounding speakers I have ever owned or listened too. Ive only logged about 60hrs on them so far but hey just keep sounding better and better. One of the first things I noticed about them is that no matter what volume they are played they sound great and have low end detail at the lowest volumes. Keep up the great work. I'll be purchasing more North Creek speakers in the future and I WILL tell anyone and everyone about the these great speakers.
Here are some pictures of my finished cabinets. I have the plinth's made and ready to install once my listening room is done.  -
John G



Thanks you for the speedy reply and clarification; I hope CES went very well for you. I have had the speakers up and running for a little over a week now and I believe that I may have finally gotten them "locked in". Almost each day I was testing them at various distances from the wall and different tilt angles. My roommates didn’t want the speakers out very far into the room but I’ve managed to consistently move them out to a point we all can live with, close to 2 feet from the back wall. Unfortunately the layout of our room restricts us to ~6 feet of listening distance but the frequency range seems more balanced in this configuration. One interesting note: I was adjusting the tilt the night before last in an effort to get the image up a little higher. I sat down to have a listen and noticed immediately that the speakers were at quite different angles of tilt, and yet the sound (it was a Radiohead album) had a floating characteristic across the soundstage that wasn’t there before. Needless to say they are still like that and I can’t bring myself to adjust it anymore, lest I lose that quality. At this point I am very happy with the sound; the level of detail within and the distinction between different instruments is very impressive. My only quibble is that I would prefer a tad more fullness in vocals and guitar strings, but it may be caused by my room and/or the other major point I want to bring up, my processor. Right now I am using a decidedly midfi Onkyo receiver (an abomination, no doubt) and I get the feeling that it is holding me back. Eventually I will finish a diy amp I am working on that should be able to do them justice, but I will probably be stuck with this processor for another year or two. In any case, I look forward to eventually hearing what they can do with good electronics backing them up. One last note, last night I put on the Jurassic Park III dvd to see how they could do for home theater. Man alive!! The low bass these speakers put out is just amazing for their size. My roommates had to reign me in several times on the volume control but I have never heard dinosaurs like that before; it wasn’t only the bass, but there was so much detail in the various grunts and roars that made their size very palpable. Thank you George for providing such an excellent product at a very respectable price. Rest assured I will return to you when it comes time to add on surround and center channels, and I have appreciated your quick replies to my questions.

RegardRhythmAngledFasciaTopViews, -George W.


Hello George

I have made the Rythym Revelator Signatures about 2 years ago and find them to be quite excellent in comparison to commercially available brands here in St. Louis that were 2 to 4 times the price..... Thanks for any suggestion and many nights of enjoyable listening.



Hi George,

I just wanted to say thank you for designing such a magnificent loudspeaker.

I finally assembled them over the weekend and I am blown away by their
musicality. I still have a little tweaking to do with room placement, port
tuning & stuffing, but despite that I am absolutely joyed with them. I could
go on & on about the sound, but you already know how they sound since you
designed them!

Attached is a pic of them complete.Image20

Thanks again, -Andrew B.


Hi, just wanted to drop you a note, and tell you that I completed my rhythm revelators. I could not be happier with my purchase! I have been in this hobby for a long time, and this was my first time building speakers, although I have always wanted to. I did alot of research before I bought my kit, and your companies designs, and innovations are the ones that caught my attention. They took alot of time to build, but I took my time ,and did a really good job on the cabinets. They sound incredible!! as good as I had hoped, and they are not even broken in yet. They rival many speakers at four times the price!! Anyway, just wanted to thank you again for making me believe that a set of speakers this good, could be made by someone with common sense, and who is good with there hands!! I am very interested in the thunder subs, and would like to integrate them into my rhythm system. Can you tell me if this sounds like a good Idea, and what is the best way to do this? I was hoping to do one per side,, I really like alot of bass is certain tracks, and have a very big room.

Best regards,,jon a.

Dear George,

My Rhythms are well broken in now and sounding great! I was able to take them to a large DIY audio meet this past weekend and everyone seemed quite impressed, even though there was neither time nor space to really set them up properly. One thing I particularly enjoy with these speakers is the bass. They seem to have the perfect balance for both HT and music and it suits my tastes perfectly. I have been considering adding in a subwoofer, since I watch a lot of movies and would like greater extension and greater spl capabilities on tap. I’ve taken a good look at your subwoofer offerings, but you don’t seem to carry exactly what I’m looking for so I was considering coming up with a separate design. I was wondering what the Qtc of the Rhythm cabinet was, so I could try and match the sound as closely as possible.

Thanks again and do let me know if you currently have any more sub designs in the works, particularly with a Vab < 120L and ~112dB at 20hz capability in a large room.

Kind regards, -George W.


I am glad you are enjoying them so much!

Which DIY event, may I ask?

The way to build your sub is to use a pair of Thunder's. This is 110dB without clipping and will reach 112dB no problem.

For a very large room, I suggest you consider stacking the Thunder's (2 woofers + 2 PR's per side). This was their original intent, and in this configuration 116dB clean is possible.

Thank you! --George CheungRhythm


I just realized that I never sent you a picture of my finished project.
Well here are two showing the figured walnut veneer. I can't tell you how much I love these speakers. I am so impressed with the imaging they have. The midrange is so detailed and although I was a bit skeptical of the low end at first I really happy with the fullness they project. It a while to break in and now everyone who hears them is very impressed.

Now the only problem is I have to upgrade my electronics to match the beauty of these guys.

Thanks again for all your help.  -Jeffrey L.


First, I must tell you that I finished building my Rhythms about 10 months ago
and the 2 channel sound they produce still amazes me. Thanks again for the
outstanding speakers.

Now, the reason I'm writing. I have a couple of questions.

Two years ago I purchased a Poseidon subwoofer from you. With the purchase of
the Rhythm speakers and Okara C for my home theater setup, I feel that I am
lacking in the subwoofer area. The room I'm using is 2,600 cu ft. and I feel
the Poseidon, while an outstanding sub, needs some help in the home theater.
Now for my first question.
Should I add another matching Poseidon or would a Thunder subwoofer integrate
with my exsisting Poseidon? I like the look of the Thunder as it would be
built to match the Rhythms'look.


While talking to my 15 year old son about what he would like for Christmas this year, he stated that he would like to build his own set of North Creek speakers with me!!! I couldn't be happier.
Question #2
For his first project, I was thinking about the Echo monitor. Do these speakers require a sub or will they be OK by themselves?

I've got the bug to build some more speakers and am waiting for your reply.   -Tom D.

P.S Attached is a picture of my Rhythms and Poseidon.

Dear North Creek;CU_Rhythm_System

First I must tell you that I have completed the Rhythms with the Kevlar Scan speak drivers, and I have 150% satisfaction! Broken in, every thing as promised in performance. I have a cabinet maker that made a very unusual alteration cosmetic to the cabs you suggest: Stunning in appearance and performance. I will be sending in a hand letter to George, and will toast him and his Rhythm Achievement. Yes- Pictures WILL follow as they are stunning. Yes, I will be building more as soon as my old gear moves on E-Bay. LOL.   -Alan Z.


I have completed the single Rhythm I ordered late last year as a center
channel configured to fit in my room/cabinet. Some photos are attached. I
built the original Rhythm 9500's about 5 years ago. I built the cabinent
with the same volume, fascia width, as the original cabinents. The front
panel has about a 6 degree angle built into the cabinent and adjusted
further with the Big Toes. Previously, I had a MTM with Seas 7" drivers of
my own design. The only way it worked at all was to preserve the vertical
position, otherwise the side-to-side sweeps gave you way too much timbre

I expected the Rhythm to be better, but it was "way-better". The blend of
timbre from calibration white-noise to DTS concert videos is now essentially
perfect compared to what I thought was acceptable before. The image blend
projected by this mounting position dictated by TV/cabinet is still very
satisfactory. Thanks for the excellent design and kit quality.

Regards;  -Billy B.

Hi George, I don't know if you recall but I had purchased two systems from you a while back. The Borealis unlimited for myself and the Rhythm / Thunders for a friend. They are both up and running and sounding great. Many stay up late nights just like you said on your web page, listening to lots of different music, that just sounds amazing now. Both of us are very satisfied with the products you designed and now have the itch to start building more. But as our luck would have it you are now discontinuing your DIY outfit. I do have one regret and that is that I didn't order a pair of Thunders for myself. They are the best sounding subs I ever heard. Well thanks again for designing such great products and taking the time to answer all of our emails. If you ever decide to have some more DIY projects, come across a pair of thunders, or have a sale on some products please let me know, like I said we have the itch. I have included some photos of the 3 Borealis but don't have any of the Rhythms / Thunders as of yet.

Thanks Michael D. A.