North Manifest Loudspeaker System

North Creek Music Systems

Manifest

Ribbon Hybrid Loudspeaker System

Manifest Design Concept

The Manifest was conceived of as the next evolutionary step from our very successful North Creek Rhythm (North Acoustics Tempest) loudspeaker system. The placement constraint is free-field, that is, with the front of the loudspeaker around four feet from the back wall and a minimum of four feet from the side wall. Bass tuning is full range, so that like the Rhythm, the Manifest would not require a subwoofer to obtain both exceptional deep bass and very high SPL's.

Designing they system around the Aurum Cantus G1 ribbon midrange-tweeter determined the driver size; with a low crossover point of 1.3kHz, we were able to employ a custom 7" woofer built by Scan-Speak. Together with the optimal cabinet volume and fully tunable rear firing port, the Manifest is capable of solid, clean bass down to 29 Hz.

The resulting system sets a new standard in audio reproduction form a small footprint, medium sized MTM loudspeaker system.

Photo at right is the North Manifest in rainforest freindly Zebrawood veneer, courtesy of Lee Taylor and Company.

The Ribbon

Aurum Cantus developed the G1 ribbon midrange-tweeter to mate the extraordinary speed of a small ribbon tweeter with the upper midrange performance of the best dome tweeter. Up to the development of the G1, all other true ribbons on the market had a low frequency limit of about 3kHz, and also required high crossover slopes to perform their best. The Aurum Cantus G1 has a usable bandwidth down to 1.3kHz, and because it also has exceptional excursion limits, it can be used with a lower order crossover slope and still provide excellent performance.

The G1 ribbon diaphragm itself weighs only a few milligrams; a fraction of any similarly sized dome. Suspended between parallel rows of Neodymium magnets, the diaphragm is immersed in a magnetic field that is both incredibly strong and uniform up to the excursion limit. The combination of high field strength, a nearly massless diaphragm, and exceptional excursion limits results in a tweeter with extraordinary speed and a level of clarity that is unsurpassed.

The Woofers

Choosing a woofer to match the incredible speed of the Aurum Cantus G1 Ribbon required considerable effort. In order to satisfy our deep bass and high SPL requirements, it was clear from the outset that no "off the shelf" driver would suffice. North Creek's long association with Scan-Speak lead to the decision that as the patented SD-1 motor reproduces the cleanest bass from a mid-sized vented system, bass that remains clean and tight even at very high volume levels, it would be Scan-Speak woofers as the core of the system. Scan-Speak woofers are also nearly indestructible, an important concern for a woofer that will be driven to its limits for years to come.

We tested the standard and variations of the Scan-Speak 18W series, and in the end developed a custom, more powerful version of the 18W motor and specially made paper-carbon fiber composite cone. The new driver offers a very low free air Q and fundamental resonance of 31 Hz, yielding exceptionally tight deep bass in a small cabinet. Because the motor is stronger, the driver speed is increased, making it a perfect match for the G1.

The Ambience Tweeter

Because the Aurum Cantus G1 ribbon midrange-tweeter is 6" high, it has a very narrow vertical dispersion window. What this means to system design is that the nearfield frequency response will not suffer from early floor and ceiling reflections, improving soundstage depth and image focus. However, the ambient field, created by late reflections from all boundaries, will lack high frequency sparkle. Therefore, the Aurum Cantus G2si Ribbon Tweeter was added to the system, mounted on the cabinet rear with the ribbon oriented horizontally. This configuration limits the ambient high frequency horizontal dispersion while maximizing its vertical dispersion. Combined with the late reflections from the G1, a uniform ambient field is created.

Voicing, Bass Alignment, and Crossover Design

Loudspeaker designers have debated for decades what is the most critical aspect of loudspeaker design; cabinet design, bass alignment, crossover slopes, phase linearity, etc. All of these elements are important to the success of the finished design, and all contribute to the most critical aspect: Voicing.

Voicing is the process of precisely balancing a loudspeaker's deep bass weight, low end punch, lower midrange robustness, midrange liquidity, upper midrange openness, and top end sparkle to create a system that is homogeneous in character from top to bottom and reproduces all forms of music and voice with the correct harmonic content.

Voicing is also the most difficult aspect of loudspeaker design, simply because it is purely subjective. Getting the voicing exactly right requires months in the listening room.

We have found that with the Scan-Speak 18W series of woofers, the best sounding bass alignment is the QB3. It is very dynamic, well controlled, with a lot of punch and excellent timbre. It also requires a cabinet volume of only 44 liters, keeping the Manifest footprint small.

A flat bass-lower midrange-midrange range is achieved by balancing room gain, the Scan Speak woofers’ natural rising response, and the 6dB response step by implementing a progressive third order low pass filter. This unique type of crossover begins with a very soft 3dB per octave electrical slope for nearly two and one half octaves though the entire midrange, then becomes 18B/octave as the 1.3kHz crossover frequency is approached. The resulting acoustic response is flat from the low frequency measurement limit to 1060 Hz, 6dB down at 1.3kHz, and continues to roll of smoothly at 18dB/ocatve as frequency increases.

The Aurum Cantus G1 ribbon mounted in the Manifest cabinet exhibits nearly perfectly flat frequency response above 2kHz (1). Through the crossover region, the ribbon output is gently rolling off at 6dB/octave. Therefore, a simple second order high pass filter is employed to reach the 18dB/octave high pass slope, 6dB down at 1.3kHz.

With all drivers connected in positive phase, the Manifest measures +-1.25dB from the low frequency limit to 20kHz. The antiphase null is a full 24dB and there are no peaks in the antiphase curve, indicating perfect phase addition when all drivers are positive and perfect cancellation with the midrange-tweeter reversed.

The low frequency measurement is made via the close mic technique for both the woofers and the port egress, then correcting for the cone and port area ratios. This curve is then spliced to the anechoic frequency response curve at its low frequency limit. This is the overall system frequency response, measuring and excellent 36Hz to 20kHz +-1.25dB, with a low frequency limit of 31 Hz. System sensitivity is 92dB @ 2.83 Volts, 1 meter.

System impedance is plotted below, with the ambient Aurum Cantus G2si switched on. Impedance minimum is 3.6 Ohms at 360 Hz, and the maximum is 20 Ohms at 1.1kHz. This impedance may be difficult for some amplifiers to drive, therefore an impedance "twister" circuit was developed. With the twister in place, system impedance is 4.80 Ohm +-1.25 Ohms from 70 Hz to 20kHz, easily driven by both solid state and valve electronics.

Sound Quality

The opportunity to use a true ribbon midrange-tweeter from 1.3kHz on up sets a new standard in upper midrange speed and transparency. The sound is so light, detailed and remarkably complex. The combination of the front facing Aurum Cantus G1 and the rear-mounted G2si creates layers of soundstage and pulls out nuances in the ambient field that are so convincing they are almost magical. The extreme top end seems to shimmer, clear as glass and without any hint of sibilant emphasis.

Likewise, our custom Scan-Speak woofers - driven by an enormous double-stacked magnet structure - are fast, incredibly clean and extremely dynamic. Lower midrange though the deep bass is reproduced with richness, texture and timbrel accuracy that matches the G1 in both speed and character. Listening to Jean Luc Ponty "Rhum "n "Zouc" (Putumayo 104), the amount of texture revealed in the African hand drums is magnificently juxtaposed with the violin.

The Manifest loudspeaker as a complete system possesses the homogeneity of character that one can get only from a well designed two-way. Two excellent recordings are Janis Ian "When the Silence Falls" (Putumayo PUTU128) and Rebecca Pidgeon "The Word Around Town" (Chesky CHE10A) where the vocal range covers all drivers and the harmonics are constantly moving across the crossover frequency. With the Manifest, there is absolutely not hint of the crossover discontinuity and the harmonic balance stays stable. Likewise with the Fairfield Four "Standing in the Safety Zone" (WB 9-26945-2), where the fundamentals and lower harmonics are all reproduced by the Scan Speak woofers, and the upper harmonics by the Aurum Cantus G1 ribbon. There is no sense of any transition.

The Manifest is also a fun loudspeaker to listen to. CD after CD, regardless of the era or gendre, the Manifest delivers with it perfect balance of an aggressive low end, fluid midrange, crystal clear top end and exceptional dynamics.

Driver and Crossover Component Quality

Like all North Creek Signature drivers, the Aurum Cantus G1 and G2si ribbons and the custom Scan-Speak woofers are broken in for a period of 60 hours. The extended break-in assures that the drivers will perform properly "out of the box" and for years to come. The drivers are then serial numbered and hand matched to +-0.25dB.

Obviously this is not an inexpensive loudspeaker. The G1 midrange-tweeters alone are nearly $1000 per pair. Adding the custom Scan-Speak woofers and Aurum Cantus G2is ambient tweeter and the driver cost exceed $2k.

So there is not point in skimping on crossover component quality, and in fact these drivers are so good that any compromise whatsoever is clearly audible. The Manifest gets only the very best.

The woofer section consists of 8 AWG inductors, Zen metallized polypropylene film capacitors Cascade-Bypassed by Crescendo film-foil capacitors, North power resistors, Lexx wiring, and all gold-plated connectors.

The midrange-tweeter network is built only with Cascade-Bypassed Crescendo capacitors, 10 AWG inductors, North power resistors, Tef-Flex silver wiring, and all gold-plated connectors.

The ambience tweeter network is built with a single Zen capacitor and 12 AWG inductor. Wiring is Tef-Flex silver and again all gold-plated connectors.

The impedance "twister" compensation circuit is constructed of a 24 AWG inductor, Zen metallized polypropylene capacitor and North power resistor. Wiring is OFHC copper.

The loudspeaker is bi-wired with our highest quality, heavy gold plated Big as Texas binding posts.

Like all North Creek loudspeakers, all crossover components are had matched to 1% before assembly. The networks are hard wired point-to-point, where all connections are made by a crimped cold weld and soldered with the best Kester silver solder. All networks are tested for perfect performance.

Availability

The North Manifest Loudspeaker Project

Consists of "Perfect Quad" Scan Speak 18W8545SC woofers, "Perfect Pair" Aurum Cantus G1 and G2si ribbons, fully assembled and tested crossover networks as described above, bi-wired with heavy duty gold-plated Texas binding posts, Big Toe and Very Big Toe spikes, port tubes, gaskets, DuPont Dacron stuffing, etc; everything required to build the loudspeaker system except the wood.

North Manifest Project .....$3,899.00 per pair

North Manifest System ....$ retired

With cabinets by Lee Taylor and Company, most veneers, fully assembled, broken in and thoroughly tested to be within 0.25dB of our reference system. Includes shipping crates, grilles and plinths. Shipping is via freight truck, FOB Thendara, NY.

Beautifully finished cabinets are available in a variety of veneers are also available separately directly from Lee Taylor and Co.; www.TaylorSpeakers.com, or email Lee directly via LeeWTaylor@verizon.net

Photo at left is a North Manifest in Wild Mottled Makore veneer.

Cabinet plans are available through this link.

North Creek Music Systems, PO Box 1120, Old Forge NY 13420

Info@NorthCreekMusic.com, Sales@NorthCreekMusic.com, fax 315-369-2500

AV Loudspeaker Kits: Echo Family | CM-7 Family | Okara II Family | Fiesta y Casita | Vision Family

Valve-Specific Loudspeaker Kits: Ariel Family | Catamount | Prometheus HO/T

Full Range Loudspeaker Kits: Rhythm and Borealis | Pegasus

Full Range Ribbon Hybrids: Manifest | Prometheus | .A.R.T. Metro

Subwoofers: Poseidon Kit | Thunder Kit

Loudspeaker DIY: Drivers | Crossover Components | Publications | Component Price List | Coil Price List

Designer’s Comments

Undertaking an evolutionary step to the North Creek Rhythm required considerable thought and effort. The Rhythm is undoubtedly the most successful loudspeaker kit in history, also by far the most widely copied. Since its last major revision in 1997, the Rhythm has undergone only minor changes and upgrades and these were due to changes in Scan Speak’s production or advances in our crossover component technology. Also the fact that for a small footprint and relatively inexpensive loudspeaker system, the Rhythm sounds incredibly good.

After auditioning an Aurum Cantus ribbon driver custom made for Red Rose Music in early 2003, there was no question that North Creek would explore incorporating the Aurum Cantus ribbons into the North Creek product family. In May of 2003 we secured samples of the ribbons and I went to work in the wood shop and the lab, our first product targeted for September of 2003. Working with Aurum Cantus, North Creek secured one of only two distributorships in North America, beginning in September of 2003.

Selecting a woofer was considerably more difficult. The Scan Speak 18W8545 in a QB3 cabinet has the best low end of any 7" driver on the market, also enormous excursion and the ability to stay clean when played very loud. It is also virtually indestructible; we have had only three fail in the field, a failure rate of a remarkable 0.11%. We tried many drivers from several sources, but in the end it was narrowed down to a custom 7" built with the Scan Speak SD1 motor and 8545 cone, or the SS 18W8530K00. In the end, we went with the custom driver, labeled the Scan Speak 18W8545SC.

Among reasons for this decision were that to minimize our foot print, a small vented cabinet was required, and the 18W8545SC has both a very low Qts and a very small Vas. The 18W8530K00 requires three times the cabinet volume (nearly 120 liters) and has a higher Qts, around 0.45. This makes it perfectly suited to large vented boxes, transmission lines or acoustic suspension, but it will not work in a small vented box.

Secondly, the original 8545 is absolutely flawless in the throughout the lower midrange and maintains character from the deep bass throughout the entire midrange. While the same can be said of the 8530 (and in fact the 8530 may be superior above 3kHz), it requires a much larger vented cabinet to do so. The 8530 in a mid-sized acoustic suspension cabinet did not obtain the combination of deep bass foundation and mid-bass impact that we easily get from the 8545SC.

Third, there is the sensitivity issue. With the custom 18W8545SC, we were able to obtain a system sensitivity of 92dB @ 2.83V, 1 meter. With the 8530, the best we could do was 90.5dB. Since the Manifest is intended to be compatible with SET’s, every fraction of a dB counts.

So the custom Scan-Speak 18W8545SC is the only – and best sounding – choice.

Design of this system took about five months, a little longer than expected because of the woofer selection issues. Crossover design was also extremely difficult as the transition region had to be perfect. The Aurum Cantus G1 is so fast that any inconsistency in the transition region was clearly audible as "slow woofers, fast tweeter". In the end, crossing the G1 out at its absolute low frequency limit allowed the woofers to keep up. Going a few Hz lower or using a small gauge inductor is out of the question; 10AWG is the minimum ¹, and bi-wiring with heavy speaker cable is mandatory.

Here we define the crossover frequency as the point at which the woofer and tweeter output cross, about -6dB acoustically. Were one to attempt to cross the Aurum Cantus G1 at 1.3kHz with a "text book" second order filter, it would not survive. The "textbook" electrical high pass filter frequency is actually 1890 Hz, as defined by the filter time constant 2p F=1/Ö (LC). It is the product of the electrical high pass transfer function and the G1's acoustic response that gives the -6dB point of 1300 Hz.

The rear ambient tweeter….. on the back, with the ribbon mounted horizontally. Originally this was a dome and first order crossover around 3kHz, but focus within the soundstage suffered compared to the system with no ambient tweeter. Experimentation proved that a higher crossover frequency and slope could add the "air" without compromising image focus. Controlling the horizontal dispersion pattern by employing the G2si ribbon, mounted horizontally, further improved the homogeneity of the ambient field. Undoubtedly, this technique will be widely copied and many will claim they came up with it themselves.

So, is the Manifest "perfect"? No. To be perfect, it would have a flat 8-Ohm impedance (instead of a nearly flat 5-Ohm), go to 20 Hz (instead of 31), and of course be invisible. But for a nearly full range system in mid-sized listening rooms, driven by good electronics, it is very very close.

The Aurum Cantus G1 Ribbon is equally as remarkable in measured performance as it is to listen to. Shown below is the G1's impedance and frequency response curves, taken at 0.7 meters under anechoic conditions in a 2-pi environment. The measurement window is accurate above 300 Hz.

Studying the impedance curve, one can see only a hint of the fundamental resonance frequency, at 890 Hz, where the impedance rises to 7.23 Ohms. Above 1kHz, the impedance varies from a minimum of 6.65 Ohms at 2kHz to a maximum of 8.06 Ohms at 20kHz. An impedance curve this stable greatly simplifies crossover design.

The frequency response is also quite smooth and relatively flat, the usable bandwidth of 1.1kHz to about 18kHz with a gentle rise 4.5dB. The broad dip in the region around 2kHz also simplifies crossover design, as cabinet diffraction always creates a hump in this region.

Above is the Aurum Cantus G1 waterfall plot over a 4msec window, with a waterfall depth of -30dB. The first 0.5msec is the actual frequency response during the impulse, and the first decay slice takes place at 0.6msec.

What is of special importance is that the decay is nearly complete by 0.8msec, of an incredible 0.2msec after the impulse is turned off. Within 1msec, the ribbon diaphragm is completely back to rest.

All told, this is the best measured performance this designer has ever recorded.

There has been some debate over the audibility of employing large-gauge inductors in the shunt circuit of a tweeter high-pass network. In this designer’s opinion, those who state there is no improvement from say an 18 gauge inductor to a 12 gauge inductor, have never tried it. In particular, it is the clarity of the upper midrange that is significantly improved, especially at high volume levels.

Objectively, the reason for this is easily determined by examining the voltage plot of the high pass crossover network in the stop band. For second and third order high pass filters, below the frequency at which the inductors DCR is equal to the inductors reactance, the crossover slope become first order. This frequency is called the "secondary corner frequency", and is illustrated by the voltage plots below.

Here the secondary corner frequency is about 130 Hz, one decade below the G1's crossover frequency. The network attenuation is 29dB. An octave below the secondary corner frequency, the difference in attenuation is 6dB - equivalent to a factor of four in diaphragm excursion.

What this means to the tweeter is that below the secondary corner frequency, the attenuation of diaphragm excursion for a given system SPL (or input voltage) is limited only by the tweeter’s suspension.

For a dome tweeter, which is essentially a very tiny sealed box, excursion is also limited by the air spring behind the dome below the tweeter’s fundamental resonance… so the dome tweeter can "take it" for months or even years before breaking.

For a ribbon tweeter, however, this is not the case, and excursion is limited only by the stiffness of the corrugations of the ribbon itself. Ribbon overexcursion is not pretty. Generally, the ribbon will bow in or out, twist half-way around, lose its corrugations, and eventually snap. It also does not sound very good on its way out.

The larger inductor gauge lowers the secondary corner frequency. For a ribbon, the lower, the better.