17 June 2010
JR “Modular Pro Monitor”
$2995/pr Standard Monopole, 1 piece/channel
$5995/pr Vertical Offset Bipole, 4-pieces/channel (upper box, stand, lower box, pedestal)
Upper Box (Monopole or Bipole): 14.75″ x 10″ x 11.75″ (H x W x D)
Upper Box Net Weight: 28 lbs
Lower Box (Bipole Only): 11.75″ x 14.75″ x 10″ (H x W x D)
Tweeter, all: 28mm diameter silk soft dome
Midbass, all: 17cm, composite cone, 75mm voice coil, solid cast aluminum frame
Power Handling Monopole: 130Wrms, 1kW 10ms
Power Handling Bipole: 260Wrms, 2kW 10ms
Sensitivity: 88 dB monopole, 89 dB bipole
Input Impedance (no impedance peaks above 100 Hz): Monopole 8-Ohm nominal/5.3-Ohm minimum. Bipole either 16-Ohm nominal/10.6-Ohm minimum or 4-Ohm nominal/2.7-Ohm minimum (see text)
Amplifier Requirements: System has no impedance peaks above 100 Hz. An Atma-Sphere 30W OTL was a match “made in heaven”, the best interface I’ve ever heard. Played any desired level in a 3k CF room, by significant margin louder and more authoritative than a perfectly running Plinius SA-50 Mk3 pure class-A SS amp (the 60 lb SA-50 is no slouch by any measure)
Front view
Front view
Front view
Front view upper box
Front view lower box
Front view
Rear view
Rear view upper box. The upper posts go to the rear tweeter only. The lower posts go to the front-firing XO then to the midbass/tweeter.
Rear view lower box. The posts connect to the rear-firing XO, which connects to the rear midbass. The rear-tweeter wires exit the port, then hide in 1/2" O.D. split loom tubing secured to the back of a vertical stand support, then the wires exit the tubing at the top and connect to the tweeter posts of the upper box.
Front and rear panels of upper box are raised 1/16" with beveled edge. On the lower box only the rear panel is raised.
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Philosophy and Evolution
Enter a Rare, Exemplary, Artisan Standmount
Around 2006 my taste changed from large floor standing speakers to standmount (or “bookshelf”) type. I owned what I thought was a superb pair of exotic standmounts with external passive crossover (XO) and planar mids and tweeters. In 2007 I met a professional journalist, recording engineer and singer of classical French music. We shared similar taste in audio components so I asked for the name of his favorite standmount speaker. “By a wide margin” he preferred the French ASA Pro Monitor designed by a French recording engineer. ASA stands for Atelier de Synergy Acoustique or Workshop of Acoustic Synergy in English. The US importer Walter Swanbon (a kind and wonderful professional) of Fidelis in New Hampshire sent me a matched pair of ASA Pro Monitor with return privilege. I preferred and kept the ASA.
In 2008 Walter said new Pros would cost “$6500-$7000” MSRP (the effects of inflation and exchange rates). I supposed I might find buyers even at the high price of $7k. I pestered Walter for new Pros for resale.
The ASA Pro Monitor is the reference speaker for Vince Galbo, National Sales Manager at MSB. 6 Moons’ glowing review of the entry-level ASA Monitor Baby (two steps below the Pro) is here. Stereophile Magazine editors Sam Tellig and John Marks comment on the ASA Pro here and here. A pro DJ/recording engineer in Mexico loves them here. It is telling that all the above fans are full time audio and/or music industry professionals. The ASA Pro remain my favorite production standmount speaker.
What do ASA Pros sound like? They sound like a small-scale version of the late-80s through mid-90s Duntech Sovereign 2000 6-1/2′ towers with symmetrical vertical array. Those familiar with the Sovereign may agree that “dramatic” (in the best possible sense, not fatiguing or distracting) is an excellent description of their sound. The ASA convey some of the Sovereign’s drama, tonal balance and emotional impact. Tonal balance and overall presentation is also similar to the Shahinian Obelisk but with tighter image focus and smaller radiation pattern. Compared to Harbeth’s current monitors the ASA Pro have more drama, involvement, a fuller midrange and larger stage, with no downside. (BTW, I love the Harbeth sound.)
Enter A New Proprietary Design
Circa 2008/2009 I auditioned the AudioKinesis Dream Maker with (apparently) proprietary design technology from Duke LeJeune of Preston, ID. Duke calls the technology “vertical offset bipolar.” Bipolar = front and rear firing drivers both in positive acoustic and electrical polarity. Vertical offset = the front and rear firing midbass drivers have different vertical heights (or “offset”) relative to the floor; the offset is maximized within the limitations of other design considerations.
I was hooked on the unique performance characteristics of Duke’s technology. Those qualities were easily identified and isolated because I am very familiar with the Jazz Module, a monopole version of the Dream Maker. The book Music, Physics and Engineering by the late Dr. Harry F. Olson of RCA Labs includes polar radiation graphs of many musical instruments. None of the instruments distribute sound in a monopole pattern; all patterns are modified omnipolar. (Sidebar: my wife’s cousin’s husband is in his 70s; he engineered nuclear power plants for GE and educated other nuclear engineers around the world. After scanning Olson’s book in 2007 he declared it a gold mine with many equations he wished he had found earlier in his career. He wrote a textbook in his field, recently published.)
Omnipolar speakers reflect too much sound off the room’s walls, blurring image specificity. Reviews and my auditions of the legendary and uber-costly German MBL Radialstrahler confirm this. The polar radiation pattern of Duke’s vertical offset bipolar technology is about ½ that of an omnipole, with better image specificity and a preferred radiation pattern. (I surely love the MBL properly setup in a humongous room that no one I know personally can afford.)
Several decades of experience lead me to recommend auditioning Duke’s or my speakers with vertical offset bipolar technology. They offer unique performance advantages available by no other known method. All the many comments I’ve read about the Dream Maker are positive, including TAS editor Robert E. Greene who bestowed them his coveted 2008 Golden Ear Award.
Why did I not purchase the Dream Maker? My DSA 1.0 subwoofer link explains my preference for standmount speakers with a multiple subwoofer array. In addition, I am among a good portion of audiophiles preferring phase-coherent/phase-correct crossovers, meaning all drivers (above the subwoofer range) are in positive acoustic and electrical polarity. Theil, Vandersteen, Verity Audio, Sonus Faber, and the old Duntech and Dunlavy are some speakers meeting this criteria. (Sidebar: such designs reveal absolute polarity better than non-phase-coherent/non-phase-correct speakers.) The Dream Maker do not fit this description even though they are among my favorite speakers.
This leads us back to the wonderful ASA Pro Monitors. What to do? I had to have Duke’s vertical offset bipolar radiation pattern. Adding this feature to the ASA Pro Monitor seemed like speaker Nirvana.
The King is dead! Long live the King! Or…enter a new cloned speaker with upgrades…
So…Duke and I cloned the ASA Pro Monitor and added Duke’s vertical offset bipolar feature. It is christened the JR “Modular Pro Monitor.” This speaker is currently available by special order only for $3k/pr USD in monopole version, $6k/pr USD in bipolar version. Each order is custom and delivery takes ninety days.
Overview
The name “Modular Pro Monitor” is because it is a standard standmount (or bookshelf) monitor upgradeable to a “vertical offset bipole.” Standard (monopole) monitors have the rear tweeter hole precut and second (upper) set of binding posts for the rear tweeter; the tweeter hole is sealed with a removable cover. Adding the rear tweeter requires only removing three cover screws, attaching two push-on terminals to the tweeter, and securing three tweeter screws.
Modularity allows buyers to purchase a regular monitor then upgrade to the vertical offset bipole. Modularity also allows bipole owners to remove the upper box to function separately as a monopole monitor, such as for location recording or other temporary use.
The above features are unique.
In bipole form one channel employs two enclosures. A 15” tall stand elevates the upper box above the lower box. The upper box front panel secures (from the top down) one each midbass and tweeter; its rear panel secures one each tweeter, port and input terminal board. The face of the lower box is finished the same as all side panels. The lower box rear panel houses the rear firing midbass, port and input terminals for rear-firing drivers only.
2-Smaller Boxes vs. 1-Larger Box
There are several good reasons for specifying 2-boxes per channel rather than one larger box. The rear firing midbass required a minimum width to depth ratio. One larger box would have be unnecessarily wide for the front-firing drivers, likely decreasing image/stage performance and its ability to disappear as a sound source, especially at closer listening distances. Smaller box panels vibrate less and have less panel output. The resonant wavelengths associated with large box dimensions can become so long that damping materials are ineffective. Finally, two boxes are required for the modularity feature.
Drivers and XO
The drivers are high quality w/ high power handling. All drivers connect in positive polarity. The front drivers physically overlap to minimize lobing. A European who is one of the world’s most distinguished and successful speaker designers, with over thirty years experience (who shall remain nameless), consulted on the selection of crossover components. Someone from California who personally tested in his self-built premium tube system, on his own custom speaker design, about thirty of the world’s best capacitors, contributed toward the capacitor choice.
The major value capacitor for all banks is a paper in oil type for maximum transparency and musicality. Such caps provide exemplary audio performance for this particular application. In this application, the chosen caps are extremely detailed and portray incredible nuance, yet they completely devoid of harshness, ringing, and fatigue. Tremendous time is spent acoustically testing every capacitor in the front-firing crossover for phase/polarity. A special and costly series tweeter resistor is inverse heat-sensitive to maintain a constant crossover pole. Lacking this feature the pole shifts when the tweeter voice coil temperature rises. The series inductor on the front midbass is litz wire for maximum transparency. All resistors are wire wound.
Duke also engineered a parallel (no series circuit path) EQ filter to flatten the impedance curve above the bass range. Performance improves with all amps, OTL the most, followed closely by transformer coupled tube amps, then a moderate upgrade with SS amps.
Modularity requires separate crossovers for the front and rear firing pairs of drivers. The separate bipole crossovers connect either in series (16-Ohm nominal/10.6 Ohm minimum) or parallel (4-Ohm nominal/2.65 Ohm minimum). Series operation is suited for all tube amps, especially OTL, and low to moderate current (most) SS. Parallel operation is only for high-current SS amps. As a standalone monopole monitor the upper box is 8 Ohm nominal/5.3 Ohm minimum. The upper box houses the XO for the forward firing drivers; the lower box houses the XO for the rear-firing drivers. Two conductors exit through the port of the lower box, route up through 1/2″ diameter black plastic split loom tubing attached to the back of a vertical post on the stand. These conductors connect to a second pair of binding posts in the upper box to drive the rear-firing tweeter. These binding posts are unused when the upper box functions as a standalone monopole monitor.
Enclosures
In 2008 I read about a new combination of wood types to laminate for speaker panel use. Sound tests proved its usefulness. Laminating the two woods provide constrained layer damping. I chose 5/8” of each material for 1.25” total thickness. Later I discovered a famous speaker, one of my favorites, follows a variation of the same materials theme. Each speaker employs three panel materials, which minimize and broadly disperse resonance compared to a lesser number. In direct comparison audio performance was preferred vs. the ASA enclosure made of far more costly solid 1.25” finger-jointed Ovangkol. The laminate is heavier than predicted and heavier than the same volume/same thickness Ovangkol, which is very dense. I dropped the earlier plan to attach ¼” steel plate ballast to the base.
The upper and lower box share dimensions but are oriented differently in space and are constructed differently for their application.
The enclosure builder meticulously and laboriously laminates each panel individually w/ four solid 2×2 maple blocks distributing the pressure of two clamps. Each bare enclosure is about 26 lbs empty.
Stain and several coats of clear lacquer cover all external surfaces. The rear of the lower box and front/rear of the upper box are painted black, raised 1/16″ and have beveled edges. In the future these panels will be finished low-gloss and painted black/gray for a textured appearance. The enclosure builder specified the widest possible corner round while maintaining maximum joint strength, consistency, integrity, and longevity. The builder is a long time speaker-cabinet professional, taking great pride in his workmanship and attention to detail. He was an invaluable asset for such a complex project.
Amplifier Interface
An Atma-Sphere 30W OTL stereo amp was a match “made in heaven”, likely the best amp/speaker interface I’ve ever heard. It played any desired loudness in a 3k CF room, louder and with more authority than a perfectly running Plinius SA-50 Mk3 pure class A SS amp. Without the special impedance E.Q. circuit described above the OTL added an unpleasant and easily identified midrange peak at a bandwidth equal to the impedance peak.