Speaker Design Philosophy
A renown issue with cone and dome designs is that pattern size shrinks as frequency rises, and pattern size grows as frequency decreases. The pass band is the range where two drivers overlap. When two drivers in a pass band have different diameter (cone mid/dome tweeter), the size of the two patterns is continuously opposed. Such pattern distortion is contrary to nature, and humans have high sensitivity to it, perceived as a “box” or “shouty” effect. Panel speakers have other problems but not this one.
A well designed wave guide closely matches driver patterns in the pass band, and also has a more consistent pattern than any cone mid range and dome tweeter (hence the term “constant directivity” wave guide) .
All wave guides are horns but not all horns are wave guides. Some horns are prone to a “cupped hands” distortion. Lynne Olson is a prolific and well known DIY tube amp designer who also designed Ariel, one of the all time most popular DIY speakers. Lynne describes himself as having high sensitivity to cupped hands effect in horns, and yet he is one of AK's biggest fans, noting no such effect in AK speakers (see "Comments, Reviews.")
In some cases horns also have a reputation for causing listener fatigue. AK fans and owners state that AK's timbral presentation is opposed to typical horns, being pleasing, musical, natural, and transparent, inviting all day listening sessions extending into the night. One AK Zephrin 46 owner said it tended to minimize his tinnitus.
Duke tends to trade some of the wave guide's potential sensitivity in favor of smoothness, linearity and transparency. AK sensitivity specs are accurate, and more conservative than industry standards, falling about mid way between cone/dome standards and a typical horn. Except for as noted in certain rare model, all models are well suited to tube and OTL amps, with benign phase angle and moderate impedance. (OTL prefer more than benign phase angle; the higher the load impedance the better.)
Some of the world's most costly and legendary speakers employ horns and wave guides. If you've not considered an affordable, ultra high performance wave guide loudspeaker, we welcome you to learn about them and consider becoming another happy AK loudspeaker owner.
Power Handling and Maximum Output
Typically, with a cone/dome loudspeaker, the closer one approaches its maximum input capacity the greater is the magnitude of compression. The system volume also acts like a "compression" control. At peaks near maximum input, cone/dome speakers compress about 10 dB. Conversely, under the same conditions, AK typically compress 1 dB. The difference in presentation is welcome. Dynamic peaks are more lively and lifelike, more closely mimicking what we hear in live music.
But there's more to the story Re. dynamics. One might reasonably suspect that each 3 dB loss of speaker input sensitivity is easily fixed by simply doubling one's amplifier power. In real world terms it doesn't work out that way.
Even in cases where two different amp/speaker combinations have the same peak output capacity on paper, the higher sensitivity speaker sounds more alive and lively (only in the best way) at any average listening level, from the lowest to the highest. At the lowest average listening levels a cone/dome typically tends to sound dull and lifeless, while the higher sensitivity speaker sounds engaging and enjoyable. Something to consider on those occasions when you don't want to wear headphones and you really want to enjoy listening with minimal environmental impact.
Wave Guide Types
For the front/main wave guide, AK employs either Duke's proprietary round poplar wave guide made to his specs (Gina), or SEOS (super eliptical oblate spheroid) rectangular wave guide, the latter being 10.5, 13.5, or 15.5 inches wide. The wider the SEOS wave guide, the smoother and more linear is performance at the perimeter of its radiation pattern.
Gina's round horn yields 90 x 90 degree pattern, while SEOS (SAY-ahs) horns yield 90 vertical x 45 horizontal pattern.
An inherent performance advantage with Gina is super high tolerance between the CD's exit angle and the horn's entry angle, yielding audibly less diffraction.
Acoustics: Cracking the Early/Late Arrival Conundrum
Few if any other speaker designers match Duke's knowledge and experience Re. the ideal balance between early and late arriving signals. Among other authorities on this subject, Duke is a rabid student of four eminent PhD's: Earl Geddes, Floyd Toole, Robert E. Greene, and David Greisinger. These individuals do not always agree 100%, but together they likely have the most reliable and extensive knowledge base on this subject. I encourage readers to research the bio and work of these four individuals.
David Greisinger proposes that the less early arriving reflected energy the better. DG has posted music recordings with vs. without early arriving reflected energy, in which the listener can decide for themselves.
For purposes of this disucssion, “early” reflected energy is signal that arrives less than about 10 ms after early arriving signal. (Sound travels @ 1125 feet per second x 0.01 S = 11.25 feet path length difference.) This is a simplification that must suffice for our discussion.
For domestic listening, there is universal or almost universal agreement that a high ratio of late arriving reflected energy improves audio performance. In a typical concert venue, more than half the perceived energy is reflected and late arriving. The most obvious and renown postive effects are increased pleasure, density, immersion, and envelopment. Spatial qualities improve in every aspect.
Toole states that properly delayed reflected energy gives listeners a second look (in real time), which even improves pitch perception. Years ago, after I mentioned Toole's findings to an amateur audiophile, he replied, “My speakers do not distort pitch.” To date there is no test spec for loudspeaker pitch distortion, but our experience indicates Toole is correct, and a loudspeaker “pitch perception” test would be a good indicator/predictor of performance. IOW speakers do vary in the degree to which they accurately portray pitch on program material. Properly delayed and properly processed reflected energy increases pitch perception, which can make music that was boring sound interesting and pleasurable. Music with complex pitch relationships not properly perceived increases our mental gymnastics and tires us, causing us to label the music as "boring." Said another way: the less the ear/brain works to create a live music illusion, including pitch perception, the more we enjoy it and the longer we want to listen.
We hope to post binaural recordings in the future with the intent to demonstrate SG performance, including Toole's conclusions regarding pitch perception.
Our tests indicate that other benefits include greater perception of detail, nuance, wood tone, fingering styles, and as stated earlier, all parameters relating to spatial qualities. Proximity effect is minimized, meaning the sound detaches from and is not localized in the vicinity of either cabinet. Image height is raised in the sound field, as even the pickiest reviewer Jason Victor Serinus mentioned in his comments Re. $5500/pr AK Zephrin 46 (2015 THE Show, Stereophile; on Robert E. Greene's list of “Best New Speakers Under $15k/pr”). Another interesting benefit may seem anti-intuitive: listeners perceive less of the listening room and more of the music program acoustic. And there's no known down side.
We call it "Space Generator" because listeners perceive it as enlarging the dimensions of their sound room. It may seem anti-intuitive, but proper magnitude of late-arriving, wide-dispersion, properly filtered energy portrays more of the program acoustic and less of the listening room acoustic signature.
What is an ideal method to minimize early-arriving reflected energy combined with a high ratio of ideal late-arriving reflected energy? The goals seem mutually exclusive because they are. Duke has invented a method for audiophiles to have their cake and eat it too.
First, if you're looking for an active speaker, this is not the place. Duke and I both value the benfits of employing the world's best external audio amplifiers, not the type usually employed in active speakers. (A passive crossover can also improve performance by modifying the impedance curve.)
Duke's main speakers all feature a tightly focused constant-directivity pattern for early arriving signal, with among the lowest magnitude of early arriving reflected energy. We agree with Dr. David Griesinger, who states that the less is early arriving reflected energy, the better is performance. (Not to get too deep in the woods, but this is one little sliver of daylight between Toole's philosophy and Griesinger's: Toole specifies that some degree of early arriving reflected energy benefits performance.)
AK's Space Generator is a discrete speaker with separate input and crossover. Duke has tailored SG response based on years of research and user feedback. SG has very high input impedance, 20 ohm to 50 ohm depending on the model and setting of its passive volume control. Most amplifiers can properly drive the front/main AK speaker and Space Generator in parallel (contact us for specific advice).
The SG has a passive wide range level control and 5 setting Treble Tilt control (see TT notes elsewhere herein). SG drivers comprise a compression driver with, depending on the model, either a coaxial cone or ultra-wide range horn.
How does the SG achieve or approximate the 10 ms delay target described earlier? The SG driver mounts to either a 22.5 degree or 45 degree baffle, firing the SG rearward and upward toward the ceiling. Even with the speaker moderately close to the front wall, SG energy is delayed about 10 ms relative to early-arriving signal.
We minimize SG's potential off-axis early-arriving energy with pattern control and by installing the driver in a rear-facing notch. "Release Holes" (AKA "Bubbles") on the inside vertical panel minimize early arriving reflected energy that would otherwise degrade performance.
If we compare sound patterns to light, think of the early arriving, constant-directivity signal as a focused light beam, followed about 10 ms later (11.25 feet path length difference) by a flood lamp with its spectrum modified for certain desirable attributes known to maximize performance. The results are pleasing and addictive. Scroll one section above for an in-depth description of the many benefits. And there's no downside when following our easy setup instructions.
Prior to 2018 even on the two critical series capacitor banks for the compression driver, Duke used the smallest number of caps needed to achieve the required value. Since 2018 he switched to higher cost capacitors, with a large number of lower value caps to achieve the required value. The result is faster transient performance, with increased detail, transparency, larger dynamic envelope, and no down side. He also switched to higher cost coils.
Some models may have different plating material on each polarity for a pair of input binding posts, e.g. gold plated positive post + rhodium plated negative post, or one gold plated/the other nickel plated. This non-symmetry splits the difference between the best and least desirable acoustic traits of each plating material, with concomittant performance upgrade.
Our CNC cabinet shop contributes to AK's high value. The shop charges less than the average rate for a high level of craftsmanship, which savings we pass along. The only down side is that lead times vary from 2 weeks up to 4 weeks, and occasionally (but rarely) longer.
Speaker cabinet construction is a fine art, with considerable learning curve for even accomplished cabinet craftsmen lacking such experience. Our CNC craftsman has built speaker cabinets since the mid-00s and has a fine grasp of the many related nuances. Multiple AK speakers assembled in the USA's driest climate in Utah, are trouble free even in the damp environs of Florida, Jakarta, and N. Carolina, among other places.
“Gold Ply” Panel Material, Pre-Veneered Both Sides
Except where noted, all panels comprise Gold Ply, AKA Gold Core or CLX, a unique panel material comprising birch + MDF, pre-veneered on both sides. MDF is strong, lacking grain, knots, and rings, resulting in clean, smooth rabbets to flush mount drivers. MDF also increases mass for stability and less cabinet rocking. Cross grain birch minimizes shrinkage and expansion, thus maximizing strength and consistency.
The two panel materials outperform either material alone. Noise is lowered, with commensurate increase in dynamic “pop,” and without any downside.
Both panel sides are pre-veneered under extreme pressure at the mill, further maximizing longevity and stability. The area around front drivers is double thick. Mass, window frame braces, and/or perimeter bracing is added as needed.
Paint and Veneer Finishes
Gold Ply comes in these 15 different veneers. Our CNC shop has a wide array of pleasing stains and finishes. Automotive finishes are available, which may increase cost.
- African mahogany
- Clear Alder
- Knotty alder
- Knotty pine
- Natural birch
- Red oak
- Vertical grain fir
- White oak
Knit Cloth Grille, Mid-Woofer Dress Ring
Knit Cloth Grilles w/Ball and Socket Fasteners: add $600/pr for all models except Gina, which includes standard Mid-Bass Dress Ring described below (no grille option for Gina, which would hide its proprietary poplar wave guide).
Alloy Satin Black Mid-Bass Dress Rings: included standard on Gina, add $250 per each pair of 10 inch mid-bass except Gina where the ring is included standard; add $350 per each pair of 12” mid-bass.
Dual Flared “Precision Ports”
All ported speakers employ Precision Ports with scientifically engineered flares on both ends to minimize turbulence.
Our first choice for port siting is directly behind the mid bass, to increase late- arriving mid range reverberant field energy. For models with ports behind the mid bass and and at other locations, when plugging ports to tune response, always plug ports behind the mid bass last.
Cherne Pipe Plugs
For bass tuning, all speakers with ports include a Cherne pipe plug to air tight seal each port. An air tight seal is superior to the typical practice of stuffing a sock in a port.
5 Position Treble Tilt Alters Curve and Gain
Compression drivers each have a “Treble Tilt” control. Each setting changes both curve and gain, for more effective control than one or the other. (Tannoy's $30k/pr Canterbury model has controls for mid-treble curve and gain.) A pair of rear panel non-polarized binding posts is labeled “Treble Tilt.” The 5 user choices are as described below:
- +2: included shorting jumper
- +1: included non-inductive power resistor labeled “+1”
- 0/flat: included non-inductive power resistor labeled “0/Flat”
- -1: included non-inductive power resistor labeled “-1”
- -2: posts open, nothing connected
In the rare case of a user preferring a half-step between the OEM whole steps, let us know the desired step location, e.g. +.5, -1.5, etc. We shall ship a pair of power resistors of the appropriate value, and labeled with your desired step number.
Footers, Gliders, and Spikes
Subs come with four 1” rubber feet. In 2018, for all floor standing speakers, we switched to four Peavey brand “glider” feet with additional rubber section for total height of .93 inch. For hard floors, each floor stander includes 5 (4 + 1 spare) self-adhesive felt gliders. Users fasten the felt gliders to the nickel glider base, and wait a few hours for the adhesive to cure.
Beyond maximizing ease of general placment, gliders allow the highest degree of siting accuracy. You'll love this quality of the gliders, and never want to go back.
Floor standing speakers also include a front/center mounted threaded insert, a spike, and padded cup. After siting speakers to the desired precision, Person A stands behind the speaker with their feet locked behind the two rear gliders, and gently tilts the speaker backward toward their body. Person B slides something solid (book, wood pieces) about 2 inches tall under the speaker front (to prevent spike injury), then screws all the spike thread into the insert, and removes the book or wood. Person A sets the speaker down. Set the spike past the carpet into a concrete or plywood sub floor below. In case of carpet above hard wood/composite floor, set the spike into the cup. In case of tile, linoleum, hard wood or composite floor, put the pad under the cup and set the spike into the cup.
Stand mount speakers come with feat comprising 1 inch diameter circles of appropriate thickness, cut from panels of Sorbothane or 3M ISODAMP (the latter is used to damp magnets in MRI machines). Circles fasten with included “3M Removable Mounting Putty Cat 860.”
A client/tracking studio owner gave us a formula to select feat based on a damping material's “duro” number and the speaker or component's weight. Circle shaped feet are ideal because circles compress linear throughout their area, while a square compresses most in the center and least near the edge (uneven wear).
For clients desiring feet for products purchased elsewhere, we happily cut custom circular damping feet to the proper spec per application, using Sorbothane or 3M ISODAMP, for a little over our material cost.
Price Includes Padded Shipping Crate or Carton
Non-transferable 5 year warranty on materials and workmanship. Buyer is responsible for all shipping.
US and International Shipping
FOB Providence, Utah. For US clients we get 40% FX discount. DEBRA sub cabinets about $40/ea to CA, highest we've seen is $65/ea to New Jersey. For international clients Concordia's air freight fee is the absolutely lowest known and their service is impeccable.
Specifications Subject To Change
Your standard disclaimer in the case of performance oriented changes!