DEBRA Distributed Enhanced Bass Reflex Array

DEBRA is an AudioKinesis licensed clone of AK Swarm.  DEBRA cabinets are wider and shallower, comprise a different panel material and all subs have one pair of inputs.

New!  Foolproof, Simplified, “Progressive Null Point” Setup Instructions

No comparable commercial system, a unique solution from nature: the room’s pre-existing fixed modes + four subs at “Progressive Null Points” = flat response and the smoothest, most musical and natural bass throughout the listening room. “Room Gain Complementary” tuning (Duke LeJeune) inverts the boundary curve <100 Hz. Unsurpassed pitch definition with the “elastic” qualities of bass in a commercial space.

No after-the-fact band-aid as per every other bass mode “cure”. No “hot spots.”  No automated EQ. No acoustic treatment. No proximity effect.

Studio or home. A new state-of-the-art reference for music. Conservatively rated 113 dB @ 20 Hz for knockout HT punch.

• Four reflex subwoofers (each with Cherne pipe plug to convert to sealed) + one Dayton Audio SA1000 kilowatt bass amp/EQ: 950W @ 4 ohm (1/3rd duty cycle), continuously variable low-pass crossover, panel or rack-mount, single-band parametric EQ
• All orders custom, ship within 30 calendar days
• Frequency Response: flat 18 – 80 Hz with single included SA1000, 150 Hz crossover requires 2nd SA1000
• Total System Weight: subs 39.5#/ea x 4 = 158# total (sub amp drop ships free)
• Four high output 10.5″ subwoofer drivers, power handling 600Wrms/ea x 4 = 2400Wrms system, black anodized aluminum cone, vented triple shorting ring motor increases reliability especially under abuse, normally reserved for only the most costly high-end drivers
• Voltage Sensitivity: total system 91.5 dB
• 1 spike, cup and damping pad, centered under the driver
• Unique qualities of bass reproduced in a commercial (large) space
• Each sub 39.5#, H x W x D 23″ (+1" feet) x 13.5″ x 10.75"
• Conservatively rated by designer Duke LeJeune for 113 dB clean output @ 20 Hz
• “Room Gain Complementary” tuning (Duke LeJeune) + natural acoustic mode-canceling effect without EQ/absorption/resonators for the flattest, most natural bass throughout the listening room (buildup only in extreme corners)

Three Cabinets Too Many?

In reply to your thought, “DEBRA has about three cabinets too many,” DEBRA subwoofers:

• Comprise a classic design occupying only 1cf, finished in a choice of 15 different veneers
• Distribute easily throughout the room, against the walls, in enclosures only 10.5″ deep…only four visible panels per subwoofer, drivers face the walls
• Offer a unique combination of performance and features available nowhere else

Introduction

Dr. Robert E. Greene is Senior Editor at The Absolute Sound Magazine and Math Professor at UCLA. He also tutored Russell Crowe in the violin for “Master and Commander” and Russell’s Appalachian accent for “A Beautiful Mind.”  In TAS Issue 252, April 2015 (and 2 subsequent issues) Dr. Greene reviewed AudioKinesis Swarm Subwoofer Array and awarded it his Editor's Choice Award three time, AK's second, third and fourth major journalism awards.  DEBRA is similar to Swarm, with different cabinet materials and dimensions (wider and less deep).

DEBRA is the result of my personal search for affordable, state of the art bass in two successive sound rooms with horrific bass mode problems.  In the first room I spent $750 for professional plans and several thousand dollars on professional acoustic treatments including a three-walled acoustic soffit with at best, mixed results.

Hearing is believing. The worse the room’s bass modes, the greater is the array's performance advantage. DEBRA produces bass with the “elastic” and musical qualities of bass in a commercial (large) space. Consider DEBRA your “last purchase” subwoofer for any music system or home theater system.

DEBRA employs four subwoofers each with a high-output reflex-loaded 10″ driver. Duke LeJeune of AudioKinesis specified the drivers, distributed array concept, and special “Room Gain Complementary” tuning. We specified original “Progressive Null Point” siting instructions, special panel material, and a slightly wider and shallower cabinet.

Two Rooms In One

By late 2008 I was convinced a properly designed Distributed Bass Array defines state of art bass reproduction in any domestic space. Conversely, regardless of cost or complexity, full-range single-column speakers are inherently flawed by design, their performance depending on almost endless variables all or most beyond the user’s control.

The bass array excels because a domestic room (a small space, as compared to a commercial size room such as a theater) affects sound waves differently above 150 Hz vs. below 150 Hz. We admit the audiophile “heresy” in the following statement: a domestic music system achieves the smoothest, most seamless, most coherent, and most musical bass with a subwoofer system separate from the mid/treble system.

Domestic rooms have “modes” related to room dimensions causing serious time and frequency distortion in the bass range. Bass modes cause many audiophiles to prefer smaller speakers with less bass power and higher bass cutoff.

Professional reviewers often describe a laborious, time-consuming process of siting speakers for ideal, smoothest bass performance, then readjusting again for preferred mid/treble performance. The process repeats, presumably till attaining the best sonic compromise. The deeper and stronger the bass, the greater the modal effects and the longer and less-successful is the juggling process.

In October 2011 Jeff Hedback (Hd Acoustics) and Nyal Mellor (Acoustic Frontiers LLC) published Acoustical Measurement Standards For Stereo Listening Rooms. Hd Acoustics clients include Ozzy Osbourne, Lifehouse, and Trevor Horn. Page 19:

To obtain the best possible LF response…boundary interference issues can be tougher to address. Varying the fixed distances from ‘speaker to boundary’ and ‘listener to boundary’ will reduce strong cancellations. It is a balancing act as one location that may offer a smoother LF response may not provide the optimal midrange and treble response.

Page 20, paragraph 2:

everyone desires a ‘flat’ LF response and no modal ringing. Simply, this is a tough achievement. The absurdly large collection of interrelated variables between two full range speakers and the room (speaker design, speaker/listener location, room size/construction and acoustical control within) makes this so. It is up to the individual to determine what their limits are as regards placement and acoustical treatments

Note the troubling and painfully accurate descriptor:

absurdly large...variables

Note: I am solely responsible for the following conclusion. To my knowledge no one including Mr.’s Hedback and Mellor endorse the following conclusion. Toward the goal of ideal sound reproduction in a domestic space, the above quotes demonstrate that full-range loudspeaker architecture contradicts the mutually exclusive requirements of bass vs. mid/treble siting. Ideal performance in any domestic space requires separate locations for bass speakers and mid/treble speakers. Google “Schroeder Frequency” for further information explaining how domestic spaces react differently in the bass range vs. the mid/treble.

Listen carefully to music in a theater.  Notice the “elastic” quality of the bass, perfectly integrating as one seamless whole with the mid and treble range, never drawing attention to itself and never being differentiated from the mid/treble. Commercial spaces have modal effects but the boundary dimensions and resulting wavelengths are so large that the modal frequencies are below the audio range.

Conversely, full-range bass in a domestic space often sounds disjointed from the mid/treble, as if the bass is in a different dimension. Over time, once familiar with the performance excellence offered only with a Distributed Array, you will likely notice a strange a-musical quality associated with even the very best full-range loudspeakers in a typical domestic space: bass seems to hover in proximity to the loudspeakers, more so with certain bass notes than with others. The listening room boundaries never fully disappear. Conversely, Distributed Array bass integrates perfectly and consistently into the sound stage with the rest of the performers. The listening room walls disappear to portray the program sound stage, varying dramatically between programs.  With bass flat to 20 Hz throughout the room, live bass cues abound, including the effect of feeling like one needs to swallow to equalize their head with deep bass pressure changes, or the feeling one associates with plunging down the steep slope of a roller coaster.  Pressure changes are natural, visceral and unexaggerated.

After careful consideration you might agree the phenomena described above is the biggest difference between live music in a concert hall and reproduced sound in a domestic space. (Dynamic compression and reflected-vs.-direct energy are not-too-distant seconds.)

Remember the above is only a broad comparison of domestic rooms vs. commercial sound reinforcement systems. DEBRA goes at least 1 octave lower and surpasses all performance specifications (except SPL) of any sound reinforcement system.

Once you become familiar with DEBRA’s performance advantage the weakness of any full-range speaker, regardless of cost or complexity, stands in stark relief.

All known setup comment for single-column speakers with true 20 Hz output discloses (usually indirectly) the flaw inherent in such design: ideal location for bass is mutually exclusive of mid/treble requirements. This is an audiophile secret, the skeleton in our closet, the pink elephant in our media room implied but never confronted because of inherent flaws in prior solutions.

The Distributed Bass Array is a new high-end audio standard for bass reproduction in a domestic space. We believe the Distributed Array eventually displaces all full-range architecture as a high-end reference.

Alleged Modal “Cures”

Purpose-built commercial and domestic sound rooms have Golden Ratio relationships to minimize audibility of bass modes. After-market so-called “cures” for bass modes include:

Helmholtz resonators
Acoustic absorbent such as fiberglass
The ubiquitous digital electronic room equalization (“EQ”)

Resonators are too large and require a separate box for each band of frequencies. Fiberglass absorbent is costly, takes almost endless quantities to absorb deep bass waves, and cause bass to sound overly dry (one popular maker/seller of absorbent room treatment simply instructs shoppers to purchase as much fiberglass as they can afford, meaning “more is better”). Absorbent and Helmholtz resonators are unattractive and take up far more space than DEBRA. EQ causes multiple severe “hot spots.” It is difficult to impossible to boost the worst response dips with any of the above band-aid fixes.

The audio industry markets EQ as a panacea and most audiophiles perceive it as such. EQ is an elixir for audio marketers because it’s small, affordable, and reviewers and manufacturers publish attractive graphs displaying flat frequency response. Audiophiles believe in it because audiophiles are people and people are eternal optimists for the proverbial “free lunch.”

The problem with EQ is that it flattens frequency response in a static one-dimensional state, but modes exist in three dimensional space. EQ provides absolutely no relief for the worst modal effect, which is timing distortion. Timing distortion is perceived as bass notes ringing after the bass player or bass section already hit the next note.

Flattening FR in one location worsens response the same amount (or more) in other locations. For a maximum of one listener whose head is locked in place, EQ has some theoretical potential, but even then, depending on the severity of a dip, it may require thousands of amplifier watts and commensurate speaker power handling, at incredible cost.

It’s more common now for digital EQ to sample and average the response at multiple room locations. This is hardly an “improvement” over one room location because it simply trades the advantage of one spot for less flat response at multiple locations.

The bottom line with EQ is it remains a zero sum game: rather than curing, solving, or eliminating the fixed mechanical problem of the room’s modes, even infinite EQ (impossible because of power constraints) can only “improve” the response at one location the same degree it detracts from performance at another location and/or locations.

Check this last item if you reply, “Me thinks thou dos’t protest too much about EQ…:” Beyond EQ being a zero sum gain throughout the room (regarding FR), EQ does nothing to ameliorate the more audible problem of ringing/time smear. Bass notes associated with modal peaks continue to “ring” in the room after the bass player stopped and hit the next note.

Bass modes result from the room’s fixed, physical dimensions. It’s ideal to stop them from propagating in the first place rather than fix them after the fact.

BLAZING A NEW TRAIL

Duke LeJeune of AudioKinesis, Dr. Earl Geddes, Dr. Floyd Toole, and Todd Welti blazed a different trail. In a nutshell, they specify three or four subs distributed throughout the room. Properly tuned and sited (my original instructions below), the subs act as new modes unequal to the room’s natural fixed modes. We reverse the polarity of one sub relative to the others to increase the unequal mode and smoothing effect (reversing polarity of two subs diminishes first octave power).

This bass philosophy promises all good things. The only risk is financial (admittedly, subs of this quality can not be built on-the-cheap). The reward is the best bass you’ve ever heard, everywhere in your room, including the corners.

“Equalized” frequency response (FR) in the bass range throughout the room is impossible. EQ makes FR more erratic everywhere except the mic calibration site. Audiophiles generally desire a larger so-called listening “sweet spot,” yet EQ decreases the sweet spot to a sweet “dot.” Turn your head a few degrees and response may be worse after EQ. Let us know if you ever see a professional review publish response graphs outside the mic calibration site(s) before and after EQ is applied (we won’t hold our breath waiting for such to appear).

For the entirety of a domestic room bass modes cannot be electronically “equalized.” Rooms are not air-tight, but we can still compare the room to a pressurized balloon. Pushing in the balloon at one spot deforms the balloon at another location. The pressure stays almost constant throughout the balloon. What EQ “fixes” at one spot in the room it makes worse at other spots.

Architecture vs. Quantity

I estimate well over 1000 published pages debating the relative merits and demerits of sealed, bandpass, bipole, dipole, ported, field coil, spaced dipole, corner-loaded, open baffle, and passive radiator systems for state-of-the-art bass reproduction. Add or delete servo-feedback control to any of the forgoing. Then there’s still planar, ribbon and electrostatic architecture (push-pull or single-ended for the first two).  Want more? In the mid-2000’s Eminent Technology released an electric-motor fan (rotary) subwoofer that requires an amp capable of driving 1 Hz! A vocal proponent of one particular architecture might have several letters of science after his name with an argument supported by graphs, diagrams, and formulas. Very convincing indeed.

Thankfully, and what a relief, Dr. Earl Geddes put this debate to bed by thoroughly documenting that regardless of bass system architecture, a bass waveform reflects between two boundaries before one complete cycle is audible. In sequence, first the boundary makes its indelible imprint on the bass waveform, then listeners perceive the waveform. For this reason and in this way, the boundary effects are more significant than differences between various sub architectures (presuming the subs are appropriately tuned).

Dr. Geddes proved the sub architecture is less critical than a minimum quantity of three subs, necessary to minimize the above described impact of the room’s boundaries. (Distributed Sub Arrays have one special tuning requirement unique to their architecture.)

Bass Quality Myths

Let’s suppose we are concerned only with well-built and properly tuned bass systems of all types (sealed, reflex, etc.), wired properly and driven by an amp with power reserve and adequate damping factor. Listeners often wrongly correlate perceived bass qualities such as “quick,” “slow,” or “boomy" to woofer size, system type, tuning specifications, or combinations thereof.

In reality such perceptions result from geographic relationships between the two speakers, the listener, and the room’s boundaries. For instance, perception could change from "lean" to “boomy and muddy” by changing the music program and/or the position of the speakers, the listener or both.

Ancillary Benefits

Separating a system into two component parts provides several other noteworthy benefits. The bass range has its own dedicated amplifier and likewise the mid/treble range.

Large, heavy, sub drivers capable of solid 20 Hz output require maximum current and voltage at long wavelengths, very different from qualities associated with state of the art mid/treble. Bass amp requirements lend themselves to lighter, smaller, lower cost, cooler-running, highest efficiency Class D architecture. Conversely, the mid/treble amplifier requires maximum resolution of shorter wavelengths, without concern for bass performance.

The number of speakers with limited bass output is much larger than speakers flat to 20 Hz. Stand-mount monitors minimize cost and space, integrate easier into a living space, and often offer better spatial performance.  Floor-standing speakers have larger panels more prone to resonate. 20-Hz drivers sharing the same enclosure with mid/treble drivers requires Herculean mass and damping otherwise unnecessary with separate subs (some preferred single-column speakers weigh over 400 lbs each…take a look at the incredible, intricate super structure comprising Magico’s largest floor standing loudspeaker).

Single-column speakers capable of 20 Hz require large enclosures. The larger the internal enclosure dimension the lower the resonant frequency of each panel, and the more likely is it to resonate within the woofer bandpass. It’s possible to work around these problems…and always costly. And still, regardless of architecture, engineering and ultimate cost, no single-column speaker has DEBRA’s wide-bandwidth mode cancelling effect. (Costly, huge, floor-to-ceiling towers filled with multiple woofers cancel the dominant ceiling mode. But DEBRA mechanically equalizes all modes including the ceiling, for lower cost and with less environmental impact.)

DEBRA’s setup process takes less time and effort than the never-ending trial and error associated with full-range speaker siting. Professional reviewers sometimes modify speaker setup even after the speaker’s designer spent hours at the same task.

Also, DEBRA allows for mutually exclusive ideal siting of the subs and main speakers, something impossible with all single-column full-range speakers.

Every difference between DEBRA and even the most complex cost-no-object full-range single-column speaker favors the former over the latter.

Why Not 20 Hz? Lower than 20Hz?

For listeners whose goal is highest performance, we wonder why anyone should settle for less than 20 Hz performance when considering a state of the art reproduction system. Further, we wonder why someone would consider something state of the art that does not employ a technique nature offers (dilution of the room’s bass modes) as the first choice to solve vexing bass mode issues.

Some fanatics may desire a cutoff below 20 Hz, and we sympathize with lofty performance goals. But keep the following in mind. For sealed systems driver excursion squares for each lower octave. For reflex systems such as DEBRA, driver excursion is maximally damped at the port tuning frequency. The lower the bass cutoff the lower is port tuning and the lower is the frequency at which the driver is damped.

Compare a system tuned for an f3 of 16 Hz vs. 20 Hz: the 16 Hz system of course makes power 2/5ths octave lower than the 20 Hz system (for the rare recording with 16 Hz present and rare system capable of reproducing it). But at higher mid-bass frequencies driver excursion is lower in the 20 Hz and greater in the 16 Hz system. For all music program, there is much more mid-bass content than that at 16 Hz. In the mid bass the 20 Hz system distorts less and has greater power handling than the 16 Hz system. The human ear may not be sensitive to the difference in distortion, but the 20 Hz system has a larger and safer power envelope than the 16 Hz system at higher, more common mid bass frequencies.

How many 16 Hz pipe organ and synthesizer recordings do you have?

Home Theater Performance

We have a unique dual use system for both music reproduction and home theater. For video there is a 1080P front projector and 92″ retractable perforated screen about 7′ from the front wall. DEBRA provides sub duty for both music and HT. This audio system provides previously unheard HT performance, especially spatial qualities (imaging, stage depth, sound intensity, etc.).

Over four years of use reproducing every HT audio effect in the bass range, I’ve reached for the volume control to save my ears and maintain some semblance of domestic tranquility, but never exceeded the bass system’s output capacity.

“Room Gain Complementary” (RGC, Duke LeJeune) Tuning

Duke LeJeune of AudioKinesis coined the term Room Gain Complementary (RGC) tuning, described HERE. Duke’s “Dream Maker” bipolar speaker won The Absolute Sound’s 2008 Golden Ear Award. Duke also designed and manufactures what independent musicians agree is the best compact speaker cabinet for electric bass and all acoustic instruments, the AudioKinesis Thunderchild (see the 51+ page AudioKinesis 112 thread w/ 1000 posts + Part Two ).

Duke added excellent gilding to the multiple subwoofer lily. Beyond modal effects, domestic rooms boost the bass an average of +3 dB per octave below 100 Hz (+7 dB @ 20 Hz). Comparing sealed tuning vs. standard reflex tuning, the former more closely mimics Duke’s RGC tuning than the latter. We believe this is the most common reason why some audiophiles prefer sealed systems over reflex, not the difference in transient performance nor phase anomalies. (A less common reason for preferring sealed systems is that modal peaks sometimes match a ported speaker’s tuning frequency, resulting in grotesque one-note bass. Again, for all properly tuned bass systems, the enclosure type is irrelevant compared to the minimum quantity of four subs.)

Stereophile Magazine well describes this effect in their 2009 review of Harbeth’s superb 40.1 monitor. It’s flat anechoic deep bass response is better suited for larger rooms, whose modal effects are lower in frequency than smaller rooms. (I loved the Harbeth 40.1 at 2008 T.H.E. Show.)

No Proximity Effect

Debra bass is so non-localized (no proximity effect) that DEBRA subs are completely invisible as a sound source. You’ll have to touch the driver or the enclosure to confirm it is active.

Blending With Different Main Speakers

DEBRA ideally blends with any main speaker regardless of architecture, whether bipole, dipole, monopole, or omnipole. Prior to Distributed Bass Array audiophiles associated bass performance quality to the architecture and/or construction quality of various sub woofers sampled over the years. Distributed Array proves these performance qualities are predetermined by bass mode effects. DEBRA is more adaptable and easier to blend with any possible main speaker preference. DEBRA performance equals or exceeds any future changes in your room, main speaker quality and/or radiation pattern. Once you correctly conquer the bass mode conundrum you can happily spend your audiophile days sampling any and every speaker technology above 80 Hz. The whole question, “Is my sub ‘fast’ enough for _____ main speaker?” is moot.

Summary

To summarize, the room’s modes cause irregular bass response. In effect, each of the multiple subs dilute the room’s modes, resulting in flatter response at all points in the room.

DEBRA’s small subs and the ease with which they integrate into a domestic space make DEBRA the ideal bass solution.

Herculean power, RGC tuning, and natural mode-flattening effects leave nothing to be desired in state of the art subwoofer performance.

Walk around a room employing standard sub technology or single-column speakers with deep, powerful bass. Whether or not EQ is employed, the modes in domestic rooms result in big response swings at different locations. In spite of my room’s otherwise horrific bass modes, DEBRA sounds linear and natural throughout the room, even in all four extreme corners.

Comparing One Sub vs. Four

My regular demonstration technique is to play a good jazz acoustic bass at moderate level. I disconnect three subs, leaving only one sub playing (this sub is sited where it produces the smoothest bass). I increase sub amp gain 4.5 dB (would be 6 dB except that one sub polarity is inverted). Listeners immediately notice:

The double bass looses about half its sound quality
The sound stage collapses and intensity decreases…instead of the music energizing the entire room it is focused only in the front Bass FR is rougher and some notes disappear…transient leading edges are dulled…the musician omits certain notes and follows the beat with less accuracy.

See the table near the top of this page. 100 Hz to 20 Hz, swept sine wave, 60 dB @ 63 Hz, mic @ sweet spot, no EQ: one sub in the smoothest location plays within a 13 dB window plus much larger nulls and peaks throughout the room, especially in corners. DEBRA (four subs, one phase-inverted) plays within a 6 dB window throughout most of the room including all four corners. The difference is hugely audible and anything but subtle. The above notes hide DEBRA’s true advantage, which is proper bass note time values. Standard bass systems cause notes to ring long after they stop on the program material, even after a new bass note of different pitch occurs, resulting in two disharmonious notes. Once you hear the absence of this defect you can’t go back.

Enclosure

Please see "Enclosure Details" link under "AK Speaker Design."

DEBRA Progressive Null Point Setup Instructions, copyright James Romeyn

Contact us for easy in-wall setup instructions.

Read all setup instructions before starting.

Insure cone supports stay clear of all wire and cable.

A small black arrow on the top panel center (close to the baffle) denotes the reference point for siting subs.

All four subs site with the driver baffle about 1-3/8″ from a wall, for a clean uncluttered appearance.

Screw a threaded stud into each speaker support cone. Screw three speaker support cones into each sub.

Siting Four Subs

Our first goal is to confirm the first null point (near a wall) with the smoothest, most linear bass for the first sub. This test mimics or “mirrors” the boundary, subwoofer, and listening seat relationships during normal listening.

If the floor is finished wood (even if carpeted over), use the included flat discs under flat speaker cones. If there is carpet over concrete or unfinished sub-floor, screw the points into the speaker support cones and use no flat discs.

Measure and note your ear height in your favorite listening seat. Set the sub amp crossover pole to 80 Hz, flat parametric EQ, and phase control to 90 degrees (control @ 12:00, vertical).

Clear all space including furnishings about 2-3′ from all walls or from as much of the walls as possible. Clear the space normally occupied by the main listening seat. Under the primary listening site (“sweet spot”), center one sub face-down, woofer firing up toward the ceiling. Connect this “sweet spot sub” to the amp.

Play well recorded music program with electric or upright bass, preferably with brief note values over a one-two minute period or longer. Kneel or bend at waist to locate your ears about 2-4″ from the wall, equal to ear height in the listening seat. Alternately employ SPL meter. Listen (or place SPL meter) at all points 2-4″ from wall surfaces, for the smoothest, most linear bass, with the least ringing and lowest overall gain. Attach a “Post-It” note to walls at one to three sites most closely matching the qualities described above. Re-test at “Post-It” note sites to select one site with the best performance. Take your time with this process. Double-check results.

Site “sub 1” on its cones for normal use, near the wall at the final location with the best performance. Connect the sub amp to the “sweet spot sub” and “sub 1” in series (8 Ohms total), .

Play the “sweet spot sub” and “sub 1”. Repeat the above procedure, selecting two to three preferred locations, then narrowing it down to one ideal location. Locate “sub 2” at this point. Connect the amp to the “sweet spot sub,” “sub 1,” and “sub 2” in series (12 Ohms total).
Play the “sweet spot sub”, “sub 1,” and “sub 2”. Repeat the above procedure, selecting two to three preferred locations, then narrowing it down to one ideal location. Locate “sub 3” at this point. Follow text on terminal boards, connecting the amp to the “sweet spot sub,” “sub 1,” “sub 2,” and “sub 3” in series/parallel (4 Ohms total). Select two to three preferred locations, then narrow it down to one ideal location. Move the “sweet spot sub” to this final ideal location.
The four subs are best sited to act as four new random modes, unequal to the room’s fixed modes, thereby maximizing potential for the smoothest and most linear bass throughout the entire space of the listening room.

Sub Amp Phase Control

Set this rotary control knob at 12:00 (90-degree phase) for maximum expansion of the sound room’s boundaries, thus minimizing modal effects. The final stage, inverting the polarity of one sub, further minimizes modal effects.

Invert Polarity of One Sub

A tripod-mounted SPL meter at ear level at the sweet spot, and swept sine waves below 100 Hz (100 Hz, 80 Hz, 63 Hz, 50 Hz, 40 Hz, 31.5 Hz, 25 Hz, 20 Hz) greatly aids this process. Lacking such, we recommend, as before, employing well recorded jazz upright bass playing a long section of fast notes of equal time value.

Inverting the correct sub produces the smoothest, most linear bass, with the least ringing and lowest overall gain.

The only subs employed to invert polarity are the two 4-post subs. Invert a 2-post sub by inverting only the nickel (“SUB”) binding posts under its interconnected 4-post sub. To invert a 4-post sub, invert its nickel “SUB” posts and its gold ”AMP” posts.

If necessary and if employing SPL meter, wear noise protection for this process. Play above-specified swept sine waves four times, noting SPL each time, each time inverting the polarity of a different sub. You will easily note smoother performance with one particular sub inverted vs. the others.

Wiring

Insure cone supports stay clear of all wire and cable.

The sum total (100%) of the resistance of a speaker circuit = the series speaker wire resistance + the driver(s) resistance. The higher the driver resistance the lower is the speaker wire’s portion of 100% and the less does wire affect/impact performance. Other variables exist, but as the resistance of a speaker circuit goes up or down so follows speaker wire performance, justifying the following series/parallel wiring scheme.

On each 4-post sub connect its nickel (“SUB”) posts to a 2-post sub and connect its gold (“AMP”) posts to one of the sub amp’s two pairs of output binding posts.

Follow correct polarity throughout except for the inverting process described elsewhere.

Measure the wire length from the sub amp to the 2-post sub flanking the L, then from the sub amp to the 2-post sub flanking the R (disregard the 4-post sub for this measurement). To calculate minimum AWG, input the wire length at this site: https://www.bcae1.com/images/swfs/speakerwireselectorassistant.swf . The sub amp makes 1kW total into 4 subs or 500W into 2 subs. Type “500” in the calculator cell for wattage.

Overall Results

DEBRA, with unique cabinet build, employs exceptional overall design and engineering throughout.

My sound room’s bass modes are so strong that a single sub with EQ can not successfully integrate; results were similarly unacceptable with two small subs under each L/R monitor after pivoting the four subs in every possible combination of directions. Three subs properly distributed throughout the room (one must be sited above ear level) was only marginally successful.

The overall presentation with this system’s unique features is remarkable by any standard. Response is smooth and linear with an “elastic” quality and musically natural integration similar to a commercial (large) space.

DEBRA’s mono bass signal has no audible disadvantage compared to stereo. In the range of bass fundamental tones, stereo bass is irrelevant, even more so compared to well documented modal effects (severe ringing/timing distortion, +/- 10 dB is not unheard of). Consider the following relationships: the room’s boundary dimensions, bass fundamental wavelengths, and the distance between two stereo full range loudspeakers. How likely is a listener to discern disparate L/R signals in the range of bass fundamental tones, presuming one has a recording with such tones?

DEBRA provides low distortion, uncanny pitch definition, 113 dB @ 20 Hz (conservative), and smooth, musical response throughout the room. Over the past thirty years or so I have carefully auditioned the best cost no object systems from stereo electrostatic to Kimber Iso-Mic 4-channel to Andrew Jones’ TAD 5-channel Reference One (the later two systems with proprietary master recording sources).

We believe DEBRA provides a new state of the art reference that will spoil you vs. inferior sub systems. It’s not inexpensive, but on the other hand you could spend a lot more for yesterday’s architecture, less musical performance, and far less flexibility.

Dayton SA1000 Sub Amp

30.8 lbs

Rear panel:

All audio inputs RCA unbalanced: L/R are summed mono, use both or either. One “LFE Direct” input bypasses sub amp internal crossover.

3-position rear panel slide switch for power: Trigger/Auto/On

Front panel power switch.

DEBRA recommended default settings for front panel continuous rotary controls:

Parametric EQ, unused, set flat: “FREQUENCY” fully clockwise. “CUE” fully clockwise, “GAIN” 0 dB.

Phase: 90 degrees, 12:00, vertical

Freq: (crossover) depends on main speaker bass cutoff and power. Several benefits accrue with active high-pass crossover on the main speakers. We employ the active high-pass crossover in a Trinaural Processor (in-phase 2nd-order @ 80 Hz). DEBRA may cross up to 100 Hz.

Gain: as needed

Name Brand Competition

JL Audio’s Gotham g213 is certainly among the best name brand sub systems. It’s static specifications and premium build and finish quality properly reflect its stratopheric $12k cost.

Audiophiles sometimes prefer sealed bass systems like Gotham because they have no port. When a port tuning frequency happens to overlap one of the room’s many bass modes (frequently the case) the result is extreme bloat and overhang. Also, a sealed system’s slower roll-off rate mimics the effect of DEBRA’s RGC tuning. Finally, sealed systems generally have more linear transient performance.

But DEBRA has every advantage over a sealed system, even one as princely as Gotham. Reflex systems require multiples less power and cone travel (displacement) for similar power at the lowest frequencies (the cone of a reflex system is maximally damped/almost stationary at the port tuning frequency). The human ear has extremely low sensitivity to a reflex system’s transient distortion: harmonic distortion up to about 30% in the bass range is almost inaudible to humans, consistent with Dr. Earl Geddes’ conclusion re. architecture vs. quantity described elsewhere on this page. The tolerance for bass distortion does not extend to modal effects, which cause grotesque FR swings and distort timing, notes ringing long after they should have stopped. Note: maximum sensitivity to phase and harmonic distortion is in the mid-range, enabling a blindfolded person to accurately picture the arc of a coin turning on its edge, or the location and trajectory of a nearby predator.

DEBRA fulfills the loftiest audiophile goals for “quality” of bass reproduction at every physical location in any domestic listening space. DEBRA meets the classic 20 Hz cutoff goal and has acoustic power for HT applications.

Every fine, lasting, enviable structure starts with the strongest possible foundation. Every band and orchestra plays no better and no faster than its foundation, the bass. DEBRA is a fine, permanent foundation on which to build a lifetime of audiophile dreams. It cost more than the average sub system, yet compares admirably to products costing many multiples greater.

DEBRA offers original thinking and an ideal, novel approach to deliver state of the art bass for both music and home theater in a compact, attractive, affordable, and easily placed package.

Happy listening!