January 2025

PureAudioProject Duet 15 Loudspeaker Review
A benchmark performance open baffle loudspeaker.
Review By Dr. Jules Coleman

 Featuring the extraordinary Voxativ Pife full range driver mated to a comparably fast 15" woofer, the PureAudioProject (PAP) Duet 15 offers the listener an unrivaled, relaxed, unhurried, yet fully resolved natural and immediate musical experience that box speakers, for the most part, can only dream of providing, and one that competitor open baffle designs will struggle, most likely with only limited success, to equal. These speakers are unassuming, seductive, and enthralling. I found myself unable to resist falling into the music's awaiting arms for the better part of the several months I was fortunate enough to have them in my home.

What Is An Open Baffle Loudspeaker?
The term 'open baffle' is vague. The standard design consists of a single baffle (think of the 'front baffle' of an enclosed speaker) on which one or more drivers are affixed. All open baffle speakers produced by PureAudioProject are of this sort.

Though not normally a feature of them, there is nothing in principle that precludes an open baffle speaker from including side panels of various dimensions and shapes. Some of the very best-sounding open baffle speakers I have heard (and owned) feature partial rear panels in addition to elaborately configured side panels. Prominent among these are speakers designed by Keith Aschenbrenner of Auditorium 23, several of whose speakers have received glowing reviews in the French audio press. Many audiophiles will be familiar with his SoloVox, the only one of his designs to have been widely distributed in North America, which I have owned on two separate occasions and have reviewed quite favorably.

While most open baffle speakers feature conventional drivers, it is worth noting that PureAudioProject currently offers a speaker featuring a Heil air motion tweeter, and other designs featuring a front-loaded horn or a coaxial driver in place of either the standard or Pife version of the Voxativ full-range driver.

Different 'enclosures' create distinct challenges for conventional woofers as well as for full-range drivers, horns, and co-axial designs. A full-range driver, for example, the Voxativ, PHY, or Lowther, designed primarily to be implemented in a back-loaded horn speaker will react very differently when implemented in an open baffle design. This fact was a driving factor in the A23 modifications of the PHY drivers that he employed in his open baffle designs.

For reasons that I will touch on below, the PureAudioProject Duet's successful deployment of the OB-A15-SEN woofers which more often find their way into commercial, rather than home audio settings, is based on modifications of the woofers designed to eliminate the cancelling effects that dipole speakers would otherwise be expected to produce.

There has been a recent resurgence of interest in open baffle speakers, and many more designers have begun treading on the landscape and altering its shape and topology. Newer designs feature more eye-catching (and some might say aesthetically challenging) baffle configurations while others have favored baffles constructed of unusual materials. Typically, these materials are heavy and dense, making the speakers much more cumbersome than the norm for open baffle designs, a choice made, no doubt, to reduce or eliminate amusical resonances and vibrations, thus taking a page from what has become a more familiar approach to damping among several box-speaker manufacturers.

Time will tell whether these experiments bear fruit. I am particularly interested in seeing how those designs that rely on exotic or dense materials fare both sonically and in the marketplace. After all, one of the great virtues of the typical open baffle design is that it is relatively light and easy to move about while taking up very little space in one's room. Second, while audiophiles appear not to agree on much, nearly everyone longs for a speaker that 'disappears.' Some of these designs make the disappearing act quite challenging.

Why A Resurgence In Open Baffle Designs
Different speaker designs present music differently. This banality is not trivial. While every speaker designer aims to provide a musically persuasive and satisfying rendering of the source material, there is no denying that different design types do so in characteristically different ways. The choice to produce an enclosed speaker, an electrostatic or a horn, an open baffle, or a planar magnetic loudspeaker likely reflects cost, manufacturing, and other factors. It can also reflect a designer's 'musical point of view.'

I don't mean to suggest that every designer has a well-developed musical point of view, that is, a conception of what is important to convey for a listening experience to achieve what the designer thinks it should: for it to bring forward the musically significant features of the recording including, but not limited to, its emotional and narrative or cognitive content, as well as the author's intentions and the interactions among the performers.

My view is that the most significant audio components are those whose designs and execution are driven more by an aesthetic vision than by manufacturing or other forms of technical acumen.

For designers who have a developed musical point of view, the choice among speaker categories is thoughtful and intentional. That makes reviewing their products particularly enjoyable and educational for me. For it is their musical point of view as well as the extent to which they can realize their vision that drives them and interests me. Every familiar speaker type has desirable characteristics – from a particular musical point of view – as well as those that present challenges to realizing their vision in practice. Unsurprisingly a conventional 'wisdom' appears to have developed regarding both the virtues and vices associated with each speaker type.

For example, conventional wisdom has it that because planars, electrostatics, and open baffle designs lack enclosures they cannot fully pressurize the drivers and thus lack ultimate dynamics and are limited in their capacity to play at significant volumes that some music calls for. On the other hand, horns and enclosed boxes are commonly criticized for their 'honking' and box colorations, respectively.

And so on.

When trying to explain why there has been a resurgence of interest in open baffle designs, I take the following as an initial starting point. In the modern era, enclosed speakers dominate sales, and the percentage of the market they represent at any given time probably varies some, but not much. The remaining market share is distributed among the alternatives. Roughly, the alternatives tend to reflect two somewhat different listener preferences:  one that is drawn to the dynamism and drive of live music and another that is drawn to an unencumbered and immediate engagement with the music.

Listeners drawn to dynamic realism and music's driving force are likely to be drawn at some point in their listening experiences to horns, whereas over the course of their audio history, those who favor an unencumbered and immediate personal engagement with music find themselves enamored of dipole designs. There are other factors of course, including the desire to employ lower-powered tube amplifiers, the relative cost of securing power/wattage or current, not to mention the natural desire for a hobbyist of any sort to want to experiment.

It's a bit harder to explain why, at a particular moment in time, those falling in these respective camps choose one kind of speaker over others, but it would be a mistake to overlook the importance of branding. Horns have long been associated with famous brands, from Western Electric to JBL to Klipsch. And planars have been associated with Magnepan and Apogee among others; electrostatics with Quad and Soundlab. In contrast, there has been no widely known brand leader that has carried the torch for open baffle designs, and thus no elephant in the room new designers would have to fight for market share. In addition, the cost of entry into open baffle designs is, relatively speaking, lower than it is for planar magnetic, electrostatics, or horns.

Another advantage is that while planars and electrostatics make serious demands on power or current and present challenging and unfriendly loads to amplifiers, open baffle designs typically present a small footprint and a friendly load. So it is not surprising that someone like me, for example, whose musical aesthetic encompasses both the quest for dynamic realism as well as an unencumbered, personal, and immediate form of musical engagement, would be drawn to both horns and open baffle designs as both create friendly loads. In my case, I am also blessed with a large listening room that can accommodate larger horn designs as well as more room-friendly open baffle designs by the likes of PureAudioProject.

The main acoustic feature of an open baffle/single panel design is that the sound radiates in a figure 8 manner. One can visualize the pattern most easily in three dimensions by imagining the number 8 lying flat on a piece of paper and imagining the baffle with drivers affixed arising straight up from the paper where the two identical circle-like forms meet.

The sonic advantages of this configuration include the capacity to project an open and airy soundscape that is denser, wider, and deeper than is normally attainable from a box speaker of any sort. Throw in the elimination of side wall initial reflections, and the previously mentioned absence of internal box distortions, and what one is left to enjoy is a musical experience that is invariably natural, relaxed, unforced, appropriately vivid and immediate, and never overwhelming.

What's not to like, or to put it another way: why wouldn't one give open baffles a try?

Indeed.

What Is Special About The PureAudioProject Duet 15?
Part I: The offerings, purchasing, and assembly.
Frankly, just about everything. Let's start with the line of speakers PureAudioProject offers. All the designs are modular in construction. CEO Ze'ev Schlik and his team design their offerings from scratch and choose precision parts accordingly – both in terms of their individual quality and how they perform with one another. They design individual speakers around the modular platform and request modifications in parts – especially drivers – as necessary for application in an open baffle configuration. The team identifies a wide range of speaker options that feature the parts they have chosen in several combinations that the end user can alter over time.

The Duet 15 currently under review features the aforementioned 15" woofer along with the extraordinary Voxativ Pife full-range driver (that one might normally expect to see in a single driver horn speaker of the sort prominently displayed on the Voxativ website), connected by a first-order crossover that can be arranged to operate either in parallel or series by the end user.

Note: Voxativ upper driver seen here, the review used Pife.

Other speaker options include two woofers and a Voxativ driver, either the standard or the Pife, or the Field Coil horn, arranged in D'Appolito configuration. The same configurations are available with a coaxial driver replacing the Voxativ.

Recently, PAP has introduced a speaker that features the famous Heil tweeter matched with two modified (for open baffle loading) 10" woofers made for PureAudioProject by Morel. The end-user is free to let their imagination run (relatively) wild. Modularity provides one the opportunity to make parts replacements fairly easily among some units. The two easiest post-initial purchase modifications are probably the addition of a second woofer in a second panel placed above the standard Duet 15 configuration and replacing either the full-range standard Voxativ driver for the Pife or the horn (and vice versa).

Upgraded internal wire changes are easily managed as are crossover unit changes that may be required by changes in driver complements. In one sense someone purchasing a PAP speaker secures not just an outstanding speaker but a platform on which to experiment, or, if you like, a canvas on which to paint music calling upon a somewhat different palette.

When one purchases a PureAudioProject speaker, one is not only securing a wonderful and versatile speaker; one is gaining access, in effect, to a speaker platform, on which several different speakers can be constructed. This provides the end-user with what may well be the most versatile speaker in commercial production.

Speaking of commercial production, manufacturing, and distribution. Speaker options are evolving, but for custom choices, all are available on the website. Purchases are also made on the website. PureAudioProject is an online company and then some. They do not have one central warehouse in which parts are stored and units assembled, from which they are then shipped worldwide. PAP uses the fact that their units are modular and sourced from around the world (literally) to avoid the additional steps of:

1. Having all parts sent to a central warehouse

2. Stored there sufficiently to create an inventory

3. Assembled and shipped from there to end users. All components and parts are drop-shipped from their respective manufacturer warehouse or PureAudioProject-owned warehouses in the USA or Germany.

Assembly And Setup
I received four separate shipments over a several-week period. Drop-shipping provides huge savings, a considerable percentage of which is passed on to the consumer. As a result, PureAudioProject's open baffle loudspeakers are not only versatile and musically captivating; they offer exceptional value to audiophiles and music lovers alike.

I had expected to receive a fully assembled speaker for review as I assumed that Ze'ev would want the review sample to be assembled flawlessly. I am not capable of flawlessly assembling any physical product. It is an open question whether I can assemble any product without endangering myself, let alone its potential for performing as intended. I indicated my concerns to Ze'ev who was unmoved, for two reasons. First, he wanted me to review not just the speaker, but the loudspeaker's experience which includes the fact that the end-user is responsible for assembly. Of course, an end-user may pay someone more adept than them to put the speaker together if they are unsure of their ability to do so. Second, Ze'ev wanted me to assess the relative ease or difficulty of the assembly process.

Both were reasonable requests with which I complied, but not without considerable trepidation.

I am pleased to report that the instructions were clear, precise, and easy to follow. Parts fitment was flawless and required no adjustments. The process is straightforward from unpacking to final assembly. Not an old hand at such matters, I was able to complete the assembly of both speakers in under five hours, and that included taking time off to pray that it would all work once completed. This prayer has become a ritual for me whenever I undertake assembling anything for over 40 years now, all stemming from my spectacular failure to assemble a Dynaco power amplifier. Once my build of the Dynaco was completed (the standard of which was that no parts were left unaccounted for) I called my wife into my office. I had toiled for weeks on the project to witness my plugging it in and turning it on for the first time – only to have the entire unit implode and set my office on fire.

To my surprise, relief, and unimaginable joy, when I put the speakers into my system, they worked. No fires, no explosions, and no laughter from my skeptical wife who was compelled to express her shock and modest admiration of my achievement.

If I can do it, so can you.

Readers of mine know that I do not follow the convention of reviewing components in the context of a reference system.  I do have a system that I have put together over time for myself with which I live quite happily because of its ability to present a musical experience that I find compelling, emotionally as well as cognitively. My system serves my ends which include a desire to seek and find refuge, insight, enjoyment, and education in my listening.

When I say that I refuse to employ my system as a reference, I am drawing attention to my view that it makes little sense to me to take a component I have been asked to review, say a speaker, as is the case, here, and simply put it into the system while removing my speakers and holding everything else constant. At best, such an approach would simply tell me how the speaker under review performs with other components that I have intentionally chosen for the very different goal of finding components that work well with my loudspeakers.

Instead, my goal is to construct a system around the product under review (as best I can) that displays the review component in its best light: that to the extent possible provides a musical presentation in my home that the manufacturer or designer would identify as what they had in mind from the outset, or, at the very least, that they felt would be recognizable to them as what their product is capable of. I have zero interest in looking to see how a product measures up to what I listen to on my own time. My interest is in seeing if I can uncover what the product is capable of providing by way of a musically persuasive and convincing performance.

The fact that I had considerable experience with open baffle speakers helped with speaker setup in my room and with the initial choice of equipment with which to pair the speakers. Initially, I paired the speaker with the Well-Tempered Amadeus Jr turntable set on a separate and highly recommended Nokturn stand, Mytek's original Brooklyn Bridge Streamer, the Lejonklou Entity Phono Stage and the Jadis DA88S MkII integrated amplifier that I raved about in a recent review. Interconnects and cabling were a mix of Auditorium 23 and earlier versions of Linn silver interconnects. Over time, I employed other combinations of equipment, including the Lejonklou Boazu integrated and the second iteration of the Brooklyn Bridge.

It is commonplace that open baffle speakers suffer from a cancellation problem that is a consequence of the dipole design. This is of course a theoretical claim and one that may often turn out to be the case in practice. Whether it does turn out to be the case depends on whether the designer has taken steps in modifying the drivers or the 'enclosure' to meet the challenge. Full cancellation effects would certainly be detectable and undesirable.

PureAudioProject's engineers are fully aware of the potential of cancellation effects the fact is that open baffle designs have come a long way over time, and I suspect that no designer of a modern iteration of them remains unaware of this major challenge all such designs face in principle. I would be surprised if steps haven't been taken by all such manufacturers to obviate the problem. I can report, however, that the PAP Duet 15 did more than obviate the problem. To my ears, they effectively eliminated it.

Eliminating the cancellation problem had a salutary impact on speaker placement. For all their seeming simplicity, it turns out that as a general matter open baffle speakers can create placement challenges as well as opportunities. Because they are dipoles placement can allow soundstaging opportunities that front-firing speakers are incapable of. This is most apparent in the potential for a remarkably deep and wide soundstage.  Toe-in can impact the width of the soundstage behind the speaker but also risks creating an imbalance in the width of the depth behind the speaker compared to a narrower width being cast in front of the speaker. Potential cancellation effects can render the soundstage behind the speaker diffuse and throw off tonality and overall dynamics. When it comes to set-up, the typical open baffle design is not without its challenges.

Whether due to the wizardry in resolving the cancellation effects or to the general design, the initial speaker setup was easy, leaving only fine-tuning as the listening sessions progressed over several months. I set the speakers in my room 9' from the back wall, 8' apart measured tweeter to tweeter, and with modest toe-in that fluctuated depending on my listening position between 3 and 6 degrees. I found two locations in the room that proved ideal for listening: a near-field position 6' from the speakers and a far-field position 14' from the speakers.

What Is Special About The PureAudioProject Duet 15?
Part II: Listening to music.
For some time, have harped on a distinction between sound and music. Every period in audio is defined by a distinctive sound, a preferred kind of sonic presentation. Asking someone whether they like the sound their system produces is very different from asking them whether the presentation is musically convincing, emotionally demanding, or narratively informative.

My impression is that among audiophiles of this era, the preferred sound emphasizes extremely low noise floors, see-through transparency, and, to my ears, an artificially hyped-up detail that is reminiscent of super high-definition television. Some of these attributes, to some degree, contribute to creating a credible musical experience. But they are not ends in and of themselves, certainly not from a musical point of view. At the extreme, they are distracting artifacts that take us farther away from the music, relegating us to taking pleasure in being observers of the experience rather than active participants in it.

The same point can be made slightly differently. We can hear something that sounds absolutely beautiful, stunning even, and find it seductive, relaxing, even gorgeous, yet find that it conveys nothing to us. By that, I mean it fails to provide insight into the composer's intention, or into the interaction among the performers – the key element of what constitutes making music together (as opposed to playing in the same setting individually. It can sound gorgeous yet fail to convey emotional meaning or narrative content. It's beautiful, but empty, much like the Cosmopolitan magazine issues of the 80s and 90s.  We learn nothing from it.

The main problem with the focus on sound rather than music is that producing a desired sound is largely a technological achievement, whereas conveying the musical content in ways that express emotional or cognitive content or that allow us to see into the performance is an artistic achievement.

I seek the latter when I listen to music, not the former. Don't misunderstand me. Aspects of the former contribute to the capacity of a system to produce the latter, but their value is entirely instrumental. When, as is too often the case, the former becomes the widespread benchmark by which we evaluate our systems, audio components tend to sound far more similar than different, and we are likely to grow more tired of them more quickly. We are drawn to new sonic experiences, rather than to securing new or deeper aesthetic, emotional, or cognitive insight.

And it is here that the PAP Duet 15 loudspeaker shines. To be sure, the sound it produces with every amplifier with which I combined it was clear, focused, relatively well extended, and sufficiently vivid or present. All of these features made listening enjoyable, whatever the medium – analog or digital. It was also revealing of the sonic differences between the two.

Final Thoughts: PureAudioProject Duet 15 Loudspeaker Review
What sets the PureAudioProject Duet 15 loudspeaker system apart from the vast majority of speakers that I have listened to at length is its way with music. Analog performances in particular, and especially when mated with the Jadis DA88 S MkII (now that's a mouthful) are fully resolved and presented as a coherent whole. It is one thing to enjoy a listening experience; it is quite another to be of a piece with it, to be informed by it, and to be grateful for what one has learned as a result; and for this to occur in an environment that feels unencumbered by constraints, appropriately liberated to speak one's mind, while inviting not rapture, but conversation.

The PureAudioProject Duet 15 loudspeaker is capable of intimate conversation and a very personal and comforting touch. At the same time, it can inspire exaltation and unbridled emotional release. It plays music of all types convincingly. It literally opened up my playlist. For nearly three months, night after night I found myself playing everything from Coltrane to Cooder, from the Roches to the Replacements, and from Beethoven to Oingo Bongo. Even more tellingly, I experienced a real joy in sharing my listening experiences with my wife and virtually every visitor to our home, including a former law school colleague of mine who loves music but normally does not partake in long listening sessions.

And when my son and daughter who had made up one half of the NY-based pop band, Murder Mystery, visited to celebrate my birthday, they were so taken by the system that they allowed me to play their first album on the system. They have never let me play their music in their presence before. Never. I think I detected a smile on their faces.

The PureAudioProject Duet 15 open baffle loudspeaker, fitted with the remarkable Voxativ Pife full-range driver, is my current benchmark for what contemporary open baffle designs are capable of – musically. If you are looking to find an amplifier match for them that could easily develop into a marriage, you might want to consider the Jadis DA88 S MK II vacuum tube stereo integrated. You will be rewarded with a musical presentation that will fill your heart with joy while deepening your understanding of the importance of music to the human condition.

If, as John Sebastian says, "the magic is in the music," then the PureAudioProject Duet 15 is a magical speaker, because it makes music, seems to get a good deal of pleasure in doing so, and invites the listener to join in the experience of it.

Specifications
Type: Open baffle loudspeaker
Frequency Response: 29 Hz to 20 kHz (in a typical room)
Sensitivity: >96dB/W/m (in a typical room).
Nominal Impedance: 8 Ohm
Typical Distance From Rear Wall: Two to four feet 
Distance From Side Walls: Any
Size: 21.25″ x 40.9″ x 10.63″ (WxHxD)
Weight: 44 lbs or more each.
Price: Starting at $8,490

Company Information
PureAudioProject
Voice: (877) 927-2233
Europe: +49 69 2991 7675
E-mail: info@pureaudioproject.com
Web: PureAudioProject.com