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PureAudioProject Trio15 Coax10 open-baffle speakers Review

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Design considerations for the Coax10 version

Everyone in the speaker business is trying to make a musical speaker, which is a descriptor not very enlightening to the buyer. Various speakers that are claimed to be musical can vary radically in their technology and sound quality. Having said that, it is helpful to a degree to distinguish between a speaker that is precise, revealing, or uncolored versus one that strikes the ear as more organic, warm, and fatigue-free. These general distinctions are often upheld in assessment of different genres and brands of speakers. Rarely one sees that divergence when a company offers distinct models of speakers, as is the case with PureAudioProject.

I have to state the next paragraph cautiously; reactions in the audiophile community to particular comments in my reviews are sometimes overdone. Case in point, I had a conversation this past week with a cable manufacturer who is cautious about how they introduce new cables because so many hobbyists think that just because a new line comes out there must be something wrong with the previous line, as though it is defective or is invalidated by the new product. All I need do is say I prefer it to the prior line and a swath of audiophiles will think the second-place cable is unworthy of consideration. Some audiophiles are so hung up on having the putative best that they cannot fairly assess a line of products from a manufacturer.

When PureAudioProject seeks to introduce a new primary driver, they may encounter an issue that does not beset manufacturers who either use their own proprietary drivers or stay with one genre and brand of drivers. When PAP offers a suite of drivers of different technologies, i.e. horn vs. coaxial, there are inevitably primary differences in terms of performance. I have described some of these differences, but I caution against the conclusion that one or the other is held to be defective simply because the subset of characteristics is different. There will be audiophiles who, due to their priorities in system setup, music selection and preferences, will gravitate toward a two-way like the Horn1, versus the Coax10. The two systems yield distinct results, and it behooves the buyer to know what their preferences are so that they make a proper decision for higher satisfaction.


Design considerations of the Trio15 10” coaxial

In conversation with Ze’ev Schlick of PAP, he stated the design challenge for the Trio15 Coax10 as, “pushing the sonic performances to the edge while maintaining a musical experience that is organic, natural sounding, no fatigue and emotionally involving.” As above, that is what all speaker makers are trying to accomplish, but it is the chosen technology, the implementation in its different forms, that yields the thumbs up or thumbs down from the customer. The technological goals for the Trio15 Coax10 involved a point source design with drivers that are similarly constructed. To improve linearity and yield a homogeneous sonic signature, the driver was customized with an open, rigid cast basket and a purpose-treated lightweight paper cone. As a tie in to the well-received two-way performance of the Horn1, the same polymer soft dome driver with 1.4” throat was used. This allowed the woofers to be crossed over using a second order low pass filter at 200Hz and the 10” mid-woofer and horn tweeter to be crossed using a 4th order filter at around 2kHz.

In terms of voicing this combination, Ze’ev states, “The final voicing challenge was choosing the most natural sounding crossover components for that specific configuration. This process was dominated by long listening sessions to all possible genres. This was probably the longest of the three processes as every single component was sonically evaluated over a long period of time before the final choice was made. We ended up with the superb Mundorf Silver/Gold Oil grade capacitors (MCAP EVO SGO), the new Hi Rez Foil Resistors (M Resist ULTRA) for the mid woofer, the smooth sounding Metal Oxide resistors for the Horn Tweeter and Copper Coils with Foil Paper (VLSU) for the mid and high frequencies.”

As there are no off-axis drivers and the 10” coaxial driver carries the bulk of the frequency spectrum, the Trio15 Coax10 performs much closer to a true point source speaker than typical designs. Having used fine traditional designs, including products from Salk Sound, Legacy Audio, Chapman Audio, Von Schweikert, Daedalus Audio, Wilson Benesch and others, none of the speakers with multi-way drivers can pull off the tightening of the images that is possible with a coaxial driver. It is a function of the technology employed and is one reason why some enthusiasts insist on listening to nothing other than a full range speaker having one driver per channel. When comparison between the two technologies is heard in one’s home, or in direct comparison in a demonstration, the virtues of each design are appreciated and the hobbyist can select their preference. I see value in both technologies and design choices, which is why I pursue and continue to use both.

The Trio15 Coax10 does not accomplish the full range, single point source sound signature perfectly. It obviously cannot, as there are two huge 15” woofers flanking the 10” driver. The ear perceives this, especially when bass-infused music is heard. However, this is not a problem, except for those who are willing to eschew lower frequencies in search of a perfect point source sound. You simply cannot have it both ways; the closest you can come is with a speaker like the Tannoy Glenair, which I reviewed back in 2008. But like the Glenair, with the Horn1 you are making a more difficult match of the 1.4” polymer tweeter to the 15” woofer. It works, and to many persons’ ears is a splendid result. But, by necessity, it leaves some room for improvement in the midrange and mid-bass, and that is where the Coax10 shines.

One of my system-building principles is that unless absolutely necessary, I will not be without deep bass, and ideally not without LF, i.e. lower than 20Hz from high-resolution audio files. I see those frequencies as necessary to grasping the extent of the performance. If it is a choice between having the pure point source with only a 10” driver or the PAP design with assistance from the 15” drivers, I will opt for the presence of the 15” drivers, because elimination of the bigger drivers forfeits not only the reproduction of those low frequencies, but also the potential for the tactile sense created by deeper and stronger bass. I do not wish to have a large set of forward firing open-air headphones, but a speaker system!

Initial setup

The initial system and listening for theCoax10 about which the previous comments have been made was with the following setup, all components reviewed by myself for Dagogo:

  • Tidal premium level and Roon software (Note: software attenuation used in this setup by necessity)
  • Small Green Computer sonicTransporter
  • SONORE Signature Rendu SE with systemOptique


  • Clarity Cable Supernatural USB 1m
  • Eastern Electric Minimax Tube DAC Supreme
  • Legacy Audio i.V4 Ultra Amplifiers (two or four channels employed)
  • PureAudioProject Trio15 Coax10 Speaker
  • All power cables Belden BAV Power Cords
  • All interconnects Iconoclast Generation 1 SPTPC RCA
  • Speaker cables Iconoclast SPTPC jumpers and speaker cables


As the DAC is dedicated and without a volume control, I used the Roon software’s volume control. SONORE’s Signature Rendu allows for either fixed or variable volume, which is ideal for configuring all manner of systems with a direct signal from the DAC, whether it does or does not have volume control built in. I employed the patented Schroeder Method of Interconnect Placement, which doubles the interconnect (two conjoined interconnects) for superior resolution. I began by using two channels of the Legacy i.V4 Amplifier, but once I tried four channels and ran the speakers passively bi-amped I remained with that setup for the duration of the review period; once the superior method has been established, there is no point in reverting to the lower-performance setup.

A word about the fit and finish; it is commendable and consistent with previous versions, as discussed in the other reviews. As I had white panels, I opted for the white/black/white “domino” color scheme as the PAP site calls it. There are additional wood veneer finishes, such as German Oak, now available for an upcharge.


Commanding concentric driver

The Trio15 Coax10 is holistically a level up over the other iterations of the primary drivers I have used, and as aforesaid is similar to the Tannoy concentric driver of the Glenair. While assessing that speaker I was using the Jeff Rowland 501 class D monoblock amplifiers (500wpc into 8 Ohms; 1,000wpc into 4 Ohms). I heard that Japanese audiophiles were doing systems with high power and high efficiency speakers. I tried and appreciated! I had never heard such snap, vividness, instant transients and dynamics with the force of a dam seemingly bursting. I was sold on the idea, as you can see in that article. Now, fourteen years later nearly to the month, and I am back at it, and I like what I am hearing from the Trio15 Coax10 even more. The results with this system working with high power and high efficiency have moved distinctly toward the upper end of the performance spectrum.

This time I’m running my current amp champs, the Legacy Audio i.V4 Ultra, the only class D to unseat all previous tube and solid-state amps, and I do mean all. Go ahead, check my extensive amp review list. I wouldn’t go back for any of them to put aside the i.V4 Ultra. That is what you call an endorsement! I have built enough systems with enough speakers that, in my world, there would have to be a true tsunami of technological change to get me to spend more time with tube or solid-state class A or A/B amps. At this point my plan is to explore further in class D. Damn me for it if you wish; feel free to read another reviewer on amps if you think I’m washed up.

But I’ll tell you this; you’d be hard pressed to find the combination of stony silence, crazy power (think a minimum of 1,200 wpc and 2,400 wpc when passively bi-amping), and high current that comes in class D packages nowadays — at least not for a human with a normal paycheck or who has had enough lifting of well over 100-pound mono amps. I’ll be working in this review with the Legacy amps and the Kinki Studio EX-M1+, which I consider a standout due to good sound and exceptional flexibility (it is configurable in dedicated preamp, dedicated amp, and integrated amp modes).

12 Responses to PureAudioProject Trio15 Coax10 open-baffle speakers Review

  1. Waldo says:

    I like the way you think but after 40 years of system building I’ve learned to appreciate simplicity. I get over 90% of what you’ve built here for less than 10% of the price using Lii-15 full range drivers in simple open baffles, a Dayton 12″ sub, a super simple hand wired 2 watt SET amp and a Topping E30 DAC attached to my good old Oppo – 103D. With Blue Jeans Cables, the total cost was under $2K

  2. Douglas Schroeder says:

    God’s Peace,

    Thank you for the compliment! And thank you for sharing your system details.

    It appears your comments are subjective endorsement of how much you enjoy your system, and not a comparison of the two speaker systems in the same room and with the same equipment. With such vast differences between a 2 Watt SET and the Legacy Audio i.V4 Ultra, for instance, I do have thoughts in regard to the expected performance of your system, but I will not comment as I have not heard it.

    It is obvious you adore the sound of your system, so kudos on reaching pleasing performance!

    Douglas Schroeder

  3. Jim Widgren says:

    Your comment is much appreciated Waldo; I too believe that simplicity is a virtue (next to cleanliness and Godliness). I am going your rout and will order the Lii F15 today; I already have a Janis subwoofer for the bottom octave and many high-quality amps to play with. If I may ask, what SET amp design did you build? with what output tubes? Many thanks again for the purist & perhaps ascetic viewpoint!

  4. Paul Maier says:

    These speakers started out several years ago at around the $4000 mark. Now, just a few years later, they are running $8000+. Personally, I’d go DIY, or if not–Spatial Audio.

  5. Douglas Schroeder says:

    God’s Peace,

    You make a general statement in regard to the speaker without critical distinctions such as referencing the main driver and the crossover. The Coaxial 10″ is a fundamentally different speaker than the Tang Band version I reviewed six years ago or the Horn1, which is a two-way. The parts used in the crossover for the three-way Coax10 are higher quality than the original crossover and it is a more involved crossover to produce.

    Without a direct comparison preferences mean little. People can feel free to pursue a design with dual 15″ woofers and an approx. 1″ tweeter, which is closer to the Trio15 Horn1 version, but this should not be seen as equivalent to the fundamentally different Coax10 version. Persons who pursue any design using twin 15″ drivers and an approximately 1″ tweeter will NOT get performance in several parameters similar to the Coax10. Having heard in my room a two way Emerald Acoustics design which more closely modeled the Spatial Audio, in my use and recollection such would not compare well with the Trio15 10″ Coaxial in terms of frequency smoothness, midrange bloom and macro-dynamic capacity overall. I could have bought the EP speaker, but returned it for those reasons. I have no plans to part with the Trio15 Coax10 because it performs holistically superior.

    In my assessment of the comparison of the Coax10 design to ones that have twin 15″ and 1″ drivers I do not have to hear the competitor speaker to make my general assessment, as it is based on hard design and physical performance limitations (i.e. drivers) of speakers’ designs. Going beyond such analysis, however, without a direct comparison, is unwarranted. Audiophiles can make whatever claims they wish, but the readership should understand that often they are unsupported.

    The primary grievance which surfaces regularly in such reviews is about the cost. It’s pretty simple; if you build it yourself, you have all but assured you threw your money away in terms of recovering it at resale. You also likely lack the means to build a speaker as aesthetically fine as a manufactured unit. Some people do not care to have a garage build in their living room. Finally, given that in all likelihood there would never be a direct comparison between a home made speaker and one such as the Trio15 Coax10, the suggestion that the DIY speaker would perform as well is a fantasy without basis.

    I am not interested in a protracted discussion about the merits of the Trio15 Coax10 or of DIY. My assessment of performance based on the differences between the two designs is more widely applicable regardless of brands.

    Douglas Schroeder

  6. Jörgen says:

    Great review !
    I might simply follow your footsteps relative to both amp and speakers.
    Now, I believe you were using a 4 channel amp … if so (and even if not) … could you bi-amp and introduce room-correction a la Legacy on the bass only ?

  7. Douglas Schroeder says:

    God’s Peace,

    Thank you for the compliment!
    It would be much simpler to do the passive bi-amp setup that I worked with in the review. The advantage of using identical channels is simplicity, the same output of the amp for all four channels, and the same resolution, tonal and soundstage characteristics for all the speaker inputs. When using a combination of two stereo amps to get four channels there is no predicting what result will occur or if it will be agreeable.

    As to the use of the Legacy Wavelet processor, I think in theory it could work as you suggest, but I would contact Legacy Audio to discuss that possibility. I have heard of others using the Wavelet with different brand speakers, so perhaps it could work in this situation.

    Douglas Schroeder

  8. Phil says:

    Doug, You cannot compare how Claytons Emerald Acoustics speakers from days past sound today with the new Spatial Audio speakers be it the Shappire series or X series. You need to review a pair so you have real knowledge of their performance, which was so good I sold my Quad speakers which I had for 10 years.

  9. Phil,
    God’s Peace,

    I was at AXPONA all three days and returned yesterday after the show. While there I heard the Spatial Audio Hologram briefly. Its sonic footprint was as I had expected and described above in general comparison to the PAP 10″ concentric, as would be expected by the design parameters. It immediately called to mind the older Emerald Physics design about which I made my comments above. At the show I heard at least one or two other designs utilizing a diminutive tweeter with larger woofer(s), and they also carried the sonic signature that I describe above versus the larger coaxial of the PAP 10″ Coax. That is a result of design and driver considerations, and those who are familiar with such do not need a direct comparison to know it. Above I was not suggesting that I have complete familiarity with the current models of Spatial Audio, but rather was discussing the performance characteristics of such designs.

    After listening for a few minutes to one of the versions of the Spatial Audio Hologram and hearing the distinctive characteristics I have mentioned above, I made the decision to not seek a proper demo and chose not to pursue it for a review. It is possible that had I conducted a proper demo, I might have changed my mind. However, I have no interest in debating my decision, nor debate over how closely the Emerald Physics and Spatial Audio designs compare.

    If you were the owner of vintage Quad speakers, I am not surprised that you sold them after hearing OB contemporary speakers. My long term conclusion in regard to the older Quads, after hearing them several times, is that they are in today’s market unimpressive. Aside from their undeniable nostalgia I would not own them. Unless, quite literally, someone wished to give me a pair. I have a set of the coveted Ohm Walsh Model F’s because they were going to be taken to the dump and someone recalled that I like gear. I saved and had a bit of work done to resurrect them, so I have those vintage speakers for fun, not for critical listening. I do not tend to keep vintage gear as to my ear it underperforms more contemporary designs. I heard the vintage Wilson WAMM at the show, which was a real treat! I appreciate the speakers, amps, EQ, etc. being brought in for the public! However, I knew quickly that I would not own it, for I would not listen to it, again, because it has what I consider fatal flaws in performance compared to what is done with larger towers today. The ’57 and ’63 Quads have serious performance compromises, among them pitifully low wave launch resulting in a sunken soundstage, and no appreciable low end extension. I believe that for most speakers that are compromised in bass extension the purported superior midrange is not actually superior, but simply stands out as there is no appreciable bass to consider. I have a similar effect that occurs when I use the Wharfedale Opus 2-M2 speakers with their glorious 3″ soft dome midrange. It is not difficult for contemporary designs to holistically outperform vintage Quads. The one important variable that could push someone to get the vintage Quad is the coherence combined with ESL sound. For some people, that is enough of a cause to own them.

    In terms of larger, far more capable ESL speakers, I prefer to use a full range speaker such as the King Sound King III. As to the larger Quads of several years ago, if I recall correctly, I contacted the distributor to arrange for a review but I never heard back. I will neither confirm nor deny the rumors of reliability problems, but I am content that I did not conduct the review. I feel my time was well spent on the review of the Sound Lab Ultimate 545.


  10. Jim Tutsock says:

    Douglas, I, for one, would appreciate a copy or at least a number for that patent you purport to hold. Those attorneys can be fierce.
    I’m slowly in the market for my 20 year changeout of equipment so I am enjoying my education and remain utterly and satisfyingly confused to this very minute. I guess I will have to get my butt to Capital Fest, but the last time ( 7 years ago ?) my ears gave out way before the minutes and seconds. I had a stapedectomy performed in each ear in the low 90″s and that will bring on tinnitus or so I was semi-recently told; enough concerts and the like (not to mention previous housebuilding, related construction work and now a certain medication) to bring it on anyway. Strangely I enjoy listening to music even more and think I’m better at it. You are in a top class of reviewers (if, where else, only for your patient and complete replies to commenters, sheesh!) and I have numbered many this trickle of years. 2 questions: Stand mount monitors at their best can easiest perform the disappearing act that I need for my enjoyment. Open baffles are supposed to be good at this but I don’t always see it addressed and I mention it here because I’m not sure you did or maybe I need to read all of the earlier reviews to find it. Also the coax driver (which for some reason I was always a big fan of back to my car stereo days) in these designs seems low in relation to ear height and I have read that this will make for reduced image height, even if it’s angled up to reach ear height, but I’m sure you would not have gotten to this far a traverse with this speaker arrangement if that was the case but still wondering…. lastly when Axpona spent one year in Atlanta (06 or 7) I heard the original Voxativ that they now do as a diy kit and boy was that something different and magical. They have come a long way and would like to hear PAP and them in the same time frame at similar $. (or $$+). Jim

  11. Jim,
    God’s Peace,

    “… that patent that you purport to hold.” I worked in collaboration with an IP attorney to get the patent. The patent has been issued, but I’m not interested in addressing questions which are on their face incredulous. I also have no interest in debating with anyone the technical or sonic merits of the Schroeder Method of IC Placement. There are those who try and those who talk. Those who try find it to work. For the record, here is the article:

    I also discussed it at length on Audiogon:

    FYI, I dropped all participation on Audio Asylum years ago, and Audiogon more recently as I found involvement to have diminishing merits over time. Ergo, I have no idea what the threads say recently, and I don’t care much.

    In the review here I didn’t address the topic of “disappearance” of the speakers because my perspective is that the ability of the speaker to disappear has far less to do with speaker type and far more with the complexion of the system and setup of the speakers. We may disagree on that, but it is one reason you do not see me saying of all sorts of speakers that they disappeared, as though it’s a mandatory phrase to have a good review. The audiophile is not building a very good system if the speakers do not disappear, and I have found that is true of every type of speaker and regardless of size. I have 5.5′ tall, 30″ wide King Sound Electrostatic speakers that disappear as well as any bookshelf I have ever used. So, I’m not in agreement with the characterization that bookshelf speakers inherently image better than larger speakers. I have reasons for that perspective beyond comparison of dozens of models, but I am not discussing it further now.

    You are correct in your assessment of the relative height of the coax, or any other primary driver in the Trio15 line. Angling the baffle slope back helps, which is why I suggested to PAP that I use hockey pucks under the front to address that somewhat. PAP took my idea and have their own special hockey pucks for that use. I’m flattered that my opinion mattered.

    That’s a pretty strong judgment, “but I’m sure you would not have gotten to this far a traverse with this speaker arrangement if that was the case,” which makes me think this is more of an issue for you. Conversely, many are not terribly bothered by the lower orientation of the midrange relative to the ears. Witness the plethora of sub 4′ smallish tower speakers. I prefer very sizable speakers when possible, but that doesn’t mean smaller ones are without merit. If the baffle slope solution is not agreeable, the alternative solution is quite simple; elevate the speaker. You can do so with the Landscape Orientation that I use extensively, which in my case required specialty Sound Anchor stands which are not cheap (however, PAP has changed the metal frame for the Trio15 which makes it a more difficult proposition), or you can find some base to set the speakers atop. It’s a simple way to change the orientation and gain the ear height, or even in some cases, slightly above ear height one might desire. Now, if one wishes to debate the efficacy of such a base, I’m not interested. Such things are not resolved from armchair discussions, but from trials. 🙂

    As nice as the Voxativ model I reviewed sounded, I holistically prefer the coax. It mates superbly with the twin 15″ woofers.

    Douglas Schroeder

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