My first experience with open-baffle speakers was a few years ago, in Bangalore, India, in the showroom of ARN Systems, which then distributed the speakers made by Emerald Physics. I recall the sound of Emerald’s CS2.3 speakers as being exceptionally dynamic, nearing concert-level realism with a humongous soundstage that filled the large room. The Emerald CS2.3 was designed by Clayton Shaw, who has since moved on and now is the principal of Spatial Audio, based in Park City, Utah. (ARN is Spatial’s Indian distributor.)

Spatial Audio Hologram M1 Turbo

Why open-baffle? When I asked Shaw via e-mail, this is what he had to say:

Open-baffle (OB) design has been an area of research since about 1988. Prior to [Siegfried] Linkwitz, there was very little engineering information [about OBs] available, so a lot of trial and testing was required. The primary reason for my interest in OB initially was the feeling that I could hear the bass instrument itself without the overlay of box artifacts. The tautness and detail of bass instruments was very compelling, along with being able to distinguish multiple instruments playing simultaneously. Along with that, the advantages in the midband were very evident, with a more natural, breathing soundstage, and low coloration on voices and piano. I decided to take a long-term development approach, and made incremental improvements as more knowledge was gained through testing and experimentation.

From a first, quick listen to the subject of this review, Spatial’s Hologram M1 Turbo open-baffle speaker ($4000 USD per pair), it was clear that Shaw had brought all of this knowledge and experience to bear on its design. But I’m getting ahead of myself . . .

The Hologram loudspeaker system

Spatial has two series of loudspeaker models: Hologram and Lumina. The Hologram series, which can be considered the entry level, comprises six models, the M1 Turbo sitting just below the top model. Each M1 Turbo arrived in packaging of exceptional quality: a cardboard carton, inside that a box of thick foam, and inside that the speaker itself. The review samples were finished in matte Black Satin (the M1 Turbo SE is available in Black Gloss for $4500/pair). Each speaker is only 3”D (not including the protruding magnet) and 36”H x 20”W, and sports two large 15” midrange-woofers mounted flush with the flat baffle. As is typical of OB designs, the driver baskets and associated components -- the diaphragm, magnet, lead wires, etc. -- are all exposed on the rear. The baffle itself accounts for the speaker’s 3” thickness and comprises five layers -- MDF, aluminum, polyethylene, aluminum, and MDF -- bonded with vibration-damping glue. The MDF is a high-quality type from Plum Creek. The result is a panel that is extremely rigid and very dead to vibrations. The baffle’s front edges are beveled to create a visually pleasing appearance.

Packed separately in each box is a wide-bandwidth compression driver with ferrofluid damping. This must be screwed into the back of the upper midrange-woofer, and the provided speaker leads connected. The speaker’s single support leg -- essentially a metal rod -- must be inserted into a hole in the bottom of the rear panel, and spiked feet screwed into the bottom of the panels. Also on the rear panel are two high-quality, five-way binding posts, for the speaker cables. Assembled, the M1 Turbo is fairly compact and stands about 3’ tall and 16” deep, including the support leg, and weighs a substantial 48 pounds. It tilts back slightly; the spikes can be adjusted to slightly increase the height.

Spatial Audio Hologram M1 Turbo

I found the M1 Turbos quite pleasant to look at. All that’s visible on the baffle are the cutouts for the two 15” drivers, covered by a fixed grille, and the Spatial logo engraved at the bottom, highlighted in an attractive silver finish. The crossover uses Spatial’s Hologram Interface Technology, which Shaw described as a unique passive circuit designed to seamlessly blend the outputs of the twin midrange-woofers and compression driver at a frequency of 800Hz. He also said that this low crossover frequency permits the use of 15” drivers without compromising the reproduction of the midrange.

Shaw described the two-way design of the M1 Turbo as a dipole with controlled directivity that produces an 80-degree pattern of sound that drops off quickly beyond that point. All of this, he said, allows the listener to hear more of the speaker, and less of the mix of the speaker and the room. The M1 Turbo’s specifications include an in-room frequency response of 32Hz-20kHz, +/-3dB; a high sensitivity of 95dB/2.83V/m; a nominal impedance of 4 ohms; and a recommended range of amplification of 10-200W RMS.

Setup and positioning

The Hologram M1 Turbo’s owner’s manual includes detailed recommendations for positioning not only the speakers, but also where one sits to listen in the farfield or the nearfield. To determine the speakers’ optimal distance from the front wall, Spatial recommends that you experiment with positions anywhere from 18 to 36 inches. When I asked Shaw about this, he explained that open-baffle and closed-box speakers load a room differently. OB speakers’ bass output actually increases as they’re moved farther from the wall behind them. Directional bass doesn’t excite room modes in the horizontal and vertical dimensions, thereby reducing room excitation by two-thirds. As OB speakers are moved closer to the front wall, that proximity causes more cancellation effects in the low end, as zones of low and high air pressure bleed around the edge of the baffle and reach equilibrium -- which diminishes the level of audible bass. Shaw told me that experimenting with the speakers’ distance from the sidewalls is also required, to fine-tune the lower-midrange response: the M1 Turbos’ output between 200 and 800Hz increases with their proximity to the sidewalls. Regarding toe-in angle, Shaw suggested that the M1s be first positioned to fire at the listener’s ears; the angle can then be adjusted in or out to achieve the best soundstage and imaging. In my room, the best positions were 2’ 6” from the front wall, 1’ 8” from the sidewalls, and 8’ apart, the speakers toed-in so that the drivers fired at my ears as I sat in the listening position, 8’ away. I and the speakers thus formed an equilateral triangle -- one of the arrangements endorsed in the manual.

Spatial recommends giving the M1 Turbos at least 24 hours of run-in before doing any serious listening.

Amplifier matching

With a high sensitivity of 95dB, optimal matching of the Hologram M1 Turbos and their amplifier will be required for best sound. I had on hand two very different amps: the first, in my main system, was a Symphonic Line Kraft 250, a bruiser that puts out 400Wpc into 4 ohms; the other, in a secondary system, was a Belles Soloist 5, which provides 110Wpc into the same load. The Soloist was the better match for the high-efficiency M1s, mainly in terms of loudness control and gain matching to the preamp. While the Holograms sounded excellent through the Kraft, they were too loud even with my preamp’s volume knob set at 8 o’clock, which made it very difficult to achieve a comfortable listening level in this diminished gain range. I would imagine that tube amplifiers, with their modest power outputs, will also work well with the Holograms.


I was eager to test the bass slam of the Holograms’ four 15” drivers, but was anxious that they would be too much for my small (14’ x 12’ x 8.5’) room. Indeed, in the past, even some small floorstanding speakers with only 6” midrange-woofers have not blended well with this space. So it was with some trepidation that I cued up drummer Stanton Moore’s Conversations (16-bit/44.1kHz WAV, The Royal Potato Family/Juno). “Tchefunkta” opens with Moore’s drums, and the gut-busting impact of the kick drum was electrifying. The bass was well extended, with no overhang or woolliness -- just tightness and pace. I’d never heard bass quality like this in my room from a subwoofer, let alone a pair of small floorstanders. Evidently the credit goes to the Hologram’s OB design -- there were no box resonances to mess with the room modes that cause unruly bass. And when James Singleton’s double bass entered, its sound so convincingly energized the space that it felt as if he were right there, playing in my room. It was easy to follow the bass line in every track.

More strings -- these on Andy McKee’s solo acoustic guitar, from his album Joyland (CD, Razor & Tie 0552030005). In “Hunter’s Moon,” the transients of the plucked strings were rendered with excellent clarity and tempo, and no smearing or heaviness. McKee’s distinctive fingerstyle technique and hammerings-on were mesmerizing. Again, the total absence of box colorations reinforced my perception of an actual instrument being played in my room.

Spatial Audio Hologram M1 Turbo

I moved on, to women’s voices. The emotions expressed by contralto Lana Del Rey on her Born to Die (CD, Interscope 2793087) were very distinctive. In “Video Games,” she alternates between sounding mature and girlish, and these subtle nuances were well reproduced by the Holograms. The imaging was quite sharp -- Del Rey’s voice emanated from slightly behind a point precisely centered between the speakers, the accompanying instruments carving out their spaces clearly on the stage. I imagine that the coincident arrangement of the compression tweeter within the midrange-woofer aided this excellent imaging.

The soundstage of “I Can’t Tell You Why,” from Diana Krall’s Wallflower (24/48 FLAC, Verve), was spread across the width and depth of the room, the backing singers layered at the room’s rear and sides. True to their manufacturer’s name, the Spatials excelled at creating illusions of space. Their spectacular soundstages filled the area around the speakers, though I felt that the heights of those stages were somewhat curtailed. With “Gaucho,” from their Away from the World (24/44.1 FLAC, RCA), the Dave Matthews Band filled the entire front wall of my room, each instrument clearly defined, with ample air around it. Even when the mix grew dense with instruments, the Holograms maintained their poise, with zero congestion. I could pick out an individual instrument -- such as the violin slightly to the right rear of the stage -- and follow it with ease.

Spatial Audio Hologram M1 Turbo

“Why I Sing the Blues,” from Lee Ritenour’s 6 String Theory (CD, Concord 808678377170), includes vocals from guitar greats B.B. King, Keb’ Mo’, Vince Gill, and Jonny Lang. The unique combination of tonal modulations that distinguishes each man’s voice was showcased by the Holograms; particularly standing out was the soulful, evocative voice of the King of the Blues, B.B. King. Every voice sounded natural, without thickness or chestiness.

It was time for some jazz. Trumpeter Sean Jones’s impressive talent on his Im•pro•vise: Never Before Seen (24/96 FLAC, Mack Avenue) was beguiling to hear -- I reveled in this album’s excellent sound quality through the Spatials. In “60th & Broadway,” Jones’s horn was velvet-smooth, never harsh or brittle. The overall treble balance was well extended and silky, and hi-hat cymbals had the requisite amount of tizz, delicately shimmering as their sound died away.

I listened to more trumpet: Miles Davis’s A Tribute to Jack Johnson (24/96 FLAC, Columbia). In “Right Off,” Davis steps in with a searing solo that includes loud, powerful high notes. The dynamic range of this track through the Holograms was staggering. I’ve played this album many times, but it has never sounded better in my room.


When I switched to my reference Ascendo C8 Renaissance speakers ($10,000/pair), the first thing I missed, and right away, was the Holograms’ deep, powerful bass extension. The Ascendos go very low, and their bass was the equal of the Spatials’ in tautness and speed -- but it wasn’t as tactile. The Ascendos are a foot taller than the Spatials and project a higher, deeper soundstage, with better layering -- but the Holograms threw a wider, fuller stage, and more convincingly saturated the space around the speakers. Images were more precise through the C8s; the M1 Turbos, in comparison, could sound more diffuse. The treble, too, was more refined through the Ascendos, which better resolved details overall, to reveal more hues and nuances in the music. The C8s also better handled microdynamic shifts, while lagging behind the Holograms in terms of ultimate, large-scale dynamics. Still, this is excellent performance from the Spatials -- after all, the Ascendo C8 Renaissance costs two-and-a-half times more.


Before hearing Spatial Audio’s Hologram M1 Turbo, I’d pretty much given up on ever hearing deep, powerful, accurate bass in my small room. Well, I’m glad to report that now I’ve found one speaker that can not only dig deep, but do so with adequate texture, definition, and finesse, while offering adequate immunity from placement woes. Couple this with the Spatials’ expansive, open, airy soundstage, and throw in their staggering dynamics and smooth treble, and the Hologram M1 Turbos are one of the best models I’ve heard in this price range and beyond. If you’re looking for speakers that will give you nearly full-range sound while exciting the fewest room modes, that will throw a wall of sound while “disappearing” into the soundstage, and that will be easy not only to drive but also on the wallet, then I present to you Spatial Audio’s Hologram M1 Turbo.

. . . Sid Vootla

Associated Equipment

  • Sources -- Music PC running JRiver Media Center 19, M2Tech Evo hiFace USB-to-S/PDIF converter with battery power supply and master clock, Oppo BDP-83 universal Blu-ray player (used as disc transport)
  • DACs -- Ayon Skylla II, Line Magnetic 502CA
  • Preamplifiers -- Lamm Industries LL2.1 Deluxe, Parasound Halo JC 2
  • Power amplifiers -- Belles Soloist 5, Symphonic Line Kraft 250
  • Speakers -- Ascendo C8 Renaissance
  • Cables -- AudioQuest Cinnamon USB; Creative Cable Green Hornet digital; Kimber Kable Select 1011 interconnects and 3033 speaker cable; Audio Art Cable Power 1 Classic, Shunyata Research Diamondback power cords
  • Power conditioner -- Sine 30A
  • Room treatments -- GIK Acoustics 244 panels (6), Echo Buster panels (2)
  • Rack and speaker stands -- SoundFoundations
  • Listening room -- 14’ x 12’ x 8.5’, speakers placed against short wall

Spatial Audio Hologram M1 Turbo Loudspeakers
Price: $4000 USD per pair.
Warranty: Five years parts and labor.

Spatial Audio
6300 Sagewood Drive, H204
Park City, UT 84098
Phone: (435) 640 1294