Steven Stone is the former editor of AudiophileReview.com. He a longtime audiophile and home theater writer, as well as a musician and recording engineer. Steven has written for publications like Stereophile, as well as HomeTheaterReview.com, AudiophileReview.com, and The Absolute Sound.
Steven is plays guitar, mandolin, and Ashbory bass and is a collector of fine musical instruments.
Nowadays the words "compression horn" aren't bandied about much when discussing home stereos. Conversely, the term "unique" has become quite common in gear descriptions; in fact, many folks seem to believe that "most unique" is proper English usage. It's not. Many of the components that get the "most unique" title aren't all that special, but what if I told you there was a new speaker that does qualify as unique (not most unique or very unique) because it combines old technology in a new way to create a more room-friendly loudspeaker that interacts less with a room's acoustics than most conventional loudspeaker designs?
This is what you get with the latest offering from Spatial Audio, the M3. It's a loudspeaker that uses an open-baffle design combined with a compression driver in a coaxial arrangement to achieve a sonic result that is unobtainable from any conventional box, line-array, electrostatic, or even dipole design.
Spatial Audio is the brainchild of Clayton Shaw, whose first company, Emerald Physics, was founded in 1978. In the beginning Emerald Physics was a "project company" where Shaw worked on prototypes for his other clients, which included a number pro audio manufacturers. In 2006 Shaw took his latest proof-of-concept project to the Rocky Mountain Audio Show, where he met the owner of Underwood Audio, Walter Liederman. Liederman was so impressed by the prototypes that he encouraged Emerald Physics to build what came to be the Emerald Physics CS2, which debuted at the 2007 Rocky Mountain Audio Fest. By 2009 Emerald Physics had over 25 dealers, but Underwood Audio has sold the most speakers by far. In 2010 Shaw sold Emerald Physics and all its intellectual property to Underwood Audio and agreed to continue designing Emerald Acoustics loudspeakers for the next three years under a non-compete clause. The models 2.3 and 2.7 were Shaw's last Emerald Physics designs.
In 2010 Shaw also created Spatial Audio, whose first products were computer audio installations using Mac Minis and a software suite that combined sophisticated EQ with the ability to handle multiple channels of crossovers. I reviewed the Spatial Audio computer system for The Absolute Sound in 2012. In 2014, Shaw released the first Spatial loudspeakers, the M1 and M2, followed in 2015 by his latest designs, the M3 and M4.
This review will focus on the M3 loudspeaker. Its base Turbo model is priced at $1,995 per pair. The Turbo S version sent for review adds the latest Spatial M25 compression driver and ups the price to $2,595 per pair. Besides its unique design (which I'll explain in detail in the next section), the M3 has a 20-year warranty on parts. That's how confident Clayton Shaw is that his design, using drivers that were sourced from pro audio and sound reinforcement equipment makers, will withstand all the rigors of home use.
The Spatial M3 is a two-way design with the 800-Hz crossover point between its coaxial compression driver and its twin 15-inch mid-woofers. With an efficiency of 94 dB at one watt/meter, the M3 is a highly efficient design with a very even four-ohm nominal impedance curve that can be driven successfully by even a small-wattage power amplifier. The M3 is an open-baffle design that has no enclosure or box. Instead the two 15-inch-diameter drivers are mounted on a three-inch-thick baffle that measures 17 inches wide by 42 high. The M3's dispersion pattern is tightly controlled by the design to be 80 degrees horizontal and vertical over its entire frequency range from 32 Hz to 20 kHz.
To accomplish its high efficiency and controlled dispersion, the M3 uses a compression driver for its tweeter/midrange. A compression driver employs a different technology than a conventional dynamic driver. It is called a compression driver because the area of the loudspeaker diaphragm is significantly larger than the throat aperture of the horn to which it is attached. Horn-loaded compression drivers can achieve very high efficiencies, around 10 times the efficiency of direct-radiating dynamic driver loudspeaker. A "lens" in the throat of the horn extends and smoothes the driver's upper-frequency response, while the shape of the horn controls the dispersion pattern. Unlike loudspeakers that use a dome or ribbon tweeter, the M3 has the same dispersion patterns for its upper frequencies as its lower ones. When you walk around the M3, you will notice that the loudspeaker does not generate much sound from the back or sides. This is due to its open-baffle design, which actually cancels side sound while reducing the sound coming from the back. This is similar to what happens with an electrostatic line array, but the M3 does not generate as much sound to the back because the compression driver does not generate a portion of its output to the rear the way most electrostatic line arrays do.
Bass response in the M3 design is also different than with a conventional sealed- or ported-cabinet loudspeaker. Most loudspeakers' bass response is omnidirectional below 100 cycles or so and forms higher low-frequency SPL pressure levels around and behind the speakers themselves. However, an open-baffle design is different. With no cabinet or port arrangement to reinforce the bass frequencies, an open-baffle design does not generate the same pressure zones around the loudspeaker. Instead the bass is directional--it comes out of the front of the loudspeaker in a directional dispersion pattern controlled by the driver's diaphragm shape. This dispersion pattern interacts with the room far less than any conventional cabinet design's omnidirectional bass dispersion pattern.
One of the principal drawbacks of most commercially available off-the-shelf compression drivers is that they do not have linear frequency, especially in the 1,000- to 4,000-Hz region that is so critical for proper upper midrange response. Clayton Shaw got around this issue by using a digital EQ to correct these issues on his earlier Emerald Physics designs. For the Spatial M3, Shaw was able to work directly with a driver manufacturer to develop a compression driver with a different lens configuration that no longer needed digital EQ to keep it more linear in frequency response.
Setting up the M3 Turbo S speakers in my dedicated listening room was relatively simple. The previous loudspeakers were a pair of Emerald Physics CS 4.3 loudspeakers, and not surprisingly the Spatial M3 Turbo S models ended up with a very similar placement and toe-in. I angled the M3s so that they faced directly at the center listening position. I used the spikes that came with the M3 to anchor them firmly to the concrete floor under my carpet.
For most of the review, I used six-foot runs of Audience AU24SX speaker cable to connect the M3s to a series of amplifiers--including the April Music Eximus S1, NuPrime ST-10, Pass Labs X-150.3, and Bel Canto M600s. I also used WireWorld Eclipse 7 speaker cable during the review.
My main listening room has, in residence, a pair of JL Audio Fathom F-112 subwoofers that I usually use to augment my system's low bass. At first I tried a standard THX-type crossover setup using 80 Hz as the crossover point between the M3s and the Fathoms. After a few weeks I noticed that, while there was a lot of bass in the room (especially in pressure zones), I was not getting as much bass as I wanted at my listening position, so I tried something different. Instead of using the 80-Hz crossover that is built into my Parasound P7 preamplifier, I removed it from the circuit and gave both the M3 and the JL Fathoms a full-range signal. Then I used the Fathoms' built-in crossover to set them at 50 Hz. This forced the M3 to cover more of the bass region. Because the M3's bass is more directional, I found less bass build-up in the room's pressure zones and more bass getting to my ears.
Another advantage to using this crossover scheme is that it reduced the 60-/120-Hz low-level hum from the JL Audio Fathom subwoofer from barely noticeable to nothing. The positive effects of a completely hum-free system (even at extremely low volume levels) are myriad.
With most full-range speakers, especially less-efficient ones, you gain quite a bit of headroom by rolling off the low bass into a subwoofer. However, because the M3s are such efficient speakers with exceptional power handling (they are really hard to destroy via high SPL levels), there is no practical advantage to rolling off their low frequencies, except perhaps if you are attempting to use a five-watt or less power amplifier to drive them. In most rooms, using any amplifier that puts out more than 50 watts RMS, you should run the M3s full range so that you get all the advantages of their more directional bass presentation.
As you would expect from a speaker that is essentially a point source due to its coaxial tweeter/midrange, the Spatial M3 Turbo S speakers image as well as any loudspeaker I've ever used. If you like pinpoint imaging, the M3s deliver it in gleeful abundance. Take even the densest, most multi-tracked mix you own, throw it on your turntable or digital player, and you will be amazed and delighted by how easy it is to identify and follow each part because every instrument and vocalist has a particular location, firmly anchored in space. Not only can the M3s produce superb lateral localization, but with the right source material and power amplifier the M3s produce a convincing three-dimensional image. Of the amplifiers I had in house during the review, the Pass Labs X-150.3 had the most depth retention, followed closely by the new Bel Canto M600 mono blocks (which were among the quietest power amplifiers when connected to the M3s.)
I have a very quiet listening room with an average 35 dB of ambient room noise. This means that any extraneous noise coming from the system is noticeable. Because the Spatial M3 Turbos are so efficient, your electronics need to be quiet and noise-free. I found that quite a few of my older power amplifiers were not silent enough to use with the M3s. Both of my original Adcom GFA-535II power amplifiers had some low-level RF issues. For example, I could hear a radio station if I put my ears up close to the M3 drivers. With my Dyna Stereo 70, there was a low-level 120-Hz hum that was just loud enough to be distracting. Even my 17-year-old Pass Labs X-150.3 had a bit more hiss and low-level noise than I would have liked, spurring me to send it back to the company for a refurb. I did find three power amplifiers that were quiet enough to mate nicely with the M3s: the April Music Eximus S1s, the NuPrime ST-10, and the Bel Canto M600s. All three of these amplifiers are high-speed Class D variants with ultra-quiet power supplies and extremely good signal-to-noise specifications. If you, too, have a quiet room, you will also notice the M3s' need for low-noise electronics and front-end devices.
Although my room has gone through rather extensive treatments to reduce early reflections, standing waves, and other bass issues, I still found that the M3s' more directional bass yielded much more accessible bass than I had gotten previously with other loudspeakers. Blending the M3s' bass with the JL Audio Fathom F-112's low bass was easy, and the final results were as seamless as I've heard from a system that utilizes subwoofers. Molly Moore's new Shadow of the Sun EP has plenty of low-frequency EDM synth bass combined with electric bass. Through the M3 system, all of the bass frequencies were fast, tight, and big, yet they were always completely under control.
Because the M3s' drivers are basically modified pro audio components, they were designed to withstand high SPLs levels. And because the M3 Turbo S speakers are so efficient, they can play loudly with very little power. This means that these loudspeakers can, if you wish, deafen you with high SPLs all day, so some care should be used to ensure that you don't unintentionally blast yourself into tinnitus. Unlike most conventional dynamic speakers, which will have some additional distortion at higher SPLs, the M3s will play cleanly to well past any sane person's comfort level.
I'm a big fan of loudspeakers that use something other than a conventional crossover in the 1,000- to 2,000-Hz region, which is what you find on most conventional two-way dynamic loudspeakers. I use the crossover-less Audience 1+1 V2 loudspeakers in my nearfield monitoring system and also spend plenty of time listening to planar design headphones, which also lack a crossover. Although the Spatial M3 loudspeakers do employ a crossover, it's down at 800 Hz, which is below the critical upper midrange region. I found the M3s had a smooth and cohesive midrange character that I usually associate with a transducer system that doesn't have a crossover in the upper midrange region. Although I did not have a low-power, single-ended tube power amplifier to mate with the M3 Turbo S speakers, I suspect the combination would yield a midrange to die for.
I'm not a young buck anymore, and the last time I tested my hearing, anything above 14 kHz was a figment of my imagination. Still, I found the M3s' upper frequencies to be just right using the power amplifiers I had on hand. If there's anything amiss with the M3s' upper frequency presentation, it is well above my own upper frequency limits.
The most problematic aspect of the Spatial M3 Turbo S is matching the loudspeaker to the right amplifier. Because it is 94-dB efficient, the M3 does not need a high-powered amplifier, but it does need a low-noise one. My 17-year-old Pass X-150.3 power amplifier, which mated perfectly with my 90-dB efficient Dunlavy SC-VI loudspeakers, proved to be too noisy to use with the 94-dB efficient M3 loudspeakers, as did my stock Dyna Stereo 70, Adcom GFA-535II and GFA-545. The April Music Eximus S-1 and Bel Canto 600M mono-block amplifiers were both good matches for the M3, as will be any amplifier that has above average signal-to-noise specifications.
Like any high-quality loudspeaker, the Spatial M3 requires a proper setup to approach it full sonic potential. Placing the M3s too close to a front or side wall or placing them in a non-symmetrical room where side walls are quite different in distance or physical makeup will have a negative effect on the speaker's ability to image optimally and generate an evenly distributed frequency response. However, these issues will be less severe with the M3 than any conventional loudspeaker due to the M3's controlled dispersion pattern.
Comparison and Competition
While Emerald Physics offers similar designs, almost all of the Emerald Physics designs are either more expensive (such as the excellent CS 4.3) or have a simpler driver array (such as the EP-X). Also several of the Emerald Physics designs require four channels of amplification, which necessitates the use (and cost) of additional power amplifiers. Most Emerald Physics designs also employ a digital crossover/EQ to smooth out the compression driver's frequency response, which is not needed on the Spatial M3 because it has a custom compression driver instead of the more standard unit that was used with the CS 4.3.
While there are a number of conventional loudspeakers with limited dispersion patterns, only horn-loaded designs can have a fully controlled dispersion pattern like the M3. However, most horn designs (especially older ones) are large arrays that require a good deal of space around them. Some horn loudspeakers are so large that they can only work in a fairly large room, but the M3s can be used in a modestly sized room because of their unique design characteristics.
As everyone knows, it is virtually impossible to come up with something completely new under the sun, but a clever speaker designer can come up with a combination of ideas that have never been used together before. That is exactly what Clayton Shaw has achieved with the Spatial M3 Turbo S. It is a horn-type loudspeaker that employs a compression driver to achieve a controlled dispersion that is an identical 80-degree angle throughout its entire frequency range. Except for the offerings from Emerald Physics, no other loudspeakers can offer similar performance in terms of efficiency and controlled dispersion.
For $2,600 you can find loudspeakers that will play loudly, or loudspeakers that will image well, or loudspeakers with low amounts of midrange coloration, or loudspeakers with good bass extension--but it is rare to find a loudspeaker at this price that does all these things exceptionally well. The Spatial M3 Turbo S achieves exactly that. This "nearly" unique design offers all the advantages of a horn-based design without the problems of placement or excessive sonic personality. In many rooms, especially those with bass issues, the Spatial M3 Turbo Ss can perform at a level that is impossible to achieve from a more conventional design without DSP or room treatments. In conclusion, if you're in the market for new loudspeakers, you owe it to yourself to consider the Spatial M3 Turbo S. It can do it all.
• Check out our Floorstanding and Audiophile Loudspeakers category page to read similar reviews.
• Visit the Spatial Audio website for more product information.