Most of you are probably too young to remember the Spendor BC-1 loudspeaker, a British design that garnered rave reviews in the late 1970s for its musical naturalness and imaging prowess. On cursory examination it seemed to be an ordinary three-way design, but, more to the point, it could best be characterized as a two-way design augmented by a super-tweeter. My initial take on the BC-1 was that the super-tweeter was nothing more than a token driver, a “hood ornament” whose sole purpose was to fill in the extreme treble. Only years later did I come to realize its importance in enhancing midrange transparency. At least conceptually, the M1 from ENIGMAcoustics reminds me of the BC-1, being a compact two-way stand-mounted speaker that is specifically designed to partner ENIGMAcoustics’ Sopranino super-tweeter in the extreme treble. The Sopranino (see review, Issue 235) is a self-biased electret tweeter, which in this application, sits on top of the M1. A cable is provided to connect it to the M1’s speaker terminals. Of course, the M1 easily trumps the venerable BC-1 when it comes to driver technology.
Let’s start with the woofer, a 7-inch custom design that features a polypropylene cone, a 2-inch voice coil, a highly compliant rubber surround, and an exceptionally strong and precise magnetic motor system. Quality control is said to be tight, with each batch of woofers being within 1dB of a standard curve. However, the key to this speaker’s sonic excellence is the tweeter. It’s a 34mm silk dome that was painstakingly developed utilizing considerable modeling, simulations, and much trial-and-error to achieve high efficiency (95dB) and usable bandwidth from 1kHz to 20kHz. The crossover frequency is a remarkable 1.1kHz, whereas the typical crossover frequency for a 1-inch dome is around 3kHz. This is a big deal in that it allows the M1’s woofer and tweeter to integrate far more smoothly than the average two-way is capable of and significantly improves the power response in the upper midrange. Push a 7-inch woofer to 3kHz and it starts to beam like a flashlight, meaning that its off-axis output drops dramatically. Experience has shown that a uniform power response in the midrange correlates well with perceived tonal-balance accuracy at the listening seat. It should also be emphasized that having what is essentially a low-mass point source of sound reproduce the core of the midrange and treble range yields an inherently more cohesive and focused presentation than is possible with two dissimilar drivers overlapping at 3kHz. I’ll have much more to say about these performance aspects a bit later.
The tweeter is protected by a third-order, electrical high-pass network, which is said to have been the most time-consuming design task, since the tweeter’s free-air resonance frequency is at 750Hz, less than an octave removed from the crossover frequency. It incorporates a 10dB resistive attenuation network to match the woofer’s sensitivity. The horn-flared tweeter faceplate compensates for a slight frequency dip in the 2–3kHz range, alleviating the need for a complex correction network. The woofer’s low-pass network is second-order, making the overall crossover an asymmetric type in that it combines second- and third-order networks. The advantage of such a network is that it provides a measure of time delay that is useful for phasing the tweeter and woofer in the crossover region. It is clear that the M1 is “a labor of love,” and this is reflected in the high-quality passive components used throughout: Mundorf EVO and EVO oil capacitors, Solen MKP capacitors, Cardas internal wiring, and WBT binding posts.
While in theory it’s possible to squeeze decent sound out of cheap drivers, my long held view has been that truly great speakers are built on the shoulders of superb drivers. The M1 reaps the benefits of in-depth engineering in the service of an outstanding driver complement. One of the quantitative benefits of this convergence is an exceptionally uniform on- axis frequency response as measured on the tweeter axis. Not only was the measured response exceedingly flat nearfield, but it also continued to behave extremely well when I moved the microphone to the listening seat. That translated directly into exceptional tonal-color fidelity. In-room bass extension measured flat to 40Hz nearfield and reached the mid 30s at my listening seat—superb performance from what is after all a rather small bass-reflex design.
The user manual offers detailed and generally useful guidance on how to set up both the main speakers as well as the Sopranino. The recommendation to align the Sopranino toe-in angle with that of the main speaker makes perfect sense, as does the advice to experiment with depth of placement relative to the front edge of the M1. There is a series of grid lines marked on the top of the main speaker cabinet, spaced about one-quarter inch apart, to aid in front-to-back positioning. Expect the treble balance to shift somewhat as you move the super-tweeter even a single notch along the grid lines, due to acoustic interference in the upper treble range between the silk dome (which isn’t electrically rolled off) and the super-tweeter. The manual pictures the Sopranino at its default position, which appears to be with the front edge of the enclosure’s base even with the third grid line. After experimenting with the Sopranino positioned at the first, second, and third grid lines, I settled on the third grid line, which in conjunction with a level setting of -3dB and a crossover frequency of 12kHz, not only measured best but also yielded the most natural overall balance. My ears tell me that the suggested default settings for gain and crossover frequency of 0dB and 10kHz sound too bright. There is a clear and present danger in trying to make the super-tweeter do too much. At some point, the balance crosses the line between the real and surreal. For me a bright balance is a serious matter, almost on par with a rift in the space-time continuum. I’m basically guilty of disliking a rising treble response and gravitate toward a mid-hall presentation. If your priorities are aligned with capturing the balance of the real thing, don’t be seduced by the dark side of the Force, and do stick with my recommended gain and crossover-frequency settings. Once you’ve adopted these settings, it may be perfectly fine to move the Sopranino forward to the first grid line. Doing so produces a more prominent treble impression, which may well compensate for treble roll-off induced by power amps with significant internal source impedance (i.e., low damping factor).
Impedance measurements indicate a box tuning of 36Hz. As is usually the case, the impedance magnitude is far from uniform. Significant features are a peak of about 50 ohms at the 1.1kHz crossover frequency and impedance minima of 4 ohms in the midbass and 2 ohms circa 15kHz. The impedance dip in the upper treble proved problematic for tube amplifiers, especially those with a source impedance over 2 ohms. In fact, every tube amp I tried produced some measure of treble roll-off. The best coupling for the M1 turned out to be the Lamm Audio M1.2 Reference monoblocks. Based on my experience, I’m convinced that the M1 would be happiest when partnered by a high-quality solid-state amplifier.
My first listen to an early version of the M1 was during a Consumer Electronics Show a couple of years ago. I was in for a big sonic surprise. Here was a small stand-mounted speaker, which I fully expected to exhibit a lack of testicular fortitude, and yet against all odds, it managed to portray the music’s foundation with believable authority. Small speakers are not supposed to do that, and none that I’ve auditioned in the past have done it as well as the M1, which explains my past lack of enthusiasm for this “imaging without guts” speaker genre. For me, a primary ingredient in the enjoyment of music reproduction is a realistic tonal balance, and in particular, a lower midrange weight that does justice to the orchestra’s power range. In this, the M1 succeeded reasonably well, to the extent that I was able to embrace its version of symphonic music. Bass lines were tight and free from the sonic muddle that accompanies a resonant enclosure. The M1’s rigid enclosure stands in stark contrast to the thin-walled British monitor class, which adds false warmth to the upper bass and lower midrange in the hope that this coloration, or should I say artificial boom, will somehow be consonant with the music. The M1 is serious about bass accuracy.