Us Recap The OB4.5 Monitor Review
Eric Alexander is obviously aware of the shortcomings of his design. For those who wish a more splendid treble he offers a very modestly priced tweeter with a minimal crossover. And for those who can't live without a powerful bass he has built upon his earlier acclaimed success with subwoofers and out-performed himself with a new patent-pending design, the S12. The custom paint jobs and optional veneers he offers for both the OB4.5 and S12 should quell the apprehension of the design conscious.
The two drivers are wired so they both push and both pull together. There is no compression behind the front driver because the rear driver is sucking the air from behind. The rear driver compresses the air behind it in the acoustic suspension box. Likewise, there is no compression from the rear driver when it pushes forward, because the air in front of it is moving into the void created by the forward moving front driver. Thus, the only effective compression recreating the sound wave comes from the front surface of the front driver. The S12 is essentially an open baffle monopole subwoofer, a patent pending design. The back wave of the front driver is nullified and the music comes from the front of the open baffle. Placing my head behind the front baffle of the speaker I experience a relative musical void, hearing only what is coming around the edge of the front baffle. The advantage of this design is the front driver works with greater transient speed and accuracy without having to deal with the compression on the back wave. The upper end of the subwoofer's range is intentionally rolled off at 24dB/octave.
This tandem arrangement in the subwoofer is not unlike the use of the second full range driver in the OB4.5. In the monitor, the upward facing driver mounted in the cabinet behind the open baffle essentially performs a similar function, primarily in the bass. A ported enclosure is used to reinforce the bass with this particular Fostex driver. Because the drivers are at right angles to each other, the mid and high frequencies are permitted to continue rearward in typical dipole fashion, thereby creating a sense of spaciousness as I mentioned in the earlier review.
On small group acoustical music the S12 brings a more realistic sense of space with added room tone. The importance of this was demonstrated at the Montreal show this year when Graeme Humphrey from Coup de Foudre demonstrated the new Wilson Audio subwoofer, Thor's Hammer, in conjunction with the Maxx III. The effect is primarily qualitative. Switching Thor's Hammer in and out of the system showed how a good subwoofer improved the quality of the midrange and brought a more real sense of being there to the music. The Maxx III certainly didn't need help in producing the fundamental musical tones, but the addition of the Hammer reproduced the room tone of the recording and brought the experience closer to that of a live performance in a room that was several times the volume of my listening room.
Performing this same exercise with the S12 and the OB4.5 I experienced the same result to a somewhat lesser degree with the additional benefit of a tonal shift of the epicenter of the music to a point lower in the midrange. In this case, the S12 was contributing additional fundamentals that the monitors could not effectively produce. The music had more weight, better tonal balance and even the treble seemed better resolved — go figure! But one shortcoming became apparent, though not particularly annoying. While the soundscape of the upper bass on up was beautifully portrayed and three-dimensional, the mid and lower bass seemed more one-dimensional. Not "one note", mind you — it was definitely very tuneful, but the music lacked the colorful life-like feeling coming from the monitors. If it was a TV set, I would have said the chroma had been turned down. With great loudspeakers such as the Coincidents that I've reviewed in the past year, I wrote that I could "taste the skins" of the drums. That wasn't happening with the S12. The notes were fast and focused, and they integrated perfectly with the monitors, but something was missing. Was it the fact that the bass from the left and right channels were summed in this monaural subwoofer? I shot an email to Eric and made an unreasonable request for a second S12. He came back with an apology for not having sent two to begin with.
Like the OB4.5 reviewed previously, the subwoofer exhibited outstanding transparency, tonality, transient speed and absence of box colorations. This is a bit unnerving at first and takes some getting used to. There is no warm, fuzzy feeling here. Nor is it cold or clinical. Such neutrality merely conveys what's on the source. My LPs took a jump up to the kind of focus, transparency and bass response that I was previously experiencing with CDs. As a side bonus, adding the deeper bass seemed to minimize my awareness of the clicks, pops and surface noise previously enjoyed. Possibly this was because the acoustic center of the now full-range loudspeaker had been lowered to the acoustic center of live music — further below the frequency of the clicks and pops. My CDs, in similar fashion, were reincarnated a generation closer to the holy master tape. Keep in mind we are talking about the contributions of a frequency range of about 60 Hz, from 20 Hz to 80 Hz, while the monitors cover a range of thousands of Hz. The point here is that the perceived contribution was substantial and continuous with the monitors. I simply enjoyed the music with the subwoofers a whole lot more than with just the monitors. In a blind test, I would have guessed they cost thousands more than they do. Bass fans can rejoice; the adjustable volume on the back allows you to choose the tonal balance that pleases you (within reason, of course). I achieved what I thought was a relatively flat response, relative to the midrange, without using any measurements. When I switched the bass out, the effect was subtle for most music, affecting the sense of ambient space in the recording. Yet the few instruments producing bass fundamentals were more prominent by virtue of the transparency and focus of the open baffle design and the tightness afforded by the BASH amplifier. Following bass lines in the music was simply a matter of wanting to. More frequently my attention was captured by the interplay of the instruments, but most of the time I was mesmerized by the gestalt of the music.
One problem became evident when I played "Master Tallis's Testament" from Pipes Rhode Island. The subterranean organ notes broke up the little Fostex driver in the monitors while the S12 handled them with aplomb. Turning off the monitors and playing only the subs showed me that the subs were doing just fine.
Then, out of a sense of obligation, not evil, I cranked up the volume. The subs playing alone broke up when playing back the deepest organ notes at 100dB in my large listening room. This probably correlates to the affordable drivers, not the design. Those organ notes were probably below the free air resonance of drivers. With more normal listening material, including rock and classical, it was rare to experience any break up of the monitors and never was the rule with the subwoofers at listening levels peaking at 92dB at the listening position.
Combining the two S12 subwoofers with my full-range Kharma loudspeakers was also a revelation that was mostly positive. The additional fullness in the mid and lower bass was especially welcomed. It was also evident that the mid-bass of the S12 was more clearly focused than that of the Kharma 3.2c even though the driver in the ported Kharma was more "high-tech". In fact, the bass from the S12 was more highly focused than the rest of the music which had a very pleasing, but warmer presentation. Of course, part of the reason is that I was driving the Kharmas with the relatively low powered Manley Mahi monoblocks in triode mode, albeit somewhat tweaked for considerably better focus than stock. The other part of the reason was the 300 watt BASH digital amplifier in the S12 that undoubtedly had a better grip on the driver than a Mahi could ever hope to muster in the bass region. I crossed over at about 80 Hz to give the mid-bass a little stronger presentation. The more highly focused signal from the S12 seemed to mask the warmer sounding low frequency output of the Kharma without apparent problem. Remember, both the S12 and the Kharma were being driven full-range, although the S12 is rolled off sharply at the top end.
I adjusted the crossover down to 50 Hz and pumped the volume up to maximum. The measurements of this adjustment are what you see here with the difference between the monitors + subs and the monitors alone shaded in red to give you an idea of the energy contributed by the subwoofer. More than producing a better looking curve at the low end, minimizing the overlap of the sub and monitor cleaned up the mid-bass, improving the focus even further in that region. Increasing the volume gave me a stronger bass response than to what I was accustomed. The stronger bass sometimes buried the vocals in the midrange deeper into the music. For several late night/early morning hours I revisited key recordings, reveling in the qualitative improvements and getting accustomed to the stronger deep bass. The fine tuning made a great sounding musical presentation even more outstanding. The hump in the upper bass region is a room node which doesn't bother me since it has been there with every piece of gear I've reviewed. I'd probably think something was dreadfully wrong if I installed a room correctional device. The important thing here is the bass below 70 Hz was dramatically improved.
While the subwoofer by itself is relatively innocuous, it didn't take me long to come up with the idea of using a sock around the pillars (ala Vandersteen and Von Schweikert) to conceal the back side of the driver on the open baffle. Eric liked this idea and it may be implemented in the future. If not, a quick trip to a fabric store and a little sweet talk with a seamstress should get the job done. Pick your favorite color, pattern or texture; everything goes with black.
After living with this gear for several months, I pretty much ignored its presence. It will not contribute to the elegance of your room unless you paint it up like an object d'art, but that's not what it's all about. The OB4.5 and S12 are cutting edge technology and Job 1 for Eric Alexander is to get it out there and show the world that it works. Dressed in black, it's all about the music. And it that form it is one of the very highest value full range loudspeakers I've ever heard.
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