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My time with the $42,000/pr Feastrex D9e-II field-coil drivers was followed by a pair of another unique and even more massive eight-inch field-coil driver from the folks at Lowther America. These soon to be available drivers are functionally Lowther PM7s from the voice coil forward. They use four-bolt frames available on Lowther models from the PM7a down to make a stable connection with a very heavy eight-inch long field-coil housing. Mr. Dave Slagle winds these field-coil motors with ten pounds of square copper wire.
The specifications for these weren't available yet when I received the prototypes. I'll surmise that their frequency response pretty much follows that of the PM7a. However, the efficiency of these drivers is dependant to a degree on the voltage and current supply settings of their electromagnet motors.
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As such, the relative frequency response character will be tied to that of the voltage and current fed to the field coils via their power supplies. It's not that different from having a magnet-strength attenuator at your finger tips.
But if that's all there was to it, shouldn’t they simply sound like one of the bigger or smaller Lowther already available as one increased or decreased the supply voltage and current to match the field strength of the fixed motors? That would seem a great and obvious question. First let me describe the system I used to evaluate these rather robust drivers. I'd been awaiting the arrival of a FirstWatt J2 transistor amplifier to evaluate the 92dB efficient Feastrex D9e-II field-coil units. When UPS decided that this J2 needed a long tour across the country, I was relegated to using my 2wpc Yamamoto A08-S 45-based SET amplifier on the Feastrex. All was peaches however when this turned out to be a very nice pairing.
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Fortunately a replacement J2 arrived in time for the Lowther field-coil assessment. Hence I would evaluate them with a First Watt J2 amplifier, the Yamamoto A08-S, a vintage Fisher SA-16 15wpc EL84 stereo amp for baffle woofers, an S&B equipped Bent Audio transformer-based passive preamp with remote volume, MHDT Havana DAC, Ayre QB-9 USB DAC, Sony XA777ES for SACDs only, DIY fine silver interconnects throughout, Audience AU24 and AU24E speaker cables, Locus Design Nucleus USB cable from PC to either DAC, Western Digital 1TB external USB hard drive, Mana four-tier amp stand, PS Audio P300 power regenerator for the DACs only and two Mastech HY1803D DC-regulated power supplies for charging the field coils.
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Would these Lowther America field-coil drivers sound like other Lowthers? Nope. Did the field coils sound better then? In my opinion they should at least sound different from an otherwise identical driver since only the magnet type changed. It's a similar issue to Neodymium vs. Alnico. This time of course I knew the driver in its original form. I even had a pair of standard Lowther PM7a on hand. If I could approximate the field coil’s magnet strength to closely match that of my PM7 Alnico magnets, should they not sound mostly alike?
They did not. The Lowther field coils were again fitted at 31" inches high into my 24" x 41" baffles unfiltered but assisted by a pair of 12" Tone Tubby Alnico hemp-cone woofers 13" off the floor. The TTs were crossed over at 212Hz using a single toroidal 12MH inductor. All my OBs are further bass assisted by a pair of 10" corner-loaded powered subwoofers if needed. In this case I brought the subs in at around 70Hz.
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The Lowther America field coils immediately got my attention in a different way from previous field coil or other drivers. They sounded huge, as though I had two pairs of eight-inch drivers moving air instead of just one. They otherwise did not draw attention to themselves in the overt manner of the Feastrex D9e-II. The Feastrex's midrange delineation sounded as though life-sized marble replicas of vocalists and instruments had been placed in appropriate positions behind the baffles. In the critical midrange, the Lowther field coils produced similar weight, density and spacing as the Feastrex but not to the same degree of coherent clarity and not with quite their unforced level of presence.
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I was quite surprised by one area where the field-coil Lowthers caused a massive change over the PM7a Alnico version. As before with the Feastrex, I did most all of my listening on-axis. These Lowthers were so smooth and grain/bite-free that I found myself toeing them in until they pointed straight at me. This was a first with any Lowther. Anyone who has heard a Lowther sound its best knows the high level of lit-from-within presence and uncanny emotionally charged life they can produce. We also know that getting a good Lowther to this point requires due diligence and lots of patience. If we could aim them more directly at us, these inherent strengths would automatically increase were it not for the uncomfortable peakiness or bite. With the Lowther America field coils, there was no bite on axis either over the J2 or A08-S amplifiers.
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The high frequencies were so silky smooth that I initially thought they might actually be a bit rolled off even on axis. Yet all of the detail, speed and dynamics I am accustomed to with my bigger Lowther drivers was still there. Regardless, I still felt that a very good tweeter might further enhance performance in this range. But I am certainly not used to staring directly down the gullet of a Lowther whizzer without feeling the painful bite. I had the field coils charged to 15 volts and played at volumes I would generally find uncomfortable. As output increased, they remained smooth and retained that unique sense of moving far more air than any eight-inch driver ought to. The previously described very dense vocal and instrument image sizes remained true and appropriately scaled regardless of SPL.
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This iteration of the Lowther America eight-inch field coil widebander did not immediately reach out and grab my attention other than their immense aural scale, extreme smoothness and lack of bite and aggression when aiming straight at me. It wasn't until I reinstalled several other drivers and entire OB systems that I realized just how non-aggressive and comparatively neutral the Lowther field coils really were. Some of my previous favorites now sounded small by comparison as I subliminally feared. They also showed me how much more work was ahead to try and approach the novel neutrality of the Lowther America field-coil prototypes.
For now not much more should be said about this promising new driver because it's not quite in formal production yet. Word has it already that there will be another version incorporating a shorter motor housing to be easier to mount, perhaps physically similar to the big Feastrex D9e-II. I personally like the idea of the potential ultra simplicity of open baffles for evaluating almost all my fullrange drivers. I am ultra sensitive to the artificial enhancements derived from using front or back horns to enhance/modify the natural frequency-related volume balance of them. If you want more bass, add a folded or even huge straight horn. It can be fun but it’s not my favorite way of evaluating the native attributes of these transducers. Or perhaps add a largish and visually imposing front horn to raise the widebander's upper bass through lower midrange to compensate for the peaks in the upper midrange and high frequencies.
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Of course some of the newer (particularly field-coil) units don't require such artificial balancing enhancements. On the other hand, many fullrange drivers still might benefit. I personally have found that nearly all good fullrange drivers sound more natural in the simple open baffle format. Some OBs require diligent tweaking of alignment and toe in/out or the addition of on-baffle woofers and tweeters to sound their best. But in the critical presence region where all of my widebanders run unfiltered, they perform remarkable in simple open-baffle platforms and without the colorations derived from horns or cabinet-based designs. As you can tell, I am a fan of the simplest most natural-sounding format possible. What fits that requirement better than open baffles? Of course not even they are perfect.
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The $42,000 Feastrex D9e-II remains my reference for a state-of-the-art fullrange driver so far. However, the Lowther America field coil driver offers many of the Feastrex’s unique sonic benefits and even does some things the D9e-II does not. The introductory price for the Lowthers will be $5,000/pr. I still feel that the big Alnico PM5a and PM2MKII offer a stunning level of emotional enjoyment that's addictive. Also, my Altec 416 woofer with Supravox 215-2000 8" field coil, RAAL 140-15D tweeter and Duelund cast-copper tweeter crossover capacitor offers a very different perspective on open baffles. In the end, the OB format is something even the least inclined woodworker can enjoy experimenting with at home. |
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Publisher's comment: Though it should be obvious from the above that drivers referenced as fullranger or widebander here weren't actually evaluated in single-driver mode, the terms used interchangeably for lack of something better could still be misleading. This type of driver can approach fullrange or certainly wide bandwidth coverage but then relies on an enclosure of some sort. Most but not all such enclosures tend to be variations on rear horns though some are closer to ported alignments. Drivers like the French/Swiss Linæum-derivative Rubanoide, the German Physiks DDD bending-wave driver and the Manger also belong into the widebander category. Because they require augmentation with woofers at roughly 100Hz, they're traditionally never referenced as fullrangers.
This report shows how widebanders can be used on simple open baffles where they'll require augmentation in the bass.
To use widebanders as fullrangers will mandate an enclosure. More successful commercial single-driver iterations seem to suggest that such enclosures can get more complex to build and often require very significant prototyping to arrive at the most advantageous geometry. For most DIYers, the open-baffle concept championed by Chopper87 will thus seem to be the most attractive solution. In that context—and given the expense of such drivers—it's simply more accurate to call them widebanders rather than fullrangers. - Ed
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