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Feastrex D5e Driver Review

Phillip Holmes speaks of a realm of near-perfect, full-range response in the Feastrex D5e Field Coil All Permendur Driver

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Feastrex D5e Field Coil All Permendur Driver

*Editor’s Note:

Dagogo always provides an edited draft of articles to the importers for fact-checking before publishing.

We received the following information from Joe Cohen of Lotus Group USA on 2/23/09: “Phillip Holmes did not hear the All Permandur Field Coil, but the Type II in which the plate and pole piece are Permandur but the yoke is not (pure iron).”

Many of us have been down the road of modifications and upgrades where the improvement is hard to pin down. You know it’s there, but it’s difficult to quantify. Words like organic or palpable are used. Most upgrades and mods are incremental refinements looking for gains of a percent or two. However, there are times when the change is so dramatic, and the results make music so much more realistic, it makes everything else seem slightly un-real in comparison. I have to say that the Feastrex D5e field coil driver, in the brief time I was exposed to it, made an indelible impression on me. It’s like my first steak at a four-star steak house or my first 15-year-old single malt scotch. I knew it was special in the first few seconds that my feeble mind started to interpret the little electrical signals it was receiving.

Joe Cohen, the U.S. importer of Feastrex, has the following comment in regards to the application of Feastrex D5e in the American MaxxHorn Lumination design:

“The D5e field coil driver that MaxxHorn designer/engineer Johann van Zyl used was the standard aluminum framed D5e Type II. There are three types of D5e field coil: The D5e Type I where the plate, pole piece and yoke are all made from pure iron. The D5e Type II where the plate and pole piece are Permendur and the yoke is pure iron, and the D5e Type III where the plate, pole piece and yoke are all made from Permendur. Permendur is an alloy consisting of 49% pure iron, 49% cobalt and 2% Vanadium. It has high permeability at high flux densities with a very high saturation point.”

Having reviewed the Monster Alnico 5” equipped MaxxHorn Luminations, I had a good handle on what it sounded like. The two 5” models are cut from the same cloth (cone, surround and some other parts are pretty much identical). There is more similarity than difference when comparing the two drivers. However, the field coil technology improved the performance more than I could have imagined. It put to rest the Doubting Thomas in me that said: “that field coil nonsense is just a bunch of tweaky audiophile lunacy”. I should’ve known better than to go in with prejudices.

I got to hear the Monster Alnico and the field coil drivers side by side, which was instructive. Hearing the two versions of the Luminations side-by-side put the differences into contrast. Besides a direct comparison with

the Monster Alnico, there was some experimentation with the power supply, which has variable voltage (three voltage settings if I remember correctly).

The first difference, and the one that is most beneficial, was a better high frequency response. Don’t ask me how or why, but the field coil goes higher. If I had to put a value on it, I’d say it’s at least ¾ octave better; maybe an octave, but I don’t make measurements. That doesn’t sound like much, but a five-inch full-range driver needs every bit of high frequency extension it can get (and bass for that matter). The breath of life is in the highs and the way the highs interact with the midrange. Thankfully, with a full range driver, there’s no crossover to muck up the relationship.

That means that you might give up an octave on top for more truthfulness up to that high frequency roll-off; quality over quantity, you could say. If you read my review of the Luminations with the Monster Alnico, you know I slightly criticized the driver for having a wee bit of golden quality, similar to “classic hi-fi”, but without the “classic distortion”. The extra extension nearly eliminated the golden quality, elevating the high frequency performance very close to that of a good electrostatic speaker. There is still a slight rolling off above, but the D5e is much closer to the ideal full-range dynamic driver. At this rarefied territory of near-perfect full-range response, you can make up for the slight roll-off with associated cables, tube rolling, source selection and very precise speaker positioning.

An area that showed improvement, and something I would never have expected, was an improvement in transparency and detail in the midrange. I thought the Monster Alnico was as good as it was going to get in that regard, maybe only equaled by electrostatics. I would guess it’s the greater flux density in the gap which makes the driver respond better. I don’t know. I’m not a speaker expert. The field coil must have greater strength compared to the Alnico. We did experiment with the voltage to the electromagnet and the highest voltage improved every aspect of performance, but especially detail. As the voltage decreased, the sound retreated to characteristics more similar to the Monster Alnico, with a decidedly more laid back, golden, lush sound. The highest voltage seemed to flesh out the detail significantly better.

I can report that all MaxxHorn speakers now have improved bass. When we compared the Monster Alnico with the D5e, both versions had better bass extension than the previous MaxxHorns I had heard. The designer, Johan van Zyl, has slightly changed the loading of the driver, something he showed me that I cannot explain. It amounts to a slight modification of the flare of the horn and how the driver is loaded. The results are better bass from any driver you use in the enclosure. Weight and extension improved. Damping was better with no noticeable overhang. A disappearance of slight “chestiness” that I had previously heard on a few male vocal recordings.

When comparing the D5e to the Monster Alnico, bass had better weight, depth and definition with the D5e. It was an improvement in all areas. With the modified (actually, just a slight tweak that can be performed on any previously built cabinet) cabinets, the D5e is nearly able to accomplish a bass miracle from a 5” driver. When carefully positioned in the room, lows are very satisfying. I think most, if not all, of the ported boxes I’ve owned could not go as low as the Luminations with either of the Feastrex drivers. Also, ported speakers positively do not have the definition or speed that these horns have. When comparing to my Maggies, the low-end cutoff was nearly the same, but the MaxxHorns had better dynamics and less, much less, power compression.

There is another observation about the variable voltage settings. The speakers were more sensitive at the highest voltage: I would guess 2-3dB difference from lowest setting to high. That seems obvious enough. More voltage means a more powerful electromagnet. I was left wondering what the maximum allowable voltage is. I could find no information on the web with the outside limits of supply voltage. Perhaps it’s out there and I didn’t stumble across it. I would assume that Feastrex has used very high quality wire that is probably capable of handling greater voltage. However, not knowing what the breakdown voltage is, and seeing as these drivers are supremely expensive, I’d just stick with the prescribed voltages—if it were me. On the other hand, if any of you readers are rich, willing to burn through money, and want to find out for the rest of us, please crank up the field coil voltage till they catch fire and let us know what voltage that is. A safety margin would be to take 20% off of that. I’m only half joking here.

Again, another prejudice has been struck down (for me).

Field coils aren’t hooey. Cost and complexity are the reasons they disappeared for 70 years. Permanent magnets are always cheaper than a well-built field coil driver and associated supply. By the way, the same thing can be said about the elimination of interstage transformers in favor of capacitors. There are other field coil options out there, including large woofers and compression HF drivers. Anyone care for a three-way field coil system with a D5e covering the important octaves?

We are slowly rediscovering another lost art and Feastrex seems to be at the vanguard. How about a line array of the D5e’s with a MaxxHorn subwoofer utilizing BASSMAXX Horn Technology? Still, these are very expensive. For many who are interested in full-range performance on this level, they might not be able to find the money. The good news is that, just like NASA technology trickling down to improve our mundane lives (remember Tang and Velcro?), there is a new entry-level field coil from Feastrex. Perhaps it has most of its big brother’s magic. I spoke with Bob Spence about the driver and he indicated that they will be offering it as an option. Till I hear it, though, consider the D5e without peer. Nothing approaches what this Feastrex can do, especially in a properly designed cabinet like the MaxxHorn.

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