Unique materials & artisan technologies


1. Washi
2. Handcrafting Methods
3. Leather surrounds
4. Voice coil technology
5. Phase plugs
6. Machining and metallurgy
7. Rear affixing of the drivers
8. Annealing
9. Pure iron
10. Permendur
11. Naturflux
12. “Monster Alnico”
13. Field coil magnetic circuits
14. Field coil power supply unit (PSU)

Washi: Washi is one of the most famous traditional Japanese artisan handcrafts. There are many varieties of washi, but the incredibly strong type used in the main cones of Feastrex drivers, known as hosho-shi (pronounced like English “hoe-show-she”), is made from the middle bark of the mulberry tree (kozo in Japanese). Surprisingly, the trees are not killed during the bark harvesting process. Feastrex’s hoshoshi, representing the absolute ultimate fruition of the art of this particular paper type, is produced through an amazing process about which you can read more here: http://www.washiya.com/shop/iwanohousho/kodawarienglish.html

Handcrafting methods: The processes that go into handcrafting Feastrex drivers could easily fill an entire book. The full complexity and importance of every detail of every step of the process is appreciated only by the brain of the builder, Mr. Teramoto, but suffice it to say that despite the extensive hand building techniques, absolutely nothing is left to chance. Every aspect of construction has been thoroughly thought out and examined from multiple angles. Construction requires an incredible amount of focus and dexterity, but even more important is discipline. Most of our tools and jigs have been custom CNC made for us out of special materials in order to assure the absolute maximum product consistency. Because of this fanatical attention to detail, we are confident that no mass market speakers can approach our level of product quality assurance and consistency.

Leather surrounds: Our leather surrounds are made from hand-selected, cut and glued pieces of a soft, lightweight leather. The cone assemblies are supported at one extreme by these surrounds, and at the other extreme by our spiders (dampers) which are also made of a completely natural material (cotton). If synthetic materials were used instead for these roles, the sound character of the drivers would change, understandably for the worse. From the perspective of the resulting tone of our drivers, we think there is much to be said for our approach of building almost entirely from natural materials. Along with our washi paper, (which is extremely stable and could remain serviceable for centuries), these surrounds will likely outlive the original owner of the drivers. We personally own examples of speakers with leather surrounds that date back to 1929 that are still fully, beautifully functional (even though they did not have nearly as high a quality of leather as Feastrex drivers). The hand-formed leather surrounds are an incredibly important component of our driver’s uniquely organic and effortless sound. Also, we feel that leather is likely the MOST durable surround material possible in order to assure driver longevity.

Voice coil technology: Our voice coil formers are made from a special type of strong, stable washi and edge-wise wound with (nominally) 16-ohm ribbon wire for maximum efficiency.

Phase plugs: Our phase plugs are molded acrylic for the Naturflux models, and gold-plated bronze for the NF5ex, “Monster Alnico,” and Type I field coil drivers. For the Type II and Type III field coil units, the gold-plated bronze plugs are finished with urushi lacquer. Any Feastrex driver’s phase plugs can be optionally replaced with a different type, at the time of ordering, or purchased later.

Machining and metallurgy: Machining and metallurgy are accomplished by top-level Japanese manufacturers who are themselves audiophiles and lovers of Feastrex drivers. The quality of the metals found in our magnetic circuits, from S10 iron to pure iron, to Permendur is second to none. We go directly to the source for these metals, thus achieving maximum cost efficiency under the circumstances. The shop overseeing our machining takes pride in a level of workmanship that could pass muster for the most critical applications anywhere in the world. Our magnetic circuit parts are machined to such precise, tight tolerances that if they were any tighter, it would be almost impossible to assemble them. (As it is, assembling even a small batch of motors can be exhausting for the builder.) This attention to detail and precise construction within the magnetic circuit yields definite advantages to the sound: the more tightly these parts fit together, the better the driver will perform. As the tolerances of the piston and valve train within a formula one engine must be kept incredibly tight in order to avoid air leakages, so a magnetic circuit’s tightness keeps the precious flux from leaking at the joints.

Rear affixing of the drivers: While titanium screws securely hold the driver frame to the magnetic circuit, the entire driver can be affixed from the behind the motor via an M8 bolt that goes into a corresponding bolt hole in the center of the back side of the motor. This can be used to help decouple the driver from the front baffle. (Conventional front mounting via six bolt holes in the driver’s front mounting flange is also possible.)

S10 iron: Our Naturflux and NF5ex drivers’ yokes are made using S10 iron, which is close to pure Iron. It has excellent magnetic permeability and results in a very natural, relaxed sounding driver. Although S10 is Feastrex’s “entry-level” material, we are confident that our forged and CNC machined S10 iron may be rightly considered superior to the magnetic yoke materials of almost any other manufacturer’s full-range drivers.

Annealing: Proper annealing is absolutely essential for the metals used in a transducer’s magnetic circuit in order to achieve the best possible performance. Each metal must be heated and then cooled under conditions that are precisely controlled with regard to the time and temperature curve, and ambient atmosphere. Hydrogen atmosphere annealing is the process by which a material’s magnetic properties can be enhanced. This process reaches temperatures of up to 1400 degrees C and takes many hours to complete.

Pure iron: The carefully annealed pure electrolytic iron in the yokes of our Type I field coil and “Monster Alnico” magnetic circuits is responsible for an even more detailed, natural aspect to the driver’s sound. The background is even quieter (“blacker”) and the sonic images are more vivid, lush and intense -- a very pleasing sound.

Permendur: Our Permendur is truly an ultimate high-permeability soft magnetic material and results in a completely unparalleled level of detail and naturalness to Feastrex’s sound. Although incredibly expensive and notoriously difficult to work with, because of its high magnetic permeability, Permendur is easily the best-sounding material for building a magnetic circuit. This is the stuff that audiophile legends are made of. If one refuses to compromise in one’s pursuit of the best, one turns to Permendur. The sonic difference that Permendur brings is difficult to put into words, but it is not at all subtle. It must be heard to be fully appreciated. One hearing is worth a thousand words and also an absence of words simultaneously.

Naturflux: Our patent-pending Naturflux magnetic circuit is a genuine innovation in magnetic circuit technology and the drivers building on this technology represent an incredible value in the audio world. Asking magnetic flux to negotiate the sharp, 90-degree bends in a conventional magnetic circuit is like asking water to flow around a sharp right-angle curve. It can be done, but it’s not happy doing so, and inefficiencies result. Sharp bends affect magnetic flux and water pipes similarly: resistance increases with pressure and as a result flow volume falls off. (In the case of water pipes, the right angle pipe will actually get hot under a high enough flow rate). Where previous designs fought against the natural behavior of magnetic flux, the Naturflux magnetic circuit accommodates flux behavior and uses it more effectively. The Naturflux design demonstrates the importance of voice coil gap flux stability and strength in high fidelity sound reproduction. Our Naturflux drivers are immediately recognizable by their rounded yokes, but even our non-Naturflux field coil drivers incorporate the same concepts to a lesser degree, and definitely benefit as a result. Our non-Naturflux drivers compensate for their deviation from the Naturflux “ideal” through sheer massiveness of their magnetic circuits and the use of more expensive materials.

“Monster Alnico”: To our knowledge, our “Monster Alnico” motors are the most massive magnetic circuits ever produced in their respective driver sizes. There is much to be said for the sheer brute force approach of massiveness when designing a full-range driver’s magnetic circuit. Thanks to that and their use of Permendur pole pieces, and partial permendur top plates these drivers have a sonic character that is simply scrumptious and pleasing to no end.


Field coil magnetic circuits: Our field coil magnetic circuits can be divided into two different categories. One is the Naturflux field coil magnetic circuit, as found in the NF5ex. It uses conventional round wire in the exciter coil and a spherical S10 iron yoke. The bass from this circuit is incredibly powerful, with very natural dynamics and incredible microtonal resolution. The Type I/II/III field coil drivers all use patented square wire in their exciter coils for 99% packing efficiency. This results is a more efficient, powerful, and cooler-running motor and drivers that perform with incredible effortlessness. The Type I motor’s yoke, pole piece and top plate are made of entirely of pure iron. The Type II driver also has a pure iron yoke, but the pole piece and top plate are made of Permendur. In the Type III field coil motor, the yoke, pole piece and top plate are made of entirely of Permendur. These field coil drivers have astonishingly good sonic performance -- massive, beautifully detailed, supremely controlled and with limitless energy.

Field coil power supply unit (PSU): Our field coil drivers all require a separate power supply. After extensive research on power supplies of every imaginable type, we are confident that our power supplies realize a level of performance that can not be easily surpassed. All the parts are of the best quality, including superb R-core transformers specially wound for us by Japan’s leading manufacturer of this type of transformer. Particularly noteworthy is our use of what we believe to be (by a large margin) the world’s most advanced solid state rectification diodes. Our PSUs were developed with the special assistance of the creator of these diodes, Mr. Saburo Degawa. For more information, please refer to this link:


Feastrex.com © 2008 All rights reserved. Feastrex.com Japan: contact Haruhiko Teramoto. IBI Co., Ltd. Aesthetics Development Division. 7841 Anayamacho, Nirasaki, Yamanashi 407-0263 Japan. Tel +81551227221. "Hal (at) feastrex (dot) com"