Distilling the design goals and concepts for the oneZ led to a configuration featuring a mini monitor reflex enclosure of birch plywood loaded with a single full range driver. The architectural elements are thus enclosure type, driver selection, materials choice, and style. The following discussion examines each in turn..

the enclosure

An aesthetic of simplicity is the constant touchstone for the oneZ. Simplicity also extends to issues such as size and ease of construction. There is a place for large and complex enclosures in the audio arts, the oneZ is not that place. This aesthetic of simplicity ruled out the horn loaded and tuned quarter wave boxes so popular with those bleeding on the cutting edge of the single driver wide range speaker art. Vented vs. sealed box was never really an issue given the goal of high efficiency and the parameters of likely drivers. Thus a vented mini monitor was quickly selected as the most likely candidate. When the first oneZ prototype was fired up it was immediately obvious this configuration is capable of overachieving results. The task then became refining the details while extending the performance envelope.


A great deal of thought, design, prototyping, and redesign went into the details of the oneZ box design. Mechanical performance, manufacturability, structural integrity, ease of assembly, and style all formed an interactive system which drove the design through eight major revisions. We wanted a design the neophyte could assemble on a kitchen table yet looked like an experienced cabinet maker had lavished his skills on the joinery. Simple yet not too simple displaying the knowledge of just how critical a component sub-system the speaker box is now recognized to be.

A major design issue for high-end speakers is how to deal with unwanted vibration in the enclosure. Reaction forces from the driver as it works against the baffle surface and internal pressures cause vibration in all speaker boxes. It is now widely recognized that while these vibrations are relatively small the large surface area of the enclosure walls can result in audible coloration of the sound. The popular solution for this is to use thicker heavier walls. Taken to a sufficient extreme this can be effective, however there are costs. Costs in dollars for more material and then more dollars to ship the resulting weight. Costs in design as the thick walls expand exterior dimensions and/or reduce interior volume. And costs in tone quality when thick heavy construction is allowed to impart a thick leaden quality to the reproduction.

As the First Law of Thermodynamics informs us energy can not be created nor destroyed. Therefore damping materials work by converting mechanical energy (in this case vibrations in the speaker enclosure walls) into heat energy. During this process the walls still vibrate, when they are heavy this energy excites lower frequency resonance modes. Because of the high mass per unit of volume involved the enclosure tends to store energy and release it over a longer period of time. The lower frequency vibrations smeared out over time contribute to a thickening of the reproduced sound. As always in engineering there are alternative techniques available to address any issue. An alternative technique for enclosures is to make them stiff and light. The modern standard bearer for stiff and light hi-fi speaker enclosures was the Celestion SL600. With an enclosure made of aerospace structural honeycomb the SL600 epitomized the 'stiff & light' technique.

Basically the 'stiff & light' design technique accepts that in real world materials vibration is a fact of life and aims to manage the amplitude, frequency and resulting effects. When a structure is stiff and light its natural resonance modes will occur at higher frequencies compared to the same structure constructed from lossy heavy materials. The 'stiff & light' speaker enclosure takes advantage of the fact that on average music has most of its power at lower frequencies and less at middle to higher frequencies. Music instruments and styles have evolved this characteristic to match the lower sensitivity of human hearing at low frequencies. Thus the 'stiff & light' technique takes its enclosure out of harms way by placing its resonance modes higher in frequency where there is less energy to excite it. When the system is viewed in the time domain there are additional benefits to 'stiff & light'. Lighter structures store less energy and release it quicker compared to heavyweights. Given music's transient nature and resulting high peak to average power ratios the 'stiff & light' technique will result in less time smear compared to the longer ringing times of heavier enclosures. The oneZ design takes the 'stiff & light' technique and allies it with an energy trap (see materials section below) built into the front baffle. The energy trap attenuates the unwanted reaction forces generated by the driver before they can reach the rest of the enclosure. Remaining energy reflecting back into the baffle will be further attenuated by another trip through the energy trap before it reaches the driver/baffle interface. This increases  the mechanical signal to noise ratio of the driver mounting area of the baffle. A quieter more stable driver mount increases micro dynamics further revealing fine musical detail.

the driver

Selection criteria for the oneZ's driver called for balancing multiple criteria including musicality, electromechanical performance, reliability, efficiency, bandwidth, availability, and cost. Severest and most unusual among these is the desire to cover eight or nine octaves of the musical spectrum using a single driver with at least 90 dB/W/M efficiency. A crowd of contenders is thus immediately reduced to a field on one, Fostex. Worthy units from both the obscure and well know manufacturers in Europe, Japan, UK, USA, and Asia were ruled out on grounds of cost, availability, questionable reliability, and low efficiency. That Fostex would win out is hardly surprising given they bring the following long list of pluses:

• Large multi-national company.
• Professional audio division adds stability and cash resources.
• Located in Japan, the hotbed for both DIY audio and single driver full range speaker enthusiasts.
• Years of experience manufacturing wide range speaker drivers.
• The broadest and deepest range of high performance wide range speaker drivers of any manufacturer in the world.
  

The breath of Fostex's range of hi-fi full range speaker drivers became apparent as the driver for oneZ was selected. Flexibility and upgrade paths are desirable characteristics for any hi-fi component so it was great to discover not one but four Fostex drivers in the 100mm/4" class which will match the oneZ box.

1. FE107E - High performance shielded 80 Hz - 20 kHz 90 dB/W/M driver featuring ES banana pulp cone and new center cap design for extended high frequency response.
2. FE103E - Unshielded version of FE107E. Both FE103E and FE107E are very reasonability priced.
3. F120A - Ultra-fi Alnico magnet 65 Hz - 20 kHz 89 dB/W/M driver. Alnico for the final stop on the journey to musical bliss. Expensive.
   
4. FW108N - Wide range mid-woofer 55 Hz - 10 kHz 86 dB/W/M driver features hybrid pulp cone and 1.9mm Xmax for high output. Moderately expensive.
   

With multiple driver options oneZ becomes not just a hi-fi speaker but a system which can be configured in a variety of ways to better match individual needs and tastes. The configuration can also be upgraded or re-engineered as upstream components evolve over time. One can easily see three major configurations depending on which driver is loaded:

• FE103/7E - overachieving price/performance ratio with amazing direct coupled tracking of the input's every nuance.
  
• F120A - the ultimate mini monitor for the owner of an advanced triode amplifier as nothing brings out music's textures and emotional impact like Alnico.
  
• FW108N - high output bass/mid system for use with super tweeters and beefier amplifiers mixing a large measure of the coherence of a full range driver with the output capabilities of more mainstream large Xmax drivers.

The FE103/7E deserves further discussion. The biggest problems this driver has are:

1. its too inexpensive for audio snobs to take seriously,
2. it's never occurred to many audiophiles that a 4" driver could be their ideal solution.

 In Japan where audiophiles talk less and build more the FE103E and FE107E have what at times appears to be a cult following (Google "FE103E jp" and "FE107E" and see for yourself). This had not really sunk in when I hooked up my first pair of FE107Es. The numbers looked good and they were not busting the oneZ project parts budget. It was expected they would sound good. The actual sound this unassuming little driver delivers far exceeds the expectation of 'good'. The first attribute is a transparent directness which reveals both a wealth of musical detail and texture as well as the rhythmic pace and structure of the music. Then along comes some well recorded high frequencies and one is presented with the most delicate, almost ethereal, reproduction of treble. What does this thing think it is a 4 inch tweeter? Bass just jumps along and boogies in lockstep with the music and while hardly sub sonic in depth or room pressurizing in amplitude bass is so tuneful with the FE103/7E that part of the music is well covered. Imaging is outstanding with directional cues effortlessly portrayed in a Cinemascope wide arc extending well beyond the speaker pair outer boundaries.

Attempting to describe sound in words we almost invariably break it down into "the bass is this, and the mids are like that, and the highs are.....etc". Such analytic dissections largely miss the point of what happens when an FE107E is combined with an advanced enclosure and energized with the right amp. The result is all about a wholeness, a completeness throughout the range, and speaking with a single unified voice. Time and again one is struck by how direct and transparent yet utterly natural the music sounds.

materials

Have you ever seen a violin made out of MDF?

Conceptually and literally what an object is made out of in large measure determines its basic characteristics. When engineers are tasked with advancing the state of the art in their designs they often turn to more advanced materials. Titanium replaces steel and carbon fiber replaces aluminum the more advanced materials extending the device's performance envelope. When artists and craftsmen wish to elevate the objects they create the first order of business is selecting the materials most apropos to the work. Likewise in the artful craft of engineering hi-fi loudspeakers the choice of materials will have effects propagating throughout the design. The oneZ project aesthetics and engineering both aspired to an achievement beyond the typical. This calls for the use of atypical materials. The improbable pairing for this role are birch plywood and sand.

Birch-ply is a special high grade plywood made with thin layers of wood veneer and without the internal voids typical of construction grade plywood. The retention of wood's natural fibrous structure within the layers of veneer forming birch-ply make it very strong. With the material's strength coming from these fibers a large percentage of heavy glues and fillers is unnecessary allowing birch-ply to be light yet strong. Thus it matches well with the stiff & light criteria used in the oneZ enclosure design. On the aesthetic side of the design equation birch-ply has a smooth real wood grained surface and unique thin layered end which finds it often selected by modern furniture designers and art craft object artisans.

Sand is another atypical material when considering the majority of hi-fi speaker designs. Commercially it is just out of the question to ship devices loaded with heavy sand. And it is a marketing disaster with all the extra complexity and material cost required to use sand hidden inside the enclosure. That is a shame because as anyone who has ever tried to run across a soft beach can testify sand is unparalleled in its ability to absorb and damp out energy. For years I had read of early hi-fi pioneers who built speaker enclosures with double walled sand filled construction. This was filed away with other audio gizmo trivia. Then in a previous professional life working in the oil exploration  industry the fact that sound waves used for seismic exploration would not propagate through areas of sand peaked interest in this plentiful  material. If a dynamite charge or 60,000 pound vibrator cannot force seismic sound waves through sand what chance does a little speaker driver have?

Why is sand such an ideal material when the task is sound or vibration attenuation? Remember the First Law of Thermodynamics which states energy cannot be destroyed only propagated or converted into another form. Sound travels through air and solids as a wave form propagating from molecule to molecule. In a gas the molecules are light and undamped allowing the energy to jump from molecule to molecule with little loss. In solids the molecules are certainly heavier compared to a gas yet they are so tightly packed it again makes for efficient energy transfer through the material. Sand is of course a solid but when one backs out from the molecular level to the micro level we find it is in its characteristic form of grains. When vibrations attempt to propagate through sand thousands of individual grains are set into microscopic motion. Grains rub against each other and the result is friction leading to micro heating of the grains. Thus the sound/vibrational energy is converted to heat and the sound waves quickly attenuated. The key is the grains ability to be set into motion due to being loose yet packed together. This heating results in a vibration energy which is a noise in the speaker system becoming a heat energy which has no effect on the speakers sound. Some find this counterintuitive, for example thinking if sand is good cement must be better. WRONG, as anyone who has ever suffered through a night in a cement hotel where you can here every sound in the next room can testify, once the sand grains are cemented together the micro heating effect is 99% lost and all one has is another solid efficiently transmitting sound waves.

Recognizing sand's outstanding vibration attenuation characteristic is one thing, packaging it in a speaker based on a 'stiff & light' design technique is quite another. The sledgehammer approach of every wall being a double panel filled with sand is a budget buster and completely counter to the oneZ's aesthetic of simplicity. Where could the sand be used to greatest effect? Between the source of the unwanted vibrations and the structures which would propagate the noise into the air and thus to the listener. More redesigns resulted in oneZ rev. 7.x becoming rev. 8.2. Version 8 features a three layer front baffle an inch and a half thick. The center layer has internal cavities surrounding the driver mount filled with sand. Reaction forces propagating into the enclosure from the driver are damped by the sand in contact with the front baffle quieting it down. Waves traveling from the driver frame into the rest of the enclosure must first pass through the sand filled energy trap greatly diminishing their effects. Mechanical noise energy making it through the sand trap is then dealt with by the stiff & light enclosure architecture assuring very low cabinet noise levels yielding high resolution reproduction of desired signals.

style

    
The quarter-cubic-foot vented wood box is a classic form in modern hi-fi, it beckoned as the natural enclosure for oneZ. Style is one thing, function another. Only when the likely candidates for the system's driver proved ideal for this size and configuration did the stylist get his way. The classic rectilinear form ruled the oneZ style for both practical and aesthetic reasons. Practical considerations such as ease of setting up on stands or shelf, manufacturability, cost, and ease of assembly. Aesthetic reasons include the simple geometric shapes from which the classic box speaker is constructed and the need to blend into our living spaces already filled with rectilinear objects. Having settled on a classic form for oneZ the challenge became combining the classic with the new.

Bringing something new to a classic form is a common design challenge. A good example is a motorcycle. Long ago functional requirements evolved the form to always include two wheels on a mono track, engine in between, seat and gas tank on top. Yet within this classic form the spark of human creativity brings forth an infinite variety of designs. Some variety comes from emphasis on functional capability while other is purely style. The most successful designs seamlessly combine form and function using an emphasis on sculptural design and a delight in detail. The first step in implementing this is the sketchpad.

This early design concept sketch shows the design already on the path of using interesting unusual details and honesty in materials and response to function by the form. Sketched before driver size or enclosure volume were defined this drawing is grossly out of proportion yet it shows the desire to go beyond the ordinary.  At this stage the possibility of using interlocking finger joints between the panels was being explored.

This rendering shows the version of the oneZ rev 1 design ready to discuss with cabinet makers. Alas this led to it being abandoned as actually building such a design is a task for a master wood worker. It had been hoped that by laser cutting the panels it could be automated. The downside of that idea is that laser cutting wood leaves the edge charred resulting in deal killer appearance and odor issues.

                         

The design continued to evolve with ideas flowing and captured. Some to be discarded, others made their way into the final design.

Sketches and computer renderings can only go so far. Hand built prototypes moved the design forward both functionally and refining the styling.

With the oneZ design up to revision 7.2 styling details were 90% nailed down and the first machine cut prototypes were built. The sculptural design elements and details including curved rear edge of the side panels and squared vent ports are evident.

In a way this design was too successful as the oneZ rev 7.2 prototype's sound so exceeded expectations it was decided to take the aesthetic and functional elements out one step further in revision eight.

            

With oneZ rev 8.2 functionality and styling are both kicked up a notch with the major addition of a tri-layer front baffle. This implemented a rabbeted groove around the sides, top, and bottom above which the front baffle floats. Material and technique are celebrated as one inch of machined birch ply layers are revealed. Functionally the center layer of the tri-layer front baffle houses the sand making up the energy trap yielding a stable quiet reference surface for the drive unit.

The typical boring vent tube is replaced with a quad of square holes. Styling is enhanced as their shape and placement contrast and balance that of the driver.

As a final flourish the rear edges of the side panels sweep out in a graceful arc. Six holes penetrate the surface in a pattern reminiscent of the lightening holes used in aircraft structural members.

For those who want something unique the oneZ's front baffle can be custom ordered in solid hardwood. The special sonic and visual beauty of hardwoods add the final flourish to the oneZ while enhancing even the most sophisticated decor.








Taken as a whole the details used in oneZ emerge upon close examination to delight the eye yet effortlessly receded back into the whole  never dominating the object's classic style. Function dictates form, form yields up detail, detail is executed with style which completes the cycle returning to function.

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