EgglestonWorks: Design Philosophy

The design of each loudspeaker model in the EgglestonWorks line begins with the midrange. Since the midrange is called upon to produce the widest range of sound audible to our ears, its standalone performance characteristics coupled with its behavior once integrated within the loudspeaker cabinet are critical.

Sourced from Israel and manufactured under precise laboratory conditions, the midrange driver used in all EgglestonWorks products is a 6" polypropylene, double-magnet driver with a full 3" voice coil diameter. Unlike the midrange used in most competing high-end products, which typically possess a smaller 1" diameter voice coil, this midrange driver is capable of distortion-free sound reproduction under very demanding conditions.

Because it uses a 6" cone and a 3" voice coil, all the motive force comes from a point equidistant between the center and outer circumference of the cone. This balance results in a more piston like action with greater rigidity. This design is also far less susceptible to flexing at the cone edges - which can result in sound coloration.

The larger voice coil also uses a very large winding out of heavier-gauge wire than is used on a smaller coil. This makes for a much stronger motor and, assuming the proper current level, much greater control – greater ability to stop the cone from moving in the opposite direction. The stronger the motor, the more control you have over the extremes of excursion.

And because the coil is so large, it can handle extremely high current output. Without it, we would never be able to connect 6" drivers directly to the output of the amplifier - not even two of them. Our use of two 6" drivers in the midrange was integral to achieving the midrange characteristics we demanded. We have found that most speakers can clip on a raucous solo piano if they use a single 6" driver. We wanted no limit on the dynamic capabilities of the midrange, so we knew we needed to use two drivers.

Once we’d chosen that driver, we spent nine months just developing the crossover and the midrange loading. After extensive trial and error we arrived at the simplest crossover of all, no crossover. The two morel 166 drivers are connected directly to the amplifier. This is possible due to the Morel drivers smooth 6dB per octave roll off above and below its frequency range and ability to handle large power input without bottoming out or distorting. We didn’t even look at woofers or tweeters until we had assured ourselves that we were getting everything out of the midrange that was possible.

The simplest, purest, most uncolored approach is to design a system which allows the speaker drivers to operate in "free air," duplicating the motion of sound waves emanating from both sides of a musical instrument in live performance. This, however, is extremely difficult to achieve as any dynamic speaker with a cabinet has to manipulate the back-wave of the driver.

In a sealed-box design, you’re tuning against a certain air pressure to obtain a certain response characteristic. In a vented box, you employ resonances to achieve a lower cutoff frequency. The only box where you have the same air pressure behind the driver as in front is the transmission line. In a transmission line design, the line is equal to a quarter wavelength of the resonant frequency of the driver. Usually you wrap the line so the output comes out the front, in-phase with the output of the driver, which reinforces the bass output of the driver. We weren’t interested in this characteristic - all we wanted was a free-air characteristic. And we didn’t have room for two 5’ transmission lines inside the small cabinet we intended to build.

So we re-evaluated the whole approach to transmission lines. We worked with experts in the field of stuffing material and decided on a specialized acoustic stuffing material known as acousta stuff. "Acousta stuff" is a polyester strand which is crimped every millimeter. This makes each strand a complex shape, capable of providing greater diffraction to the sound waves traveling through it.

And because the strands interlock, they never settle. The result is a material which slows lower frequencies while attenuating the higher frequencies. After an extensive amount of trial-and-error experimentation, we determined the exact ratio of cabinet length to stuffing weight we needed for a quasi-transmission-line loading. What we ended up with performs extraordinarily well - I’m not aware of any other speaker on the market which shares this loading system.

Creating a bass section that possesses the same free-air characteristics of the midrange proved challenging. To solve the problem, we mounted two 12" drivers in a pressure driven configuration. Inside the speaker cabinet there are two parallel chambers, with one 12" driver mounted in front of the other.

The inner driver, which is in a ported box, acts as a servo behind the outer driver. This allows the drivers to efficiently produce a lower frequency response because the drivers see an effective cabinet volume that is twice the actual cabinet volume.

The tweeter section was the last section we focused our design efforts upon. And here again, we were striving to produce a system which exemplified the same design philosophy that went into the other driver sections -free-air. We choose the Esotar tweeter because it has its own aperiodic damping chamber and has the largest vent on its pole piece we’d ever seen on a tweeter. With this vent and large chamber, the tweeter doesn’t see any back air-pressure to speak of, allowing it to operate in free-air. A final advantage of this tweeter is that its crossover is as simple as can be, consisting of one Hovland Musi-cap and two Vishay resistors as an L-pad.

To purify sound reproduction and eliminate resonances in the chamber walls. We developed a cabinet constructed of 5/8" thick MDF wood panels twice laminated with a rare viseolastic damping material imported from Sweden.

As a final measure, fine Italian granite is adhered to the outside walls of the chamber (3cm for Andra, Ivy and Andra Center; 2 cm for Rosa; 1 cm for Isabel and Fontaine). The inert mass of the granite functions to reduce cabinet resonances in the crucial midrange section of the loudspeaker to a vanishingly low level.