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Into the mind of Albert Von Schweikert, Part II of III

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Midrange

At the beginning of my audiophile adventure, I used Quad and Acoustat electrostatic drivers for the midrange frequency band in my hybrid speakers using my own design of subwoofers and ribbon super tweeters. Later, I used ribbon midrange panels in my quest for transparency. Although these planar drivers sound quite good in many respects, I measured (and heard) distortion caused by resonances due to the clamped edges of the diaphragms, lack of adequate excursion potential, and narrow dispersion caused by the wide panels themselves. Due to the lack of efficiency, dynamic range was also greatly compromised – to the extent that I quickly realized that the development of a better cone-type midrange was necessary.

Although there are planar fanatics that will call my words “heresy,” it is easy to show the distortion in these so-called “reference” planar midrange units. If you have seen John Atkinson’s excellent measurements of planar speakers in Stereophile magazine, you will notice that their “waterfall” plots (known as Cumulative Spectral Decays) have incredibly high levels of ringing due to the clamped edges. In other words, the energy is not damped by an absorbent edge (made of rubber in a cone driver), but is reflected back into the diaphragm by the clamped edge of the wood and/or metal frame. This is similar to the resonances heard in a drum, i.e., the creation of a single note rather than the neutral replication of a signal.

The VR-4 designs since 1978 have used cone drivers with “exotic” cones made from lightweight materials, driven by very strong motors. The first model, the Vortex Screen, used a rubberized Kevlar diaphragm, while later models used a woven carbon fiber fabric diaphragm. The newer models from 2001 use a patented cone material called “Aerogel,” which is a mixture of paper fibers, Kevlar threads, carbon fiber powder, and several types of binding chemicals. The Audax (of France) versions have a top coating of a damping liquid that is black, dark green, or powdery gray in color, depending on the driver model, while my proprietary designs built in my Asian factory use the black polymer liquid coating exclusively. All of these coatings are used to reduce cone flex and flatten the peaks caused by cone excitation, eliminating the so-called “cone cry” existing in plain paper, ceramic, or metal cone midrange drivers.

In addition, all of my custom-designed Audax models use a single-layer ribbon voice coil driven by an enormous magnetic system, enabling transient response speed as fast as any planar driver, but with an extremely important upgrade: the suspension is designed to be extremely absorptive of unwanted energy traveling through the cone material.

The combination of these different aspects of the midrange driver’s engineering “target” result in extremely transparent sound quality exceeding any planar speaker we have ever tested. Our “live versus speaker” testing has proven time and time again that a well designed cone midrange can greatly exceed the transient response, impact, dynamic range, power handling, and sheer realism of any planar driver made. In a direct side-by-side A/B comparison test using a live voice feed, using world-class mics (Neumann M150 tube condenser mic, Rhode NTK tube omni condenser mic, AKG S1000 solid state measurement mic) along with our custom-built mic preamp, the midrange frequency band of the VR-4 speaker system has been found to be more accurate than any other speaker we have heard or tested. In fact, in the past several months, we have taken in trade two pairs of Quad 989 electrostatics and one pair of Genesis 300 planar speaker systems on the VR-4 SR Mk2. (Customer references are available on request to qualified reporters and/or researchers). All three of these customers brought their speakers here to experience the A/B/X test for themselves, and they ended up taking home VR-4’s! Note that the Genesis 300 ribbon system retails for $30,000 while the VR-4 retails for $12,000.

Treble

As Robert Harley noted in his review of a very expensive and well known speaker system a few years ago in The Absolute Sound, most dome tweeters exhibit distorted and shrill high frequencies, compelling him to call them “nasty little resonators.” I quite agree!

Although I have used some metal and ceramic tweeters in the past, I had them specially damped with a thin, clear butyl rubber layer. Since this was a very tedious process and greatly reduced the efficiency of these hard-dome designs, I wrote a new design target in 2001 to employ only silk dome tweeters. Why generate metallic resonances when you don’t have to, I asked myself?

The Vifa (Scanspeak designed) Dual Ring Radiator we use in the VR-4 SR Mk2 system is a silk dome tweeter formed into its characteristic shape by the voice coil attachment to the midpoint of the dome itself. This patented design results in several amazing benefits never before achieved in a dome tweeter:

a. Flat response up to 40kHz in the Vifa version used in the VR-4 SR Mk2. Many customers ask why we use a tweeter that exceeds the frequency response of the digital Compact Disc, which reaches only 21kHz at best. The answer is: review your basic mathematics. If you study the Hilbert equations carefully, you will find that phase shift begins at CUTOFF FREQUENCY/2, in other words, the phase is only flat to 10kHz in a device that extends to 20kHz, then phase rotation begins it’s eventual shift to 89.99 degrees. Yes, that’s correct: the tweeter’s phase and amplitude are not in sync with each other at the top end of its operating bandwidth! By designing a tweeter that is flat to 40kHz, the phase shift does not start until 20kHz, enabling flat phase and frequency response to the cutoff point of Compact Disc. This phase/frequency coherence can be heard as heightened 3-d image focus, where the instruments are floating in space all over the front of your room. In addition, the sense of “air” and detail is extremely realistic, but natural and lush; never harsh or bright.

b. Extremely low distortion due to smaller diaphragm surface area that is not directly driven by the voice coil and the use of the rubber coated fabric diaphragm that does not “ring;”

c. Wide dispersion achieved by the smaller ¾” inner dome;

d. Extended midrange response and power handling enable by the outer 1.5” outer ring;

e. Controlled dispersion achieved by the use of a phase plug in the center of the twin rings;

f. Higher power handling before burnout due to the use of Ferrofluid cooling liquid in the magnetic gap.

DS: Some speaker manufacturers prefer the use of silver wiring internally for certain drivers versus copper. What materials do you prefer in the construction of your speakers? Do you have a preference in whether copper or silver speaker cables are used with them?

AVS: I’ve built many speakers on a custom basis using silver internal wiring, but voiced the speaker to sound “neutral” rather than “ruthlessly revealing” that some people believe is the sonic signature of silver cables. It is true that solid silver in a very pure form has more “detail” than copper wire, especially in the high frequencies. However, silver plated copper wire is schizophrenic in my opinion, and it’s useful for only bass frequencies. If you’re going to use silver, then use the highest quality of solid silver you can afford.

I must say that copper and silver wires are NOT inter-changeable unless the system is “voiced” to accept the type of cable. Since most of my customers seem to like copper wire’s mellower sound quality and the lower price, we wire the speakers with copper in their “stock” form. However, for a customer that has silver wires throughout his/her system and wishes to have that same brand of silver wire inside the speaker, we can accommodate the request but will charge an additional price based on the difference in cost. Our stock copper internal wiring is made for us by Analysis Plus and is used on models VR-4SR upwards to VR-11SE.

When we debuted the VR-10 Armageddon speakers at CES in 1993, we won Stereophile’s Best Sound Of The Show, awarded by Guy Lemcoe, using $50,000 worth of Van den Hul silver cabling from Holland. Van den Hul also supplied the internal wiring of that particular pair of VR-10’s that were later purchased by Jim Wald, Bill Gate’s Chief Accountant at Microsoft.

If affordability is your goal, along with high value, go with pure copper. If you can afford the high tariff, go with silver but do it right: don’t mix copper and silver wiring together in the same system!

DS: Should there be any concern over an over-zealous audiophile jamming his hand into the bass module’s cavity while stuffing it with polyfil? Can any of the components be damaged, such as drivers?

AVS: As you’ve now read the VR-4 SR Mk2’s Owners Manual, available on-line at our website, you have discovered that the customer can “tune” the bass response to his room, taste, or equipment. My woofer loading design is a hybrid (quasi) transmission line, which is a fancy way of stating that it is an overdamped ported box using an “aperiodic” alignment based on filter network theory, empirical experiments, and the testing of every type of bass loading design we could find in textbooks at Cal Tech.

The bass tuning is altered by physically changing the stuffing density of the internal damping material, which is Dacron polyfil. It is nearly impossible for someone to damage the drivers when adding or subtracting Dacron from the port. In addition, the change is made in only a few minutes and is reversible, so no damage can be done to the sound quality.

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