VR-4 White Paper

Not just another speaker!

Albert Von Schweikert’s design goal for the last 20 years has been to recreate a simulation of a live musical event. Not satisfied with conventional technology which he felt had been exhausted, AVS’s recent research indicated that more realistic sound quality could be obtained by replicating an acoustic inversion of the microphone. After all, it is the microphone’s signal which is recorded, not the actual music itself.... In addition, Albert’s design team determined that 4 dimensional “planes” had to be optimized, hence the designation virtual reality in 4 planes, or "VR-4".

These four planes are defined as Amplitude, Phase, Time and Space.

1] AMPLITUDE

The total sound output, including both fundamentals and harmonics, must be reproduced equally throughout the entire ten octave bandwidth of the speaker system. This must be accomplished not only on-axis in front of the speaker, but also to the sides. Conventional systems often ignore the sound radiated off-axis, resulting in poor response reflected back to the listener from the walls, floor, and ceiling.

This poor off-axis response is heard as coloration and lets the listener know he or she is listening to speakers instead of a live event.

Harmonic Balance
Next, the harmonic structure of individual instruments is determined by relative volume levels between the fundamental and overtone. This timbre which is composed of harmonic structure is critical for you, the listener, to easily hear the difference between a Steinway or a Bosendorfer grand piano. Many conventional systems do not sound like they have flat response due to harmonic imbalance, even though they measure reasonably flat. The VR-4 has been optimized to present these important harmonics in proper perspective and was accomplished by exotic cone materials combined with a new type of filter circuitry.

Conventional crossover circuits used by other manufacturers chop the signal into pieces and feeds these pieces into drivers which have very dissimilar sonic signatures. The resulting colorations combine and result in a great loss of coherence. Sound familiar?

New Circuit Design
The new VR-4's Global Axis Integration Network TM harmonically blends the signals at frequency dividing points outside of the ear's most sensitive regions. This technology does not allow the drivers to be identified as the source of the signal. In addition, all five drivers have been modified and/or designed to have similar tonal characteristics at their overlap points. These techniques allow the VR-4 to sound like a single element speaker with the attendant increases in coherency and wide, even dispersion. As a matter of fact, the VR-4 design is essentially a one-way system with augmentation in the sub-bass and overtone-treble ranges. In this manner, the coherency and resolution approaching the recording microphone is achieved. This may sound deceptively simple but proved to be a significant engineering challenge that took many years of transducer and circuit design to achieve!

Low Level Tonal Balance
The ideal system must maintain equal tonal balance between bass and treble registers at every volume level. Unlike many systems, the VR-4 can reproduce deep bass even when listening quietly, allowing greater shades of dynamic contrast.

In addition, although it is often thought that phase response alone determines good sound staging, precise imaging and depth retrieval each depend on accurate volume level differences, relating to the distances between individual instruments and the microphone.

The VR-4 has been engineered to reproduce amplitude in all forms with extreme precision, resulting in the highest level of accuracy.

2] PHASE

The phase response of the VR-4 was engineered to create the illusion of a single element speaker. This has been achieved by means of a new circuit which blends the drivers harmonically with respect to the time coherent driver voice coil offset.

Our revolutionary circuit, The Global Axis Integration Network TM is of particular benefit to all listeners because the huge soundstage is spatially realistic and all-encompassing. Depth of field is awesome, making the presentation virtually three dimensional. This depth and image enhancement has been accomplished by special phase compensating circuits to achieve the harmonic driver blending which relies on inter-driver phase behavior.

When listening to performances on the VR-4's the old days of having to sit in the "sweet spot" are over!! The entire room becomes the sweet spot unlike many systems with narrow or beamy response.

3] TIME

Voice Coil Alignment
temporal alignment of the transient response of all five drivers in the VR-4 is a critical aspect of the design. True dimensional focus is provided by time and phase alignment of all drivers in the system and is again governed by the absolute voice coil relationships and their physical mounting offset. The acoustic focal points were determined by FFT (Fast Fourier Transform) impulse response tests.

Transient Response
Proprietary driver design and/or modifications result in matched transient response for all five drivers. Many conventional systems suffer from the use of drivers which do not respond in the same manner to tone bursts, resulting in blurry sound. Since transient response is also disturbed by reflections from the surface of the enclosure, we have eliminated these reflections by the use of absorptive materials on the surface of the midrange/tweeter enclosures. This is the main reason for our use of the sock covering the assembly, as the cosmetics would not be acceptable if the absorptive materials were placed on exposed cabinet surfaces.

Woofer "Speed"
It is well known that perceived woofer "speed" sets the music's timing and pace, so special attention was given to the woofer/cabinet loading to prevent "hangover". Bass response down to 20Hz is achieved with authority, clarity and articulation. The VR-4 woofer system is optimized beyond any other full range speaker available, even very expensive subwoofers.

4] SPACE

The illusion of Virtual Reality depends on spatial images created by an invisible source. Thus, Acoustic Inverse Replication TM of the microphone's pickup field enables the VR-4 to recreate the natural acoustic space encoded in any recording medium. The air and space around each instrument is highlighted as well as the acoustic space at the recording site.

Conventional technology has been likened to hearing music through an open window. Von Schweikert Research asks.......... why stand outside?

Engineering Details

CIRCUIT DESIGN

The global axis integration network TM is the most important aspect of the Acoustic Inverse Replication TM concept. This circuit achieves the sound of a single element speaker to duplicate the average microphone's pickup pattern. As the GAIN design enables all five drivers to radiate sound equally in a 180-degree global axis, the VR-4 recreates the virtual reality of live music as picked up by the microphone.

Providing flat off-axis response in both frequency and phase, our circuit offers the benefits of 24db acoustic slope performance without the drawbacks. Our custom engineered harmonic filters deliver extreme clarity by reducing driver interference associated with excessive overlapping acoustic output.

Typically, complex series circuitry reduces dynamic range due to parasitic absorption by the filter components themselves. However, we have achieved high transparency by using novel filter designs, whereby impedance, phase, and amplitude compensation have been designed in parallel circuits. This of course permits a more direct signal transfer.... why listen from outside the window?

ENCLOSURE DESIGN

Two piece construction: To greatly enhance clarity, the VR-4 design is a two-piece stacking system with the top unit containing the midrange and tweeter, and the bottom unit containing the woofer/sub-woofer. This dual-box design reduces panel resonance and vibration and results in superior sonic transparency over single-box designs.

Minimum Baffles: To enhance wide dispersion and replicate the microphone pickup, we use minimum baffles on both the midrange and tweeter. Thick absorptive acoustic felt covers all exposed surfaces adjacent to the drivers. This prevents diffraction which causes a "ghost image".

Spatial Alignment: To preserve the time and phase coherency of the individual driver outputs simulating a "one way system" such as the microphone, the driver acoustic centers have been aligned using impulse response technology.

Constrained layer damping: To minimize enclosure panel vibrations to the inaudible levels necessary for virtual reality, a three layer wall is used. The thick internal layer consists of a vibration damping material similar to "silly putty" selected for it's ability to absorb resonance. Common bracing techniques merely spread the resonance through the cabinet walls and allows ringing. It is well known that MDF is non-lossy and "rings"; this can be demonstrated by putting your ear against even the best braced cabinet and listening to music. Bracing in itself does not eliminate the ringing, so this distortion must be filtered out using our exclusive damping techniques. As we say, the only "good" resonance is a dead resonance !!!!

BASS SYSTEM

Epoxy cones: To achieve 20hz bass response with power and articulation, 8 inch hybrid woofers were designed with epoxy cones for extreme stiffness. Cone flex in conventional woofer cones contributing to muddy and slow bass response has been eliminated. In addition, we found that twin woofers with smaller diaphragms have far greater transient response speed and articulation over one larger driver.

Distributed resonance induction circuit: Operating in conjunction with the crossover, this circuit eliminates a common impedance peak found in ported systems and also greatly increases amplifier efficiency in the critical bottom octave, allowing 20Hz capability. This VR-4 exclusive enables infra-bass response necessary for true realism in a modestly sized enclosure, since ultra low frequency reverberation adds greatly to perceived "hall" size.

Dual tuned chambers : To reduce excess overlap between twin woofers, separate enclosures and tuning frequencies were engineered to eliminate mid-bass heaviness. Speed and articulation are greatly enhanced, allowing individual drum strokes to be perceived. Common woofer tuning methods result in bass "roar" on these same notes!

Dual crossover frequencies: Both woofers operate down to 20Hz for sub-bass impact. However, to maximize the linearity of the response, separate crossover points are used at 60Hz and 125Hz, eliminating the mid-bass thickness which plagues other designs.

MAINDRIVER (MIDRANGE) SYSTEM

Labyrinth enclosure: To reduce backwave reflections, a labyrinth with non-parallel walls channels the energy away from the driver, preventing the most common cause of coloration. Gradient Density TM stuffing technique was developed to gradually absorb the rear wave, preventing reflection of the unwanted energy back into the cone.

Advanced midrange driver: To achieve utter transparency to virtual reality levels, a very highly developed driver is used. First, the natural frequency response of 57Hz to 12,000Hz permits almost full range application without crossovers in the ear's most critical band. At the VR-4's crossover points of 125Hz and 3.5kHz, the driver is "coasting" effortlessly. Second, the carbon fiber cone has a very high Young's Modulus, or stiffness to weight ratio. Naturally, a stiff and light cone will have less distortion caused by either excessive weight or cone flex. In addition, traps formed by the weave absorbs energy traveling on the surface of the cone. Third, the cone's edge is bonded to a special energy-absorbing rubber compound called "Norsorex" which offers several times more damping than butyl or foam rubber.

To eliminate distortion and increase dynamic range for startling "jump factor", the voice coil is an aluminum ribbon wound on edge to maximize energy transfer. Last, the thick cast aluminum frame eliminates the ringing generated by commonly used inexpensive steel frames.

This is the best midrange driver we know how to build, cost-no-object.

TREBLE SYSTEM

MODIFIED TWEETER DIAPHRAGM
Harsh treble, seemingly disjointed from the midrange frequencies, is a common byproduct of ordinary dome tweeter design. Consequently we engineered a diaphragm which has no break-up or ringing. This was achieved by damping an aluminum diaphragm with a rubber coating, allowing both clarity and sweetness in the same driver. In addition, a heavy Ferrofluid damps the voice coil vibration and also cools it during periods of high power input. Although our tweeter is flat to 25kHz with attendant "air" and space, it's harmonic overtones are completely blended with the midrange fundamentals, eliminating both coloration and listening fatigue.

HARMONICALLY CORRECT TWEETER FILTER
Ordinary treble crossover circuits do not damp excessive out-of-band diaphragm motion sufficiently, allowing ringing and/or distortion. Our GAIN circuit compensates for both the tweeter's impedance and phase anomalies, enabling smooth integration to the midrange driver. In addition, the circuit employs expensive polypropylene capacitors and air core inductors which have neutral sound quality. Many hours of listening tests have been conducted to determine the brands and types of filter parts used in the VR-4.

Finally, experience the thrilling realism of rosin on a violin bow without being reminded of the sound of fingernails screeching on a blackboard !!!!!

REAR AMBIANCE DRIVER

To simulate the reverberant characteristics picked up by the microphone at the recording site, we have integrated a 2" rear firing mid/tweeter driven by a specialized signal. Since time delay and phase information is contained in the signal present at the microphone from the rear and sides of the recording axis, this signal must be reproduced by the speaker in order to recreate the original depth and ambiance of the recording site.

ATTENUATOR

We have provided an attenuator control for the rear driver to reduce the high frequency energy to compensate for program or room imbalances. These controls do not reduce the transparency of the drivers, since they are normally out of the circuit. Fixed resistors are used to set the volume to flat response so that the attenuator can only be used for level reduction.

BIWIRING CAPABILITY

Both the woofer and midrange/tweeter modules have separate inputs to permit biwiring or bi-amping. We recommend biwiring to realize the maximum level of transparency.

BINDING POSTS

We use CARDAS TM binding posts exclusively, having found no superior wire terminator. These premium gold and rhodium posts allow very high torque to be applied without stripping the threads or rotating the posts in their seats. (Electron microscope photographs show less than a 30% contact area with ordinary connectors. The resulting arcing leads to glare in the treble.) By tightening the connection with sufficient force, a gas-tight seal with double the theoretical contact area is provided, allowing much smoother highs and a superior focus.

SPIKES

Four heavy duty spikes 3/8" in diameter with locking nuts are provided with each speaker. These are mounted to the base of the speaker with threaded female metal inserts and are adjustable for both height and rake angle for individual situations.

COSMETIC FEATURES

For universal cosmetic appeal, the cabinets are wrapped with an acoustically transparent black cloth. Fine furniture-grade hardwood end caps made of solid and veneered hardwoods are finished by hand using premium stains. For maximum aesthetic appeal, all corners and edges are radiused. A clearcoat finish for both durability and cosmetic appeal is applied. COLOR CHOICES
Three distinctive finishes are available for the hardwood end-caps:

Cherry. This is a brighter red finish often seen on furniture. (Optional, extra cost).

Clear Oak. This is a light shade similar to unfinished pine or birch. Deep woodgrain adds texture. (Standard finish)

Black Oak. Oak, medium grain, with satin gloss black finish. (Optional, extra cost).

TEST PROCEDURES

Each and every component of the VR-4 system is tested prior to assembly, from the five drivers to the crossover parts. In addition, after the subassemblies are completed, the finished crossover boards are tested using a computerized program. Finally, after 48 hours of break-in, the finished system is tested for distortion, frequency, and phase response. Listening is done to each and every pair to assure that your pair is identical to the original prototypes.