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Why is time/phase coherence important in loudspeaker design and when did you discover this?
Time and phase coherence are necessary to preserve the shape of the complicated ever-changing waveform we call music. When we hear that waveform in its entirety, we get the music's message, its meaning and easily discover how the music is flowing through us not stopped by something heard as artificial, something we are too willing to blame on studio antics or on some other component in our systems or on room acoustics or poor setup.

Most loudspeakers severely scramble the time arrivals of the different tones of music. How much and where in the tone range the time delays occur depends on that speaker's design. In my experience, a speaker's lack of time coherence is one of the main reasons that speakers sound different and why conventional measurements (which do not consider time arrivals) fail to predict how a speaker will sound.

The first time-coherent speakers I heard were the KLH and the Quad electrostats in 1973 when I was investigating which high-end stereo I should buy. It was easy to hear how they presented the music with far more grace and clarity. However, I did not enjoy their limitations so I kept looking.

In the fall of '73, a local high-end audio store started assembling and selling a large bookshelf design that used dynamic drivers. Side by side, it blew away all of the highly-regarded dynamic speakers of the time from Klipsch, JBL, Dahlquist, IMF, Celestion, KEF, Infinity, Advent, Rogers, RTR, Cerwin Vega, Jordan, AR, Bozak and many more. There was no comparison. To my surprise, I learned how two talented electrical engineers at HP had designed these speakers. I too worked at HP at the time building the highest speed oscilloscopes on the planet. I asked them what made their speakers sound so good. They responded, "These use simple first-order crossovers, which is the only circuit that keeps the (three) drivers synchronized, drivers that are also naturally very smooth in their frequency response. We also make our own live recordings of classical music." I bought the speakers with more than two months' pay.

Of course, I kept asking them questions about speaker design and they did me the largest favor for what was to become my career. They gave me a set of reprints on loudspeaker design from the Audio Engineering Society, all of the marvelous, fundamental research that had been done since the 1930s. They said, "Read these and come to understand all aspects of this body of knowledge - mechanically, acoustically and mathematically. Then you'll have the foundation for advancing speaker design. If you do not, you will be reinventing the wheel. We only created our speakers on a whim, knowing that time-coherence was an important consideration for good sound. Study hard and you can do better."

I built my first pair of time-coherent speakers in 1974 by putting those HP speakers' drivers into physical time-alignment inside minimal cabinetry and adding the first Motorola piezoelectric super tweeter for a 10" 4-way design. These speakers had double-walled woofer cabinets, flat response from 30Hz to 30 kHz and reproduced square waves in the midband. Looking back on that time, I think few others had ever moved their speakers out away from the backwall and set them up by today's audiophile standards. I also purchased Koss' ESP-9 electrostatic headphones for a reference comparison (truly time-coherent headphones with tremendous dynamic range). They had flat response from below 10Hz to, I think, nearly 100kHz. I still have them.

During these formative years, I met Jeff Rowland at the same audio shop. I was still at HP and he was a technician at Ampex, experimenting with his own amplifier and preamp designs. We had many interesting times together. In 1978, he had gone into business and soon built me a monstrous Class-A amplifier.

That original 10" 4-way was to remain a research test bed for me throughout the remainder of the '70s. In it, I tested the latest drivers including the first Technics and JVC planar/ribbon super tweeters and refined my first-order crossover circuit. I left HP's employ in 1976 and went to work in the audio industry, moving between retail, consulting, pro sound and back to high-end retail management. I was able to audition and test most all of the highest-fidelity components with my speakers, which helped me enormously. I also sold just about every brand of high-end loudspeaker available and was able to analyze what they had done both right and wrong.

After 1981, I moved into pro sound and recording full time and continued my speaker development on the side, selling a few pairs here and there. I returned to the university in 1986 to obtain a Bachelor's and Master's in solid-state Physics. In 1988, I officially founded Green Mountain Audio, producing a few pairs of a conventional speaker with a first-order crossover, the M-3, a 10" three-way with a Dynaudio tweeter. During that period, I also designed and installed huge foreground-sound systems for a national chain of billiards parlors. They wanted the highest-quality sound from their CDs for rooms of up to 15,000 square feet. Usually, 30 sets of 15" three-way speakers with first-order crossovers were bi-amplified and driven by about 8,000 watts. I also was hired to consult on hydrodynamic-force measurements projects with the US Olympic Aquatic Research Center and taught undergraduate lab classes. But I still worked on my designs, thoroughly exploring transmission lines and their variants. In 1989, I began my work on our Imago model and in January 1991, took it to the CES in Las Vegas. The response was such that I never could take those last two classes in quantum mechanics to finish my Master's degree (I had not taken the thesis option).
What was the first loudspeaker you heard that really impressed you?
Actually, that would be the sound from the cone tweeter of a bookshelf Fisher loudspeaker. It was the summer of '69 and I had just gotten my driver's license. I drove down from Green Mountain Falls into the city to explore the only "high-fi" shop in the area. The local classical station was playing and I happened to walk right in front of that tweeter. From it, I clearly heard the concert-hall echo to a degree where I could tell how large the hall was and how the musicians were arranged. It had not occurred to me that spatial relationships could be heard to that level of realism, to that level of fidelity. I still remember exactly how that sounded. Of course, by today's standards, the sound would be unexceptional but I later discovered that these tweeters used a first-order, minimum phase shift crossover.
Why aren't there more time/phase coherent speakers on the market?
I think for several reasons:
  • They present unusual challenges to a designer's choice of drivers. Wide-bandwidth drivers are few and also expensive. A computer-aided higher-order crossover better protects an inexpensive tweeter and sounds higher-tech for marketing purposes but then you have extreme phase shift and many circuit parts to pass the signal through.

  • Most speaker designers, from what I see, are not versed in time-domain math. This is very difficult to learn. After the mid-70s, it was discarded from the electrical engineering curriculum and replaced by math for digital systems. It remained a subject only taught to Physics majors.

  • Beyond those technical difficulties, I think that many designers do not know what they need to hear. Most seem to have never spent large amounts of time on stage with first-rate musicians and singers. They need to know real timbre, rhythm, timing and dynamics by training their ears to hear time-coherent sound from good headphones such as from Grado or Stax. They need to regularly attend live, un-amplified music performances without regard for genre including events in small auditoriums, in someone's home, in a church or local Jazz club. They are being paid to know what is coming into their speakers so they can tell if it's coming out correctly.

  • Many do not test their designs with a truly wide range of music and recording styles. I see them declare a recording has problems yet when heard on expensive headphones (which are usually time-coherent), it clearly does not. It is the phase errors in their speakers that make those recordings sound unlistenable.

  • Most seem unfamiliar with how a microphone modifies an artist's sound. A microphone does not know left, right, up or down. Those multiple dimensions are compressed into the one dimension of "how far away". They need to visit studios to learn that what the microphone hears is different from what they would hear in front of the singer. Then they would learn some of what any studio has to do to that sound to make it seem natural.

  • Some do not understand exactly how a listening room modifies the sound we hear and in what tone ranges our ears integrate reflections with the direct sound or depend on time-arrival differences to differentiate between the playback room and the acoustics of the recording. I always see high phase-shift speakers judged "very particular" about room placement.

  • Many do not know how the sound waves change as they move away from the cabinet. The math behind radiation resistance drilled into any pro-sound speaker designer begins to tell you this.

What are other important requirements for a good loudspeaker?
  • The enclosure has to be designed for minimum surface reflections from the drivers over most tone ranges. A curved front baffle is not enough and the math shows this easily. The most annoying reflections are those heard as a splash in the low treble. So, many designs have staggered crossover-points between the mid and tweeter to introduce "what measures as a slight dip in the on-axis response." That splash is still there but at least the test microphone is happy and the favorite female singer does not spit anymore. Yet you get even more phase shift between those two drivers, which affects clarity, rise times, front-to-rear depth and sharpness of the image. You also have an unusual load for your amplifier, a varying load that causes tube amplifiers to change their tone balance and solid-state amplifiers to sound strained or sometimes "thin".

  • The enclosure has to be as rigid as possible and also mechanically well damped in all possible degrees of motion, including torsional vibration modes, shear modes and surface-wave modes. Yet, many designs use a cabinet, which is deliberately allowed to vibrate - many UK designs come to mind. In the simplest analysis, this vibration "leaks bass" and generates what sounds like out-of-phase scratchy "noise" in the midband. Just put on a stethoscope to hear that. However, their designers made those choices because a simple MDF cabinet is even worse at generating that mid-band noise (the UK cabinets are at least plywood). There are other technical reasons that thin-walled cabinets can seem to be good choices but they always lose to a rigid, inert cabinet. The difference is clarity on complex music and in the dynamic response and overall sharpness of image.

  • The inside of any enclosure must be as quiet as possible at all frequencies except the lowest bass where the internal air pressure must respond to the woofer motion without delay. Thus in the low bass, sound-absorbing materials must become transparent to sound. This is particularly difficult and misapplication of absorbent materials is widespread. Some designers conclude that an enclosure should have no acoustic damping materials at all. Yet a series of properly conceived experiments would have revealed the correct type and placement of the materials.

  • The drivers must be selected for maximum cone stiffness and for high internal damping of the cone material at the frequency where they do break up. This always happens but the break-up frequency must be far beyond the actual crossover point and well damped.

  • The drivers' suspensions need to be very supple to let the cone/dome move on both the smallest and largest of notes.

  • The lighter the cone, the more flexible its suspension must be if you are to have a driver with a naturally flat tone balance. Extremely flexible suspensions are rare as that "limpness" is very difficult to control in a production run of thousands of drivers.

  • Any driver's chassis must be well ventilated to reduce thermally induced power compression. This helps the sound remain dynamic when the music is loud and/or complex.

  • Driver chassis must be stiff in all degrees of freedom and well damped against ringing. One mode of vibration that often goes unnoticed is that the woofer magnet likes to vibrate up and down. Viewed from the side, it resembles someone on the end of a diving board. This flexing can be seen in the driver's raw impedance curve as a small wrinkle.

  • The magnetic field around the voice coil must be as constant/uniform as possible. This is a main requirement for the driving force to remain constant, no matter the position of the voice coil, and to reduce distortion.

  • The crossover circuit must be very simple while preserving time-coherence/phase. There are many capacitors that do not pass small signals! Others do not have a proper tone balance on music yet measure excellent on test tones. Many inductors ring at certain frequencies. Other inductors do not behave closely enough to ideal with regards to phase between voltage and current.

  • It is not enough for a speaker to be merely "a phase-coherent design". Phase coherence means that at their crossover point, two drivers produce sine waves that are in phase on the peaks and valleys. But if you look at the beginning of that sine wave signal, one driver starts before the other - exactly one full cycle earlier. At the end of that sine-wave tone burst, the other driver stops one full cycle later. Time coherence means that the beginnings and ends are in full synchronization.

  • I have found it unacceptable to use a complex crossover circuit to force a driver to have a first-order acoustical crossover rolloff. The signal must pass through many far-less-than-transparent parts and also down printed circuit-board traces. While the resultant load on the amplifier may appear benign, it is not as the sound of those speakers changes noticeably with each amplifier. Finally, such a designer is electrically correcting for problems, which are actually mechanical or acoustical in nature - such as cabinet reflections. The reflections still exist and the direct sound is heard to be somehow "not right".

  • A speaker crossover cannot consist of only a capacitor on the tweeter with no complimentary inductance on the midrange driver. Many audiophiles and some designers believe that using this near non-existent circuit is a good thing. It is with the right midrange driver when compared to the speaker with a typical complex crossover. However, the resultant response from the tweeter seldom has the phase and amplitude characteristics of a true first-order rolloff. Also, the designer is relying on the midrange driver's cone to go into break-up in order to roll off its amplitude (loudness) where it meets the tweeter. Furthermore, that mechanical rolloff nearly mimics the phase and amplitude characteristics of a second-order filter. Thus, the combined response of mid and tweeter is not even close to time coherent but the sound certainly can be more pleasing than designs with complex crossover circuits.

  • Single-cone speakers have cone breakups causing a rough treble response and are thus time-incoherent in their highs. Because of their intentionally limited stroke, the bass disappears when you push the volume to loud levels. Their cone breakup and/or their mechanical crossover to a whizzer cone (by definition) prohibit the treble output from being time coherent with the midband. You can see cone breakups and resonances as wrinkles in the impedance curves of the raw drivers and sometime in that of the finished system, even in a multi-way design.

  • Use only one driver per frequency band. If you double the woofers, they should only operate at frequencies with wavelengths far longer than both woofers' combined diameters. Line sources are line sources only across a narrow range of frequencies. The math clearly shows this. Having multiple sound sources for identical frequency coverage leads to image instability and imprecision with each movement of your head.

  • Don't use a driver that has a severe peak in its response. Many think that a notch filter in the crossover circuit or via a TACT-style digital compensation unit will suppress that ringing. It does on a sine wave test. But that mechanical resonance will still be triggered by sub-harmonics of that frequency at either 1/2, 1/3rd, 1/4th of that frequency.

  • Any testing must include the time domain performance of the speaker. Observe that magazine testing of time-domain performance does not extend much below 1kHz yet the majority of music occurs below 1kHz. You are thus given no idea of a speaker's time-domain behavior for its woofer vs. its midrange driver. Outdoors or anechoic-chamber testing is required for full-range analysis of the speaker's time-domain performance but then the measured tonal balance is incorrect because returning to the room, we hear the bass boosted by the presence of floors, walls and ceiling.

  • A dynamic tone-burst test is very useful for seeing what happens under short-duration stresses. 6 to 10 cycles of sine waves at various frequencies reveal a great many problems especially to locate a resonance. One can also see the effects of time-delays (phase shift) as those tone burst packets march back and forth across the face of the oscilloscope when they should remain in the same spot while different tones are applied.

  • Multiple-tone analysis shows great promise. This is a recently developed test method courtesy of high-power desktop computation. It can easily reveal a "dirty-sounding" driver that will sound hazy or confused on complex music. Using this new test method, we immediately know if a driver will perform poorly on complex music.

What do you say to those -- especially other loudspeaker designers -- who claim that time/phase coherence is unimportant or inaudible?
To call oneself a loudspeaker designer without valuing that all the sonic elements should arrive at the listener's ear in the same sequence as they were recorded leaves me speechless on the most fundamental level of my existence. A speaker designer is responsible for a major purchase in your life, a product that will be used every day. One makes this purchase in good faith that the designer understood all aspects of his job. You shouldn't be expected to discover any flaws afterwards. You rightfully expect he should have discovered and fixed any flaws before the product ever went to market. That's his job at least as the lead engineer.

He is also being paid to create new designs - paid to be a research scientist. This means he applies all of the techniques of his science, becoming familiar with all available research by examining it for good information, by learning why some of it has been superseded by newer insights, and then to design, conduct and analyse experiments. This is where his job demands the sternest discipline. Any problem must first be well-defined. If it is not, then the tools of science are useless and so is all the research by others.

If the designer failed to do a thorough job, the next opportunity for any checks and balances to occur is when professional reviewers put his speakers through their paces. Reviewers are self-declared watchdogs acting on behalf of the public interest. But who certifies reviewers? If reviewers don't know what they should be looking for, then the public interest suffers even more. In our culture, we've been trained to believe that the press is an investigative profession, one that delights in uncovering and unturning from every angle to report a complete story. Investigative journalists possess a defined body of study at a university that ends with a degree. However, audio reviewers are not really the same as the people who write and report the nightly news or serve the morning newspaper.

Soon that leads us to the last possible opportunity of expertise, the last place where there might be any hope: The retailer down the street. How can he prove to you that he knows what he's doing? Is there an independent body that checks his expertise? The checks and balances that are present in every other system in our culture are woefully missing in this industry. Is it any wonder that to most designers, time/phase coherence is unimportant or inaudible? It's accepted because most don't know any better. There is another way to explain this problem. Let's use some analogies:
  • Finding that your architect didn't understand square until after you've moved in.
  • Entering a contract drawn up by your attorney only to discover he was best at criminal law.
  • Realizing that your personal physician never thought blood pressure was important.
  • The automotive engineer who selectively forgot to tell the marketing department that the new SUV he designed will roll at the slightest provocation.

Then there is the good old visual analogy of the ghost in the television set. Remember what that looked like before cable and satellite? You got up, adjusted the antenna as best you could and continued to watch your show. At least you knew that the picture quality was horrible. You could see that because you could compare it to what you knew life looked like outside. Maybe you decided to take action. You called the store where you bought that television but were told, "Don't watch that station. There's nothing wrong with your television. It just reveals the flaws in that particular signal. After all, you bought the best television according to us and all the magazines that reviewed it!"

You then called the television manufacturer. You heard from them. "Like your retailer, we don't think it's your set. It must be the signal." You e-mailed the editor of a magazine who lauded that particular model only to read in his response. "Your problem must be with the station's signal." You called the station only to be told, "We send out a good signal certified by an FCC-licensed engineer."

Who do you hold accountable in this situation? The manufacturer, their designer, that retailer or the magazine? It's not likely to be the broadcast engineer. He went to university for that specific degree and then had to pass the FCC tests to get licensed. Further, the FCC tests were developed with decades of input from the leading broadcast engineers and the research departments of our top universities and companies like Bell Labs and RCA. The architect, attorney, physician, automotive engineer and broadcast engineer all expect the public to trust them because they passed the stringent requirements in order to become certified and thus hired. That certificate is also how the public holds them responsible and accountable. It's a two-way street.

But we have no watchdog -- no checks, balanced and formal requirements -- in home audio. Under these circumstances, it's a one-way street. This soon turns into a free-for-all as more manufactures crop up to meet demand. And it gets easier to lie to the consumer about something important like time/phase coherence in loudspeaker design. What has our culture demanded from corporate executives just within the past 10 or so years? Accountability. If we applied it to all of the home audio industry, how many designers would be fired or top executives jailed for perpetuating fraud?

Each one of us is a consumer. I dare say that each of us has encountered a problem that was utterly frustrating to solve whether with a government agency or business. Even the Internal Revenue Service was forced to change and become more responsive a few years ago after decades of outcries from citizens. However, with a product or service, it's too easy to give up and buy from another company or service provider. This fact of life well serves a host of agendas in the home audio industry, too.

So, what do we do about it? That television designer obviously did not go to a specialty university (but could have). A speaker designer doesn't even have that choice and no one recognizes the impact, especially those who should know first - CEO, the marketeers, the reviewers and the retailers. As long as their agendas are being met and as long as there are no checks and balances, they have no pressing reason to hold the designer accountable.

There is no defined path of education at any college or university for loudspeaker designers. Thus, every human being on the planet is truly at the mercy of poor speaker design. Think of the scope of that statement. Speakers now permeate nearly every facet of our lives. Besides the lack of educational standards for a speaker designer, consider our global culture. Where do we teach anyone "how to hear" and "what to listen for" within our education systems? Are these areas even valued? Where do we learn how to listen so we recognize when we're not hearing everything as it should be? Time-coherent sound flows naturally through our body's systems like water flows through a stream. Since our brains don't have to work to process it, we're able to enjoy what we hear on each of our five levels of being. In what school are we taught this?

Janet Lynn -- our chief executive -- and I have recently created The Green Mountain Foundation, Inc. as our company's attempt to bring these issues to the world's attention. One of the first activities will be to work with an interested university to structure the needed education pathway for speaker designers. Another will be to educate the public regarding the art of hearing. These initiatives are only the beginning of what needs to be done. Just as we spend so many years sleeping during our lifetimes, we probably spend even more time listening to music and movies. Just as we value a restful night's sleep and search for a comfortable bed, Janet and I agree that it's time to value our listening experiences in the same way that Hollywood has taught us to value our visual experiences.

Give examples of what a listener should look for when auditioning conventional loudspeakers, particularly with respect to timing and phase problems.
Always close your eyes to become a better listener and always remove any eye wear. The most important thing anyone can do when auditioning a speaker is to play a very wide range of music, even music that you do not normally play.

First, get those speakers away from reflective surfaces in a showroom. Then play several vocal recordings, male and female solos, then some duos and trios. We all know how real voices sound. Do those sound artificial such as pinched, lispy, in-your-face, boxy, mechanical, painful, chesty, thin or uninvolving? Does each and every voice, no matter the recording, have the snap and breath and clarity that you expect from someone singing two meters in front of you? Listen to the clarity, tonal balance and image of each voice as you stand up and then move around.

Move on to an acoustic guitar, a solo string bass, a single violin, then massed strings, large choral groups, bluegrass, a hot trumpet solo, then a saxophone, a piano, and a cello. Do all of those sound right or are some wrong - painful, piercing, muted, remote or again, musically uninvolving?

When a speaker has phase shift (a lack of time coherence), the first thing I notice is that the image has no depth especially in the tone ranges around each crossover point. Next, I hear how the tonal balance spanning each crossover range is not right, leading to the sound in a certain tone ranges to be piercing or boomy, laid-back or irritating at high volumes or "picky" on the guitar pick. Next, I hear that this speaker can be overly detailed and ultimately fatiguing. Many times, I hear the cymbals as loud as the lead instrument or voice, and/or presented just as far forward in the soundstage. No good engineer would mix a recording that way.

Each speaker design has different time delays in different frequency ranges. We hear the effects of those various phase errors in different ways at each frequency and at a different loudness. This is why it is so important to play an extreme range of music if you are to spot flaws then instead of six months later. More examples of what is heard are:

  • One type of phase shift between a mid and a tweeter will make marginal recordings unbearable and will make the loudspeaker require a certain amplifier to sound right. It will make certain piano notes jump out at you, sometimes "right into your ear". A different amount of phase shift in that range can have the opposite effect, making every recording very bland.

  • Phase shift between a woofer and midrange will collapse the concert-hall echo of an orchestra. It also keeps the wooden body of an acoustic guitar from sounding like the real thing. It can make the mid-bass boomy.

  • Phase shift between subwoofer and woofer usually is heard as room resonances and measures as if there were serious room problems. This is because the time delays a typical subwoofer crossover imposes are nearly the same time delays between the sound that travels over to nearby walls and returns to your ear when compared to the direct sound from the subwoofer and main woofers. Also, those crossovers do not let the subwoofer cone move at the same moment the principal woofers move and thus combined, they slow down a dynamic attack. A late-arriving sub also drags out the pace, rhythm and timing of music.

  • Play the speakers loud, then softly on several recordings. Phase shift is more unbearable when it is loud. Women are most sensitive to the shrieking of a speaker at high volumes, which is the sound heard when the spiked waveforms that define the tweeter's portion of the spectrum arrive sooner than the smoother voice range. When the "ess" and "tee" parts of the voice range arrive before the throat and chest sounds, they dominate our attention and affect the perceived tonal balance, the image, the musicality, and thus the message.
What can you tell us about the drivers, cabinet shape and material of the Callistos? Why cast marble and the shape?
Our cast marble is a unique recipe I developed over many years to be extraordinarily quiet and rigid. We modify this recipe for each of our models to fit specific requirements of the drivers and their frequency bands. To create the Callisto, eight different parts are molded, then several different adhesives are used to join those cabinet elements together and further damp the remaining internal crystal vibrations of this near-ceramic material. Although you can chip the corners, overall this cabinet is not fragile. You have to hit the body of the marble hard with a hammer to dent and eventually shatter it. This is a dense material so the weight of the Callistos can be important when deciding where to place them: approximately 56lbs (25kg) each.

Casting permits us to manufacture shapes that are best for dispersion of sound throughout the room. The shape of the Callisto was mathematically arrived at to avoid creating strong reflections in any particular direction or at any particular frequency. Its profile constantly curves in any direction including its rear panel (the smooth curves make a Callisto difficult to photograph).

The Callisto drivers are described in detail on our website but I will say here that they are extremely linear in every meaning of that word before I apply any crossover circuitry. The drivers in all our models are each burned-in for 24 hours, then individually tested against their reference drivers and then matched to +/- 0.25dB, creating a stereo pair of tweeters, mids or woofers. Those values are recorded so if a customer ever has a problem, we can send out a matching replacement driver.

In the Callisto, the tweeter is mechanically damped in its own sealed cast-marble chamber, which helps its clarity enormously. To my knowledge, this has not been done before.

The Callisto's twin bass ports are placed underneath to pressurize the listening room more uniformly in all directions. How they aerodynamically pick up and release the pressure behind the woofer is also nearly ideal. The stiffness and the airtight nature (when compared to wood) of the cast marble contribute to the bass response along with the naturally low distortion from its woofer, which is an underhung voice-coil design to reduces the distortions typical of small woofers.

The Callisto's crossover circuit has only six parts: an inductor of Litz wire wound for us by Solen in Canada as the only crossover component between the amplifier and the woofer; and a single SonicCap on the Morel tweeter. Then there is a voice-coil Zobel network for each driver. Internal wire is by Audio Magic on the woofer and from Jena Labs on the tweeter, with Marigo Audio's "Fusion" solder and Vampire Wire brass binding posts. There is no circuit board. The Callisto is not available as a bi-wired design because it does not change the sound very much for the money invested in the extra wire and because there is no room on the back for the extra terminals.

For the best sound, it is very important to adjust the rear spikes on the marble base so that the cabinet doesn't exhibit even the slightest corner-to-corner rocking motion