Rockport Sirius III
If you love vinyl, you want this turntable.
This is a whole new kind of turntable for Rockport. This is a whole new kind of turntable for anybody. This is a whole new kind of turntable, period.
The most essential job for a turntable is to spin your record at a constant speed. Really constant. This is the first turntable to do it right. Really right.
In order to fully understand what this turntable does right, we first need to candidly reveal all the things that other turntables, in contrast, do wrong. Candid revelation requires detailed analysis, so that we don't gullibly swallow the sales hype of past turntables, whose broad generalizations gloss over the details which constitute that little thing called the truth. We need to penetrate beneath the surface gloss of sales hype.
But every cogent analysis, even a detailed one, should be logically organized, and based on a simple conceptual foundation as a key starting point.
Our conceptual foundation, our key starting point, is simple. Speed. Speed is the last great hurdle in turntable design, and no one has really conquered this hurdle. Until now.
Why is speed so important? As you know, the primary job of any record player, including turntable, arm, and cartridge, is to accurately reproduce the waveform of the music as it was originally recorded onto a vinyl record.
But how exactly is this job divided up among the turntable, arm, and cartridge? Most people would say that the cartridge has the job of reproducing the entire music waveform, and that the turntable and arm have lesser passive roles, merely responsible for being stable platforms for the record and cartridge, so the cartridge can do all the active work, reading the entire music waveform from the record.
That's wrong. The cartridge does not read the entire music waveform from the record. It can't.
Why not? Because the vinyl record contains only half of the music waveform.
Where then does the other half of the music waveform come from? It comes from the turntable. That's right. The turntable is fully responsible for actively supplying half of the music waveform, and the other half comes from the cartridge.
This puts turntables in a whole new light. If a turntable's job is to actively supply half of your music's waveform, then it had better be doing its job right, otherwise your music will obviously and dramatically suffer -- to an extent you wouldn't have imagined when you thought that music's entire waveform came from the cartridge.
What do we mean by saying that half the music waveform comes from the turntable? You know that music's waveform can be plotted on a graph or on an oscilloscope. The graph of a music waveform has two axes, as do most common graphs. The vertical axis represents amplitude, and the horizontal axis represents time. The music waveform needs both these axes to exist, since it is a two dimensional entity in nature. If one dimensional axis or the other were somehow missing, there couldn't be any music waveform, and there couldn't be any music. Music itself is a time bound art form, and its existence depends on the two dimensions of time and amplitude as surely as a sculpture depends on three spatial dimensions (but not on time in the case of static sculpture).
In a record player, the vertical amplitude axis of the music waveform comes entirely from the cartridge. But the horizontal time axis of this music waveform comes entirely from the turntable.
The vinyl record groove contains an analog of the vertical amplitude axis variations of the music waveform. These amplitude variations are laid out along the length of a long linear groove (that happens to spiral). These amplitude variations are laid out along this groove length with the assumption (repeat: ASSUMPTION) that the horizontal time axis for the music waveform will later be supplied by a turntable rotating the vinyl disc at a constant speed. But the time axis for the musical waveform is not (repeat: NOT) encoded into the vinyl disc itself. The disc groove contains only the amplitude axis variations, so it only contains half the information needed to recreate or plot the original music waveform on a graph. The disc groove contains not the slightest clue about what the horizontal time axis of the music waveform is supposed to be (as you know if you've ever played back a 45 rpm LP at 33 rpm). There are no guiding ticks imprinted into the groove at a constant timing rate (say 1 per second). There are no discrete CD pits to guide the turntable platter to spin at the correct rpm.
It's like a gentleman's agreement. The record manufacturer actually gives you only half the music waveform in the groove, for your cartridge to read, namely the vertical amplitude axis. You agree to supply the other required half of the music waveform, the horizontal time axis, by agreeing to employ an accurate turntable to play back the record manufacturer's disc. The turntable that you chose to employ literally supplies the time axis half of the music waveform, while your cartridge reads the amplitude variation half (and only that) furnished by the record manufacturer, as the groove is passed underfoot by your turntable recreating the time axis half on the fly.
Consider the following analogy. Imagine first that you want to draw a music waveform, like the ones you've seen in previous IAR articles. Draw it on a square piece of graph paper. Note that you can freely move your hand in two dimensions on the graph paper, so you can simultaneously draw both the varying amplitude (height) and progressing time (horizontal axis) of the waveform on the graph paper. Next, imagine that you're doing the same thing, but you've turned the piece of graph paper sideways, so that your wrist moves from side to side (instead of up and down) as you're charting the waveform's amplitude variations.
Now, imagine that you can only move your wrist from side to side, and can't move your hand up and down at all. Your hand holding the drawing stylus has now become just like a phono cartridge holding a stylus that can only read the side to side variations in a record groove. Your hand holding the waveform drawing stylus is mounted on your arm, the same way that a cartridge holding the waveform reading stylus is mounted on the pickup arm of the record player.
If you were to try drawing a music waveform, while limiting your hand to only this side to side motion, you couldn't do it. There would have to be a further mechanism for moving the drawing stylus in your hand along the time axis of the graph paper where you want to draw the complete music waveform. You could for example rely on a strip chart recorder, which could dispense the graph paper in strip form at a fixed time rate (you've probably seen strip chart recorders in the form of earthquake recorders, where the side to side needle motion indicates earthquake amplitude, on a steadily unrolling strip of graph paper; if you're unacquainted with this, imagine a roll of toilet paper unrolling at a steady rate). The strip chart recorder makes the graph paper move along under your hand at a constant speed, thus creating a steady time axis for the waveform you wish to draw. And the strip chart literally creates this time axis. Your hand is limited to reproducing (accurately we hope) only the amplitude axis of the music waveform, since you are now limited to side to side motion.
That's exactly what a turntable does. It literally creates the time axis half of your music waveform, while the cartridge, which is restricted to side to side motion, reproduces (accurately we hope) the amplitude information that the grove contains.
What happens if the turntable speed is inaccurate in any way (momentarily or over the long run)? Let's go back to the analogy of your drawing the music waveform on a strip chart recorder. If the strip chart recorder fails to move the paper under your drawing hand at a precisely constant speed (and the correct constant speed), what would happen? The waveform you drew of the music would be distorted! For example, your hand might move side to side to the correct amplitude position for a musical peak, but if the strip chart recorder moved the chart paper a bit too fast, then your hand would draw that musical peak at the correct amplitude but in the wrong location on the time axis. The peak would come too soon on the resulting graph you drew on paper of the music waveform. How would this be a distortion? The portion of the music waveform preceding the peak would be compressed or squashed, into a too short time period. When you took your graph paper out and looked at the music waveform as a whole that you had just drawn, it would not be correct. It would be squashed horizontally. It would be a distorted, inaccurate version of the music waveform, as surely as if you were to have drawn the incorrect amplitude by moving your hand side to side in an inaccurate manner.
The key point here is that an error in the time axis would produce a distorted error in the correct shape of the music waveform, as surely as if your hand were to have erred in a distorted way in reproducing the correct amplitude swings of the music waveform. We give a great deal of attention to making sure that cartridges are accurate reproducers, so that they correctly read the side to side swings of the record groove that furnish the amplitude information about the music waveform, and thereby do not distort the music waveform themselves. But that's literally only half the story. We should also devote equal attention to making sure that the turntable accurately furnishes the time axis half of the music waveform. If we don't, then the final resulting music waveform will be distorted, as surely as if the cartridge were contributing unwanted distortion by inaccurately reading the amplitude axis half in its side to side swings.
The lesson is clear. You could buy the world's most expensive, most perfect cartridge, that exhibited perfect accuracy in reproducing the amplitude half of the music waveform from its side to side swings in tracing the record groove. But, unless your turntable is perfect in creating the time axis half of the music waveform, the final music waveform you hear will be distorted. The right amplitude played at the wrong time will distort the music waveform as surely as the wrong amplitude played at the right time.
We discussed this same lesson in IAR Hotline, in conjunction with digital. We saw there that jitter (also a simple timing error) distorted the final music signal from a digital system, as surely as if some bits of resolution had been lost in decoding the amplitude of the music waveform. We saw that jitter, though a simple timing error, did not merely produce timing errors (such as frequency or pitch variations) in the final music signal, but instead actually introduced distortion of the music waveform, especially modulation distortion, and in particular frequency modulation distortion. This distortion would be apt to make music sound fuzzy, defocused, smeared, dirty, grundgy, frazzled, etc., while degrading transparency, stereo imaging, clean purity, etc.
In the past, most people have assumed that any speed errors in a turntable would be audible only as pitch errors, making the music sound off pitch or at worst slightly wobbly in pitch. But turntable speed errors also have other sonic consequences, which are far more pernicious. By playing the right amplitude at the wrong time, turntable speed errors create a distorted music waveform, even if the rest of your system were to be perfect. Indeed, as cartridges get better and better, becoming far cleaner and more accurate in tracking the amplitude half of the music waveform from the groove, and as the rest of our system chain continues to become at once cleaner and more revealing of everything (including not only the music but also distortions from our program sources), the waveform distortions due to turntable speed errors become more noticeable, and become the last remaining hurdle of the state of the art.
Moreover, the distortions due to turntable speed errors could actually be more pernicious than those due to cartridge imperfections. Cartridge distortions tend to be amplitude distortions, thus producing harmonic distortion (some of which is actually psychoacoustically benign) and amplitude modulation distortion (due to the fact that music, being complex, contains many frequencies at once). But turntable speed errors predominantly produce a different kind of modulation distortion, called frequency modulation distortion. Pioneering work by Paul Klipsch 50 years ago already found that this FM distortion is more pernicious than AM distortion, being more audible and more objectionable in smaller amounts.
If FM distortion is present in very large amounts, and with certain slow modulating rates, it might be heard predominantly as pitch variations, or wow and flutter. But FM distortion in much lesser amounts can still create sidebands, distortion byproducts, around each musical note. These unwanted sidebands could make the music sound fuzzy, defocused, smeared, dirty, grundgy, frazzled, etc., while degrading transparency, stereo imaging, clean purity, etc.
FM distortion from a turntable takes what should be a purely precise time line ordering and spacing of musical events, and instead applies a different time line, one which variously contracts and expands like the pleats of an accordion in motion. The waveform is distorted so that some musical peaks are too close together, while others are spaced too far apart; some waveform valleys are too wide, while others are too narrow; some peaks themselves are too wide, while others are too narrow. You can imagine what this might for example do to the sound of a pure, clean, simple trumpet note. A trumpet note basically looks like a series of identical sharp spikes, spaced apart from each other by the same exact time intervals. However, turntable FM distortion would make these spikes have different widths or thicknesses. The too thick spikes might sound darkly grundgy and garbled, while the too thin spikes might sound brightly frizzy or edgy. Thus, you'd already have a trumpet sound that is at once too grundgy and also too frizzy, with both dark and bright distortions, instead of a pure, clean, consistent musical note. Furthermore, turntable FM distortion would place some of these spikes too close together while others would be too far apart. This would probably make the trumpet note sound smeared, defocused, and closed in, with degraded intertransient silence, instead of sounding pure, clean, articulate, and open, with a black silent background. Incidentally, the same effect at lower frequencies, where a bass note depends on a repeating pattern for its sonic quality, could explain why some turntables (and CD transports with close in jitter sidebands) have problems playing bass notes with steady pace, timing, foot tapping rhythm, tight slam, etc.
A turntable with truly accurate speed could allow your music to sound more transparent, clean, pure, articulate, individualized, pristine, delicate, open, and airy, with better intertransient silence and better stereo imaging.
How can one make a turntable have more accurate speed? What's wrong with the speed accuracy of all other turntables to date?
We have basically had just two kinds of turntable drive systems over the years, rigid drive from a multipole motor and elastic drive.
Rigid drive has the disadvantage that it directly couples speed variations in the motor to the turntable platter. All multipole motors have speed variations. A typical turntable motor might have 24 poles. This configuration gives the motor 24 discrete power kicks per revolution of the motor. Between power kicks the motor just coasts, and thus slows down. Therefore, if the average speed of the motor is to be correct for a whole revolution, it has to speed up to faster than correct speed during each kick, to compensate for the speed it loses during each coast between kicks.
Remember the foot driven merry go round you played on as a kid? Every once in a while you'd reach down with your foot to give the merry go round another kick, to keep it going. The average speed of your merry go round was (by definition) between the higher speed you injected with each kick and the slower speed it coasted to that made you realize it needed another kick of speed added. That merry go round had significant speed variation, and so does a multipole motor, which works on the same principle. Incidentally, note that if you try to maintain the merry go round at some given average speed as a correct target speed (say 33 rpm), then the kick method is hopelessly inadequate. That's because over 99% of the time the merry go round will be going at some wrong speed, too fast or too slow, having either just been kicked to some higher than correct speed, or having coasted past the correct speed down to some slower speed before it gets the next kick. Indeed, the merry go round will be going at the correct speed only momentarily in passing, during each kick and coast cycle.
Likewise, turntables with rigid drive from multipole motors are almost never at the correct speed. They kick up above the correct speed and then coast down to below the correct speed. This kicking, cogging problem applies regardless of the particular rigid drive system, and regardless of the number of commonly used poles in the motor (2 to 24). For example, rigid drives with rubber puck reduction coupling have commonly used 2 or 4 pole motors rotating at 360 rpm, which works out to yielding about 22 or 43 kicks per revolution of the platter, while direct drive motors have commonly used 24 poles, which of course yields 24 kicks per revolution of the platter.
It's disconcerting to know that your turntable is actually almost never at the correct speed if it uses this kick and coast drive mechanism. Who wants the pitch of his music to be constantly shifting? But as discussed above, the sonic degradations from this mechanism reach far beyond shifting pitch. The kick and coast mechanism is operating at a basic repetition rate of about 13 Hz in a direct drive turntable with a 24 pole motor (about 24 Hz in a puck system with a 4 pole motor). This means that the kick and coast mechanism distorts your music, creating spurious FM distortion byproducts as sidebands, spaced 13 Hz (or 24 Hz) away from each and every musical note, from every musical nuance, that your record player is trying to reproduce from the disc. What's worse, there are also harmonics of these sidebands, since the kick and coast mechanism is not perfectly sinusoidal.
This is a very nasty picture of what a turntable can actively do wrong to mess up your sound. The turntable, far from being a passive carrier of the disc containing all the musical information, is totally responsible for creating the time axis for your musical waveform. And, if it fails to do this perfectly (by exhibiting speed irregularities), then it literally creates distortion byproducts that spring up like weeds amidst all your music. These distortion byproducts themselves sound dirty, and they also smear your musical information, filling in what should be a black background of intertransient silence between musical details, with the garbage of their added energy, and thereby degrading the individuation of each musical nuance. How can you enjoy the pure beauty of individual roses against a background of black earth when there are weeds sprouting up all around the roses, cluttering the
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