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In Reply to: RE: Believing in belief. posted by caspian@peak.org on September 11, 2009 at 12:42:40
hierarchy to audio tweaks.
Many tweaks induce relatively small changes in a system and if your system is not corrected for larger errors, the smaller ones may not be audible at all. The analogy I like to make is that if you start off with muddy water, no matter how much sugar and lemon you add, the taste will still be bad.
The most important aspect to any tweaking is to achieve a relative phase and time alignment of your speaker system. If you an not hear changes in signal polarity in your system, then something is very wrong. Those other factors must be corrected prior to performing any other tweaks because a system out of time and polarity alignment will smear rather than reveal the detail which is possible.
Achieving such a fundamental change, IMHO, means often recalibrating an entire system, something which many listeners would rather not do, because of the time and cost involved. It is important that the fundamental set us be attended to or else, the listener is apt to simply spend too much time and money working around these faults.
I, for one, would not recommend Mpingo discs or crystals on speaker system where drivers are out of polarity to each other. I have seen this attempted and the results are mixed: somethings get better, some things get worse, and the net conclusion is that it is a draw.
I specifically mention the polarity issue because after 20+ years of attending CES, I have rarely (only once, as a matter of fact) met any exhibitor or reviewer who seemed to be sensitive to polarity issues. I have in speaker designer's rooms and asked them to reverse polarity of the speakers ( easy to do with some CD players or DAC's ans most were surprised that 1.) I could detect a difference in sound without actually making a comparison, and 2.) that any polarity changes were actually audible.
Therein lies an important issue. If you are spending thousands of dollars to achieve "realistic, live" sound, we have to address fundamental issues. If such issues are not addressed, the mistake is carried forth and you end up "treating" a symptom, not necessary effecting a cure.
It would be a grave error to condemn what others hear without being aware of shortcomings within your own system first. I do know know what your personal system comprises of, so please do not take my comments personally. But adding a big carburetor to a stock four banger Pinto is not going to make it into a super muscle car. The same applies to many audio tweaks.
Stu
Follow Ups:
. . . is one of those "iffy" areas of perception. It has been proven in blind tests that a small percentage of the population (mostly professional musicians, with perfect pitch for what that's worth) CAN consistently hear the difference between normal and reverse polarity, but only with certain instruments like trumpet and chimes. The majority of people can't ever hear the difference, and a few can hear it sometimes but not always--possibly depending upon the resolution of the playback system.
You can easily configure your system for correct polarity, if you know which components do and do not invert phase. For instance, if your source component is known to output the signal in correct phase, but your pre-amp inverts phase, and your power-amp inverts it again, you know to hook up your speakers to the amp in "normal" phase (+ to +, - to -). But you're still at the mercy of your recordings, which may or may not be in correct polarity. In the case of multitracked recordings, some instruments and voices may be in correct polarity and others reversed.
There is a 50% chance any selected system will out of phase (polarity) for a randomly selected disc.
Of course ! Mathematically it it either in absolute polarity or not, hence the 50% deduction. That being said there are production values which may alter the polarity of the final recordings. I pointed out the example of the Commitments. An analysis of Phil Spector's Wall of Sound concept also reveals that he places the background instrumentals in inverted polarity and the singers in correct polarity, so where does that leave your statement?
The 50% probability does not apply, but an understanding of the effects and the cure is important for the listener to understand. Your statement betrays an listener who does not hear inversion. That as I previously posted is not uncommon ( my statement that after attending 20+ years of CES exhibitions, I have rarely met any exhibitor who can readily hear inversion). That being said, when I have used the exhibitor's equipment and demonstrated the difference, most could hear the sonic change. I distinctly remember one designer saying to me that while he was familiar with the concept and theory he had never bothered to actually play with the absolute polarity, although he was using a CD player with a digital polarity switch.
Many listeners fall into the same trap. They know all about the theory, and the possible ramifications, but neglect the most important part, and that is the actual comparison of a live instrument with their electronically recorded counterpart. While it is definitely easier to hear polarity with instruments which have a harder attack ( Brass and Woodwinds) the inversion of polarity also has an audible effect, however subtle, on the harmonic structures of even bowed instruments. If [phase and time alignment are not addressed, then the perpetual audiophile search for musical "accuracy" becomes a farce. Any tweaking becomes questionable because the results on a system with either mixed polarities or inverted polarities will, by its very nature, obscure many changes.
As for the 50% chance suggestion: consider this. Why does every Chesky CD chronologically issued before JD 63 exhibit correct polarity and every one after appear to be inverted (including their second test CD)? Why is it that the Mercury Living Presence CD reissues are phase correct when produced by Dennis Drake and become inverted after he is replaced? Why are most of my Philips and DDG LP's inverted, along with my Deccas?
In fact the RCA LP's recorded for them by Decca (Faust, Witches Brew, etc) are consistently inverted in polarity compared to the 1s versions of the recordings they made in the US.
Why is that the Hales Revelation series of speakers have their midrange inverted in polarity to the other drivers, as well as the Alon speakers? Why is this deliberate design choice so common (oh, I know the reasons given: the inversion produces a smother sine wave plot over the range of the driver since the inversion induces cancellation at the crossover overlaps creating what is heard as a steeper roll off slope). The technology is here and the means to make phase and time coherent speakers has long been availble. The one factor which holds back this development is that the listeners, both reviewer and the lay person, have not been made aware of the issue. This allows confusion to reign in the market place and a concerted push towards a standardized ideal is simply obfuscated.
Stu
I can hear, and I claim no special ability, differences in absolute polarity with even a $300 stereo receiver (HK) and a pair of $400 speakers (Sonance 622C), since my speakers are relatively phase and time aligned ( not perfect but close enough). Modern commercial recordings routinely mix polarity in order to achieve certain sound effects.
The question is if you do not "hear" such effects then certain tweaks will have little auditory benefit. Using an excuse that the majority of listeners can not hear the difference would be akin to marketing a water downed wine simply because the majority of the population can not tell the difference anyway.
In my years of running an audio store, education leads to recognition, but few are willing to undergo the education. Some of my regular customers, without perfect pitch at all, can quite easily recognize absolute polarity issues, but the problem, IMHO, is that many speaker designs employ driver assemblies with no semblance with time and phase regularities. One need only glance at the impulse tests given by Stereophile magazine to realize that, and that alteration of time constants is absolutely not what happens in real life.
Again, I reiterate: if your system does not have transducers with relatively time and phase aligned drivers, the "search" or "quest" for perfect sound is one doomed to failure.
As such, mixed polarity recordings abound, simply because listeners are too confused or lazy to comprehend the issue. For pop recordings absolute polarity is often used, as earlier stated, for sound effects. If you want an ethereal effect, invert the polarity. If you are singing a duet and the featured singer may not be as good as the partner invert the voice of the partner so that it smears the diction. A good example is the movie "The Commitments". The recently re released Director's cut, includes the director's comment that in order to make the singer sound really good, the polarity of the background singers and instrumentals were inverted to make his voice stand out.
However, the lack of knowledge of such effects exacerbates the problem. Producers use inversion even for orchestral music and classical recordings which shouldn't have to employ such "tricks". It also leads to listeners going on a absurd "quest" in search of the perfect recording and playback equipment.
The best example is the pronouncement of The Absolute Sound's editor claiming that the Canadian version of the Holly Cole Trio's "Don't Smoke in Bed" Cd was superior to the American. The trio has the piano in one polarity and the voice and bass in another. The Canadian version is simply reversed.
But again look at the impulse test results in Stereophile. The woofers are often many milliseconds behind the tweeters and often out of polarity. Do you see the magazine reviewers making any fuss about the issue? Most utter inane banalities on the quality of the sound, but are not really searching for constructive criticism. A speaker with a woofer retarded in time is often described as having big bass, simply because the bass notes stick out.
Some will claim that it can not be achieved, to which I simply point out that even the cheaper Vandersteen speakers achieve relatively accurate time and polarity alignment (not saying they are perfect as they have issues of their own).
Sorry I can not be an apologist for the general listener. If you search for "accurate" sound and spend thousands and still can not achieve it, then you are deserving for not educating yourself further.
Stu
"But again look at the impulse test results in Stereophile. The woofers are often many milliseconds behind the tweeters and often out of polarity.
Some will claim that it can not be achieved, to which I simply point out that even the cheaper Vandersteen speakers achieve relatively accurate time and polarity alignment (not saying they are perfect as they have issues of their own)."
Time and phase alignment (not the same thing) are noble goals, that some multi-way speaker designers strive for even at the cost of other serious compromises. The usual strategies -- stepped or tilted-back baffles, combined with first order electrical filters (as in Thiel and Vandersteen) -- may result in a pretty impulse response, but ONLY on a very narrowly defined vertical design axis. Raise or lower the measurement mic (or your head) by a couple of centimeters, and watch (hear) that beautiful impulse response go to hell. Add to this the lobing in the vertical polar response, typical of shallow crossovers, and you will measure/hear response dips around the crossover frequency, caused by phase cancellation, just a little bit above or below the primary lobe of the vertical design axis. (The shallow highpass slope may also allow too much energy to reach the tweeter below crossover frequency, resulting in audible distortion even at moderately loud SPLs).
These are inherent problems with ALL multiway speakers where there is vertical and horizontal separation between the drivers -- particularly mid and tweeter, where wavelengths are quite short in the crossover region. A coaxial mid/tweeter assembly is a better solution, and has been under constant refinement for years. The new Thiel unit, where the flat midrange ring radiator does not horn-load the tweeter, looks quite promising. Distance between woofer and midrange matters less, since the wavelengths around crossover frequency are so much longer. The multi-axial Cabasse "eyeball" drivers eliminate even this separation.
Even so, a perfect impulse response is likely ever to be seen ONLY with single driver speakers, be they dynamic or planar.
Phase tracking between drivers in a multiway system is a separate, but related issue. Look at the phase vs. frequency trace of ANY speaker driver made, and you will see that the phase goes through several 360 degree rotations over the operating range of the driver. When you're crossing one driver to another, the trick is to get the two phase responses to line up through the crossover region. Generally speaking, if you get excellent phase tracking, you will get a ruler-flat summation in the frequency response through the crossover region, and vice-versa. But the SYSTEM phase will still rotate with rising frequency. So the absolute phase of the speaker's acoustical output will still only match that of the electrical input signal at certain frequencies.
It's all compromise, and there's no free lunch.
Do you hear polarity inversions?
It is fine to know the theory (which I am quite familiar with, BTW), but do you hear inversion and its issues? I owned a pair of Martin Logan Quests ( and previously had Sequels and the CLS, and was plagued by the fact that their woofers are inverted to the panels. Being bi wireable, that was a simply issue to resolve. Strangely, although one would expect a huge hump in the crossover region where the two drivers overlap, there was little to annoy me and the timing alignment more than made up for any hump that may have happened on occasion.
Phase is indeed constantly changing depending on the impedances of the voice coils and such, but I find that so long as it remains within 90 degrees or so relative to each other, the sound emitted is far more coherent than one which starts off 180 degrees apart. I do not pretend to be an apologist for the various speaker and crossover designs. It has been my observation that too many are overly enamored of the results printed out from their computer and too little emphasis is placed on the the resolving transducers on the sides of your head.
Stu
PS look at the impulse test for the Vandersteen Quattro and then look at the results of the Thiel 3.7: remarkably similar and yet one uses a simpler driver design. The problem can be addressed and resolved: listeners have to train themselves to be aware of the issue.
Hiya Stu:
With the normal/reverse polarity tracks on the Chesky test disc, I can hear some difference with headphones, though in a blind AB test I probably couldn't readily identify which is which. I can also hear some difference on the little speakers I built last year for outdoor listening, but only consistently so outdoors, when the neighborhood is quiet. Indoors, despite a reasonably well-treated and acoustically "dead" room, not so consistently. Room effects seem to overwhelm the subtle difference.
Like you, I prefer speakers where all the drivers are connected in positive polarity. The only situation where drivers NEED to be connected in reverse polarity is with a true 2nd (or 6th) order crossover: in that case, the filter-induced 180 degree phase shift necessitates reverse electrical polarity in order for the drivers to be acoustically in phase and sum flat AT crossover frequency. Put both drivers in positive polarity and you will get a huge response suckout, NOT a hump. Of course, you get a couple of octaves out, either side of xo, and they're out of phase, which means higher harmonics will be inverted 180 degrees relative to their fundamentals. Not really a recipe for natural sound.
With good, smooth, wideband drivers, I can usually achieve a quasi-LR4 response with a 1st order electrical filter plus Zobel on the midbass, 2nd order electrical plus L-padding on the tweeter, both down -6dB at the chosen crosspoint, AND keep both drivers in positive polarity. The slightly "relaxed" lowpass electrical transfer function somewhat alleviates the time-misalignment of having the drivers flush-mounted on a vertical baffle. It's also quite easy to work in baffle step compensation with this arrangement: you calculate an oversized series inductor on the lowpass that will be down -3dB at the frequency where the baffle diffraction step is up +3dB, and then figure your crosspoint to the tweeter about two octaves (-12dB down from the midbass driver's reference sensitivity) above that. Quite easy to model, even with basic design software.
BTW, do you know of a published impulse response on the Dahlquist DQ-10s? Those, to my ears, are among the most "natural" sounding speakers I've ever heard, other than Quad ESLs. John Dahlquist obviously put a great deal of effort into the driver spacing on those, apparently trying to optimize time & phase coherency.
Don't know of any such test results o for the DQ-10.
One factor which distresses me about the DQ-10s is the non symmetrical spacing of the the individual drivers and the fact that the speaker is not made in mirrored pairs. I find that speaker symmetry is quite important for my ears. I particularly dislike when tweeters are made off set to the other drivers. I find that the propagation of the sound field will be symmetrical about a line drawn through the tweeter and midrange drivers. Thus if the tweeters are mounted inboard that line converges in the center between the speakers and thus throws a significantly lower sound stage. If mounted outboard, it throws a soundstage that is high in the middle but droops at the periphery outboard of the the speakers.
The interaction of the drivers among themselves also creates a large amount of distortion through their interaction Mounting the drivers in a single line column vertically seems to reduce the inter driver action.
Incidentally it is quite easy to demonstrate this interaction and the issues it creates. I believe the bulk of the issue comes from cancellation between the drivers, when the same wavelengths meet 180 degrees apart on the speaker baffle. That's when any crossover frequency overlap result in cancellation, generally. You can easily hear this feature and manipulate it to your advantage by creating a small "dam" between drivers on the baffle about half way between the drivers. A length of putty about a 1/8th of an inch high is all you need. This will prevent the air flow diametrically opposed from interacting and you will hear a noticeable rise in the area where the crossover frequencies overlap. By moving this dam closer towards one driver you can increase or decrease the dispersion of the air flow from that drivers and thus effect a user controllable tone control of sorts.
Stu
"One factor which distresses me about the DQ-10s is the non symmetrical spacing of the the individual drivers and the fact that the speaker is not made in mirrored pairs."
Yeah, that driver layout IS kinda wacky, but in the design iteration I have (and I believe there were several?), the tweeter is mounted on a recessed (time-aligned?) baffle directly above the upper (dome) mid. The lower (cone) mid is over to the side, about a foot away, however. At the crossover frequency between the lower and upper mids (around 800Hz?), the wavelength is just about long enough to make that separation inoffensive. But any lobing in the polar response between the two drivers WILL occur in the horizontal rather than the vertical plane. The lower mid operates in "muffled dipole" mode, with a thick felt pad over the back, which complicates things further. The crossover frequency between woofer and lower mid (around 250Hz?) is presumably low enough that the slight horizontal offset (about 30 degrees off vertical) won't matter. The horrid piezo superscreechers were mounted on the corner of the lower mids' baffles -- who knows why? -- but I got rid of those, along with their entire leg of the crossover network, and mounted some old JVC ribbons, crossed in at 12.5kHz, to the side of the dome tweeters. (Thanks, Dave Elledge, for both the ribbons and the crossover component values). I would have preferred to mount them above, for the good reasons you cite, but they wouldn't fit behind the grill that way. And these things are boot-oogly without the grills -- naked Vandersteens are Miss America by comparison. Supposedly the ScanSpeak 9300 is a drop-in replacement for the old Phillips tweet, and precludes the need for a supertweet, but that mod is down the road yet.
I do need to swap the side-by-side baffles around on one of the speakers, to mirror-image them, but that's another "down the road" project. Involves replacing -- or splicing -- a whole lot of wires. I measured and sketched out all I would have to do, and got a serious attack of the dont-wannas. I did put felt anti-diffraction rings on the tweeter faceplates, and felt blocks on the edges of the midrange baffles (similar to your suggestion with the putty). I also replaced all the old crossover NPE caps with poly-film types, of higher voltage rating and tighter tolerance.
But as weird as they are (and as many of the truly innovative vintage designs were), I still seriously LOVE the sound of these speakers. Yeah they're inefficient low-impedance power hogs, but DAMMIT they draw me into the music! I'm an acoustic musician, and know well the live, unamplified, nearfield sound of fiddles, guitars, banjos, flutes, mandolins, string basses, pianos, etc., from many a gig and informal session. The DQ10s reproduce the sound of these (and presumably other) instruments, from good recordings, with remarkable ease and naturalness.
Also, they WERE among the first "audiophile" speakers that got people rhinking about imaging and soundstaging. I suspect, as you suggest, that the weird driver layout adds it's own effects to the perceived soundstage, but they nonetheless sort out all the parts in busy arrangements rather well. Perhaps I'm biased by all the work I put into restoring these, after getting them for nearly free, but I'm extremely happy with them.
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