Hello Jean-Michel,
I don't know what to say because I've done a few designs, all of which are series XO, and I try to focus on overal system performance. During one design session, I tried a design that looked very good on analysis and measurements which had two drivers in opposite polarity, but when I listened to music, some instruments sounded right and some sounded like they were a bit muffled. Since these instruments had very distinct frequency ranges. I swapped the absolute polarity on the system, then I heard the instruments that originally sounded right then sounded a bit muffled, and vice versa; so I went to modify the design such that both drivers were connected with the same polarity, and the result was much better. After that experience, I just make it a rule to always design with drivers connected in the same polarity.
I don't know what to say because I've done a few designs, all of which are series XO, and I try to focus on overal system performance. During one design session, I tried a design that looked very good on analysis and measurements which had two drivers in opposite polarity, but when I listened to music, some instruments sounded right and some sounded like they were a bit muffled. Since these instruments had very distinct frequency ranges. I swapped the absolute polarity on the system, then I heard the instruments that originally sounded right then sounded a bit muffled, and vice versa; so I went to modify the design such that both drivers were connected with the same polarity, and the result was much better. After that experience, I just make it a rule to always design with drivers connected in the same polarity.
Thats a bit of a rash conclusion based on one casual test since your subjective results could be caused by a myriad of factors other than the crossover.
Originally Posted by john k...
... the best approach is to design a system to have good polar response ...
Actually - there is a strong point to achieve both goals – no need to stop half ways....
We want it all and we want (and even got) it now - felice me that is!
John's min phase concept is the key!
Michael
... the best approach is to design a system to have good polar response ...
Actually - there is a strong point to achieve both goals – no need to stop half ways....
We want it all and we want (and even got) it now - felice me that is!
John's min phase concept is the key!
Michael
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I don't think that is what I wrote and it is certainly not what I meant. There are numerous causal crossover filters which can achieve true linear phase aside from the 1st order pair. I won't list them because I believe most here are aware of them. Many of them can be achieved passively as well.
My interest in building such a system has waned because DSP provides a much more reasonable solution as it can not only address transient distortion due to the crossover, but also that associated with low frequency cut off of the system. And while I have been direct in my discussion of the approaches defined by Jean-Michel I am not in total disagreement that above a certain frequency time distortion becomes more difficult for listeners to identify. We would all agree that a system is grossly misaligned if we hear individual pulses form midrange and tweeter. This is purely a alignment issue and not necessarily related to transient "perfectness". I.e. a time aligned system with one driver inverted will be superior to a severely misaligned system with correct polarity.
Hello John,
No, in my method the first arrival time are not perfectly aligned as you erroneously say.
If you use my spreadsheet (the link of which has been given previously), you'll see that there is still a minor group delay difference between the bass and the HF.
See attached file: the comparison between a classical 3rd order Butterworth 2 ways with Fc 1kHz and the equivalent Le Cléac'h croossover.
The in "coincidence" curve is very near of the response curve indicating a very good in phase operation between the waves emitted by the 2 loudspeakers. (an horizontal "in coincidence" will indicate a perfect in phase operation of the 2 loudspeakers).
But look at the variation of the group delay (expressed in equivalent distance travelled at the speed sound) between the classical Butterworth and the Le Cleach: 72mm of varition for frequency <4000Hz for the Butterworth, 17mm of variation for the Le Cléac'h, indicating for that one an increased phase linearity.
Above 4kHz the phase of the tweeter is for sure progressively tending toward 180 degrees but this is inaudible IMHO.
About the very low frequency why one would care if his tweeter is not perfectly in phase at -40dB level or so, with the bass loudspeaker...!
It is far most important IMHO to consider the interval of frequency wher the 2 loudspeakers have a significant SPL and in that range, with the Le Cleac'h crossover the 2 loudspeakers operate with very low phase difference.
(BTW, I don't set up the crossover using square waves, I used pulse response and phase curves, group delay curves and CSD... square waves are given in the document because during discussion in French forum, many people asked me to give them in order to compare with published square waves ... )
Many people use my crossover in a 3 ways systems and my spreadsheet is devoted to 3 ways systems...
Best regards from Paris, France
Jean-Michel Le Cléac'h
No, in my method the first arrival time are not perfectly aligned as you erroneously say.
If you use my spreadsheet (the link of which has been given previously), you'll see that there is still a minor group delay difference between the bass and the HF.
See attached file: the comparison between a classical 3rd order Butterworth 2 ways with Fc 1kHz and the equivalent Le Cléac'h croossover.
The in "coincidence" curve is very near of the response curve indicating a very good in phase operation between the waves emitted by the 2 loudspeakers. (an horizontal "in coincidence" will indicate a perfect in phase operation of the 2 loudspeakers).
But look at the variation of the group delay (expressed in equivalent distance travelled at the speed sound) between the classical Butterworth and the Le Cleach: 72mm of varition for frequency <4000Hz for the Butterworth, 17mm of variation for the Le Cléac'h, indicating for that one an increased phase linearity.
Above 4kHz the phase of the tweeter is for sure progressively tending toward 180 degrees but this is inaudible IMHO.
About the very low frequency why one would care if his tweeter is not perfectly in phase at -40dB level or so, with the bass loudspeaker...!
It is far most important IMHO to consider the interval of frequency wher the 2 loudspeakers have a significant SPL and in that range, with the Le Cleac'h crossover the 2 loudspeakers operate with very low phase difference.
(BTW, I don't set up the crossover using square waves, I used pulse response and phase curves, group delay curves and CSD... square waves are given in the document because during discussion in French forum, many people asked me to give them in order to compare with published square waves ... )
Many people use my crossover in a 3 ways systems and my spreadsheet is devoted to 3 ways systems...
Best regards from Paris, France
Jean-Michel Le Cléac'h
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I don't want to use DSP to correct amplitude, just system phase response. If you look at the plost I posted a while back the system amplitude remained constant. Only phase was manipulated with DSP.
The idea being to make the impulse response as compact as possible, correct? (Hence good "transient response" and square wave behavior). If this is true then I entirely agree that one needs to have the system impulse response as compact as possible and that this impulse response should remain so over as large a frontal angle as possible. This has always been my goal. I have tried DSP before and found that its advantages were outweighed by its additional cost. But I don't bother with complex analysis on paper since in the end, with a waveguide, the waveguide is going to dominate the ability to achieve the end result and including it in an analysis, while very attractive, is analytically not reasonable.
I do have to admit to be attracted by the idea of using DSP at the very end just to clean up any phase and amplitude anomally that the passive design was not getting, but it would all come down to "bang for the buck". My experince with DSP has been that its not worth the cost (except in things like receivers and radios etc where it can do a hole lot of stuff at the same time.) Worth a try however.
Well, if I were doing a PHD thesis, I probably would spend more time to do a whole bunch of studies. Since only the XO changed, and the resulting effect was logical, I did not see much reason to dig deeper. What other factors could cause that?
Hello Songsc,
Polarity of a loudspeaker fed through a crossover (e.g. an "high-pass" crossover) is quite meaningless in itself, it only becomes important when the summation of 2 filtered loudspeakers is considered.
Let's consider a single crossover : a single high pass (+ a perfect loudspeaker) for example.
You have to remember that using conventional polynomial crossovers having an order larger than 2, a high-pass crossover will turn the phase within it's bandwith more than 180°. (Said in other form: we have frequencies at the output of the crossover for which the phase is + or -180° different of the phase at other frequencies).
Inverting the polarity will just add 180 degrees to the phase at every frequency, but the variation (rotation) of phase through the bandwith of the high pass crossover will still be there. So, considered in itself the polarity is quite meaningless.
When used in a 2 ways system (or more) the polarity inversion has to be performed sometimes on one loudspeaker in order that the wave it emits (at a given frequency inside the interval of frequency around the common cut-off of the LP and the HP) will be in phase with the wave emitted at the same frequency by the complementary loudspeaker (+ crossover). The perfect example of that is the 2nd order Linkwitz-Riley which needs a phase inversion of one of the 2 loudspeakers in order to have them operating in phase at every frequency around the common cut-off (f-6dB in that case).
Best regards from Paris, France
Jean-Michel Le Cléac'h
Polarity of a loudspeaker fed through a crossover (e.g. an "high-pass" crossover) is quite meaningless in itself, it only becomes important when the summation of 2 filtered loudspeakers is considered.
Let's consider a single crossover : a single high pass (+ a perfect loudspeaker) for example.
You have to remember that using conventional polynomial crossovers having an order larger than 2, a high-pass crossover will turn the phase within it's bandwith more than 180°. (Said in other form: we have frequencies at the output of the crossover for which the phase is + or -180° different of the phase at other frequencies).
Inverting the polarity will just add 180 degrees to the phase at every frequency, but the variation (rotation) of phase through the bandwith of the high pass crossover will still be there. So, considered in itself the polarity is quite meaningless.
When used in a 2 ways system (or more) the polarity inversion has to be performed sometimes on one loudspeaker in order that the wave it emits (at a given frequency inside the interval of frequency around the common cut-off of the LP and the HP) will be in phase with the wave emitted at the same frequency by the complementary loudspeaker (+ crossover). The perfect example of that is the 2nd order Linkwitz-Riley which needs a phase inversion of one of the 2 loudspeakers in order to have them operating in phase at every frequency around the common cut-off (f-6dB in that case).
Best regards from Paris, France
Jean-Michel Le Cléac'h
Hello Jean-Michel,
This point of view has been around for a long time, but I beleive in what I hear, and the relationship with design logic and data seems consistent. I have also demonstrated polarity effects on full range drivers to many people here as well. I was listening to a set of B&W 800D speakers once, and heard some irregularities, when I asked whether a crossover frequency was near the 4K region or not, sure thing it was. So I am merely sharing this experience about polarity. A simple test to do to test parallel filters only is to send music signal through the filters and sum them together. If the sum differs from the original, then the fidelity is not preserved. The diffmaker at the Praxis site can help check the difference.
Jean-Michel,
I don't know about 3-ways. Your argument is that everything 2 octaves above the x-o point is unimportant when you have a 2-way with 1k Hz x-0. With a 3-way that translates to everything 2 octaves above the woofer/mid crossover is unimportant. The thing is that any time a high pass filter is introduced, be it from the box alignment, the HP on the mid, or the HP on the tweeter, nonlinear phase is introduced. Also, at typical mid/woofer crossovers the drivers are acoustically closely spaced so polar response artifacts due to the crossover aren't generally an issue. I think, as Earl mentioned, you are looking too much at the characteristics of the crossover alone without considering the impact of other elements of the system.
And the required offset about 240/f in feet. So a 100 Hz crossover would require a 2.4 ft offset.
I don't know about 3-ways. Your argument is that everything 2 octaves above the x-o point is unimportant when you have a 2-way with 1k Hz x-0. With a 3-way that translates to everything 2 octaves above the woofer/mid crossover is unimportant. The thing is that any time a high pass filter is introduced, be it from the box alignment, the HP on the mid, or the HP on the tweeter, nonlinear phase is introduced. Also, at typical mid/woofer crossovers the drivers are acoustically closely spaced so polar response artifacts due to the crossover aren't generally an issue. I think, as Earl mentioned, you are looking too much at the characteristics of the crossover alone without considering the impact of other elements of the system.
And the required offset about 240/f in feet. So a 100 Hz crossover would require a 2.4 ft offset.
MJAO G098 - The Anagram
I have in fact constructed a passive 3-way OB in line with all the phase discussion voiced here: http://www.audiocircle.com/index.php?topic=65570.100 . The link is to the final crossover revision. Perhaps you have to read the thread from the beginning to get element details also. But why don't you all build this and stay happy for the rest of your life.
/Erling
I have in fact constructed a passive 3-way OB in line with all the phase discussion voiced here: http://www.audiocircle.com/index.php?topic=65570.100 . The link is to the final crossover revision. Perhaps you have to read the thread from the beginning to get element details also. But why don't you all build this and stay happy for the rest of your life.
/Erling
This is classic audiophile - obsessive focus on an insignificant detail while loosing sight of the bigger task of accurate audio reproduction. Everything must be taken within the context of its importance to the overall task.
Earl,
I don't think so as my design is a genuinly phase correct one which from the discussion here seems to be very rare.
Otherwise I was hoping that the irony should come through even in this discussion of matters of life and death, and so I read your answer also. Of course presentation should be as good as possible, and there will be more ways than one to achieve this.
For the moment I am listening to an oversimplified Emerald Physics clone consisting of two Eminence Alphas and a Vifa D27TG35-06 tweaked by cutting its back chamber off mounted in this same MJAO baffle. No waveguide but playing through SRC2496 and DCX2496 EQ this speaker presents itself with an authoritative statement I didn't think possible. So what shouldn't happen with the PE waveguide and proper positioning for time alignment: http://www.audiocircle.com/index.php?topic=53821.120 .
/Erling
I don't think so as my design is a genuinly phase correct one which from the discussion here seems to be very rare.
Otherwise I was hoping that the irony should come through even in this discussion of matters of life and death, and so I read your answer also. Of course presentation should be as good as possible, and there will be more ways than one to achieve this.
For the moment I am listening to an oversimplified Emerald Physics clone consisting of two Eminence Alphas and a Vifa D27TG35-06 tweaked by cutting its back chamber off mounted in this same MJAO baffle. No waveguide but playing through SRC2496 and DCX2496 EQ this speaker presents itself with an authoritative statement I didn't think possible. So what shouldn't happen with the PE waveguide and proper positioning for time alignment: http://www.audiocircle.com/index.php?topic=53821.120 .
/Erling
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Erling
Whether it is or isn't is not the point. Most of us in this discussion have designs which are "the best in the world" - it's strange how many of those there are!
What we think of our own designs is always too biased to be of much use, so there isn't much point in even expressing such observations. To be reasonable you need the comments of other non-involved parties.
Ah, I see my wording was not clear enough. I meant no *additional* ringing besides that intrinsic and unavoidable effect you mention. If we made a correction filter that would result in perfectly flat phase without correcting the amplitude to flat at the same time this would result in that additional ringing / filter artifacts (at least I found that it sounds grainy/ragged when I tried correction to perfect linear phase while maintaining the amplitude ripple). OTOH if the slopes are not very steep the intrinsic ringing of the indivudual ways would likely not be much of a problem, while with, say, a LR8 response the off-axis summation would be noticably compromised by the ringing, right?
- Klaus