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In Reply to: RE: modify the xo to a more symmetrical alignment at the XO points ... posted by andyr on August 10, 2015 at 13:18:57
I think you guys are still confused on the symmetric versus asymmetric thing. :)
Dave.
Follow Ups:
So why don't you un-confuse us? :-))
Andy
Well, symmetrical is not really necessary but when you have a symmetrical (same fc and slope for both HP and LP) the equidistant placement gives you time alignment.
You can also tweak the XO to get an asymmetric 3rd order LP and 2nd order HP to roughly match up for group delay around the XO so they are compensating for the particular driver to listening point distances you want. Or you can do it the other way round and match the distances to the group delay in the XO filters.
You can also use REW (or DEQX which can also adjust for it) to measure relative delays on the driver outputs
Andy/Satie,The stock crossovers ARE symmetrical. Forget about what the electrical topologies look like.
I've tried to explain this a number of times through the years, but it doesn't seem to be sinking in yet. :)Cheers,
Dave.
Edits: 08/11/15
You are talking about them being acoustically matched to have the combined FR come out flat as the mids roll off acoustically at ~2nd order, but the delays only match up at a particular set of relative distances.
Nope. There's more to it than whether the combined response is flat. Even some asymmetrical crossovers could satisfy that objective. I'm talking about the acoustic roll-off rates of adjacent drivers being complements of each other. That's a 'symmetrical' crossover.As I've mentioned previously also......if your objective is to match relative delays and/or create a constant group delay, then you have the wrong speaker system. It simply can't be done with large speakers like these. I don't care what kind of physical offsetting you do, or relative electrical delays you introduce, or etc, etc.
I'm not sure why you're still misunderstanding basic crossover theory.
Dave.
Edits: 08/12/15
I understand your approach to viewing the speaker as too large to have a successful time alignment. I basically disagree with that. I believe the radiation pattern is much closer to cylindrical and does not have the time smear you expect from the different arrival times from the top and bottom vs the middle. Sound wise, comparing to vandies in my system and Theils elsewhere (quite a few years back) and more recently at a friend's with Revel Studios, Sonus F Cremona, and Focal Nova Utopia, the time smear is simply not there audibly.
When I don't aim the bass panels with the mids and tweeter so that the bass panels can remain face forward with wall loading then you are right and the damn things are plain too big, so just don't allow for time alignment - and the best you can hope for is for them to be roughly in phase, In this case, a steep XO is more beneficial to just get the bass driver output out of the way..
About 6-7 years ago when I tried to measure for time smear with impulses from the REW software I did not get anything significant with the equidistant setup. I also saw some results posted here from DEQX alignment that showed no time smear on impulse tests..
As to understanding the theory, I don't know that I do. Particularly as I never tried to learn the precise nomenclature so will risk often assigning a different meaning to a term than its established meaning.
What I look at is not necessarily a perfect complement in FR as I don't find smallish humps or dips of up to 2 db to be really audible unless they are really broad, and usually peak to trough FR irregularities rarely get bothersome below 4db even if they are audible.. I do find even small time misalignments to be a problem at the mids and treble.as they appear to alter image precision and soundstage size and shape regardless of the (very minor) changes in FR. I know you don't consider these things important, but I do. I am also aware of your thinking that these things are impossible for these speakers.. I don't expect to be able to convince you otherwise and won't put in the energy to provide the measured empirical proof.necessary to convince an engineer. It only needs to satisfy me and whatever caricature of the physics may sit in my mind, I would happily share it in all its fuzziness..
My target FR is definitely not flat but rather slanted to be bass heavy and tilted down somewhat at the high end - that ever since I heard the Nova Utopia at the dealers some 4 years ago and was agape at how well the obvious deliberately shaped FR worked on so many acoustic classical recordings. Electronics were all Boulder source was computer and Boulder DAC. It was a shock to me that this kind of FR was "legit" and worked so well in practice.
If you don't understand the difference between asymmetrical and symmetrical crossovers, that's fine. But let's not be attaching those labels willy-nilly and confusing folks with your incorrect analysis.
I think you're greatly over-simplifying the supposed "cylindrical" (it's really not you know) polar pattern of these speakers in order to fit your hypothesis regarding relative timing differences and their relative importance to the "soundstage" creation. I have no problem with subjective analysis and listening experiences based on different speaker locations, angling, etc, etc. I do have a problem when a person makes incorrect technical conclusions based on that experimentation.
Keep it subjective and you will hear no complaints from me. But when you start spouting nonsense regarding the defined engineering of these systems I might say something. The Maggie speakers have numerous issues (just like all speakers.) But lets not inflate (or deflate) some of those aspects to fit some technical narrative that your subjective evaluation finds convenient.
Cheers,
Dave.
I welcome your criticism and comments as they often correct my (mis)understanding or incorrect use of terms. It allows me to offer my view of how things might be working, as it comes from my own limited experimentation and technical knowledge. It makes sure that readers don't take my speculations as confirmed fact.
However, I do try to help folks with my experiences and my reasoning, however flawed, as to what the physical cause is. I know you would prefer that I just say "I feel" this or that, and note how much mind altering compounds were consumed during the observation period. But I don't imbibe and don't let the subjective observation "just be" but rather try to figure out what I did and why it "worked" or didn't, and use this to plan the next thing to try. I do not take my subjective observation as an isolated internal event unrelated to any physics. I don't accept that Platonic dichotomy.
Who said anything about imbibing or mind-altering compounds?? Not me. That's a ridiculous red herring.How difficult is it to couch all your comments under the umbrella of subjective evaluation and leave the objective technical conclusions to the side??
You create so much confusion on this forum for those that are not well versed in the technicalities of these designs. I've always tried to help the users who are the lowest common denominator (I apologize, I can't think of a better term) with their Magnepan understanding, but you come along and do just the opposite and (many times) post outright incorrect information.
Subjective evaluation has no basis for further discussion. But objective evaluation does.....and that's where the learning can come.
I'm also becoming tired of the off-handed remarks at my engineering acumen preventing subjective evaluation. The two are not mutually exclusive and I have employed both extensively through the years. It's just nonsense to assume that a person can be one and not the other.
My goodness.
Dave.
Edits: 08/12/15
I didn't mean to imply that you are not subjectively sensitive. Nor am I implying - nor intending to - that you being an engineer is an impediment to listening. What would I say of myself then?
If that is the impression you got, I am sorry for creating it. I sincerely apologize.
The issue is that I take subjective observation as telling you something about the physics going on and try to speculate about what it is. When I am wrong I very much want people who know better to say so.
Perhaps I should put a caption on comments that are utterly speculative, or contradictory to established understanding (when I know it). Or just unsubstantiated with measurements. Perhaps I should be running impulse phase and FR tests on REW every time I alter something. I am happier to listen critically when time allows but I don't enjoy setting up and taking measurements that much.
I could be a much better poster and study up on the technical aspects so that I can curb my own speculation when I am on the wrong track, and perhaps go work in a lab where I can have enough measurement equipment to quantify what I am speculating about. But it is not my profession and I am not working with these tools.
I disagree that "Subjective evaluation has no basis for further discussion". Statements like "it sounds better" are only useful if you know how the person's preferences align relative to yours. Observations of sonic qualities using your hearing are not necessarily precise and usually don't provide a quantity to graph but they are not meaningless in ferreting out the physics. They don't just amount to a personal preference. In they're being repeatedly observed by other people when they try the same thing I think they are instructive.
The imbibing comment is an exaggeration of your attitude about subjective evaluation (which I am presuming would include observations). It is the implication that nobody else would hear what I heard. Otherwise subjective observations would be something open to discussion. I am with Harry Pearson on observing with your ears and making the effort to distinguish between realistic natural reproduction and its precision, and euphonic or ugly aspects of it. If a synesthetic like HP could expect others to hear what he did, so should you and I.It is not a red herring, I am making a point about philosophical differences.
I would agree that what makes for a realistic portrayal of voice and instruments varies from person to person to some extent. I would entirely accept that many of us don't want a precise rendition of the recording, or even of the goings on in the recording venue were it perfectly captured on the masters, perhaps some want "better" by "enhancing" some aspects of the playback.
What I'm saying regarding subjective evaluation is that if you tell me you hear something from a particular set of components, it's impossible for me to argue with you about it. And vice-versa is also true.
Collective (similar) subjective evaluations from multiple users might yield a consensus....of sorts....but it's still beyond firsthand experience from another user who might venture a listen.
OTOH, if multiple users have a consensus about the subjective aspects of a particular component, then most likely there is an objective aspect that can be measured to identify the characteristic. I would never assume that's not the case.....as many audiophiles seem to knee-jerk to.
Any interested listener could easily determine the Magnepan 3.6 speakers have extended bass capabilities relative to the 1.6 speakers with a subjective evaluation. But it's a measurable difference.
Subjective evaluation is, by definition, speculation, and can not be made objective with opinion. Would you agree on that? :)
Dave.
No, I don't agree.that subjective observations are defined in that way. If that were the case none of us would have ever garnered any help from the review rags. I, for one, do find that quite a few reviewers can describe the sound of a piece of equipment well enough for me to recognize what they describe when I hear it myself. I even learned to discount the effects of particular pieces in their reference systems which would alter the perception of the reviewed equipment.
Having a perspective (what subjective evaluation actually means) does not negate the reality of the observations, their repeatability, or that something physical rather than a placebo effect is in play.
While people's preferences vary wildly, and really few people have been practicing critical listening and taking notes of what they hear as they vary equipment and parts, enough of us have and can communicate these well enough. Some of us can separate our particular preferences from the observations and describe audio characteristics so that others can get assistance from that in choosing to try one piece over another that may improve a lacking aspect in their system's performance.
I like Art Dudley in Stereophile because he honestly gives his bias and preferences up front, and tells his readers what he is looking for.
Of course, most of us can only describe our reactions rather than the particulars of what hear. Some reviewers just wax poetically so we know well what they feel but have no clue as to what they heard. If you are saying that emotional gestalt descriptions are entirely subjective and provides nothing for further discussion then I agree entirely.
"If you are saying that emotional gestalt descriptions are entirely subjective and provides nothing for further discussion then I agree entirely."
Absolutely. We agree on something!
Your subjective evaluation is meaningless....for anybody else. And their subjective evaluation meaningless for you.
If I evaluate amplifier X and it sounds "warm" to me and you evaluate the same amplifier and it sounds "cold" to you, where does that leave us? Nowhere.
(This is assuming all other equipment is the same.)
This is why I don't pay any attention to your (or anybody else's) subjective evaluations on forums or in magazines or anywhere else. The only subjective evaluation I'm interested in is mine. :)
If you're letting Art Dudley, or me, or anybody else influence your (subjective) thinking on a specific piece of equipment, you have a problem. :)
However, objective testing gives us a baseline....a reference point....that we can compare equipment to/with. Maybe the test equipment is slightly different on my test bench vice yours, or in your anechoic chamber vice mine, but we can understand those differences and characterize them into the evaluation. Certainly it can fall short of identifying all audible aspects of a piece of equipment or speakers, but at least it gives us something tangible to hang our hats on to start with.
I couldn't even convince you on the validity of a simple Thevenin equivalent voltage source issue a while back, so I'm 100% sure I won't ever change your mind on the subjective evaluation topic. But my intention is to try and re-open your mind on objective evaluation and quit the darn speculative conclusions. I'm 90% sure I won't be successful at that either, but I might keep trying.
Cheers,
Dave.
I am not being "influenced" in making an observation, I am informed as to what item to try out according to the description of its sound. Including "warm" or "cold" - though I do like more specific descriptions than that as to subjective FR. All that considering the system it was playing in and more importantly, in comparison to other pieces of the same type in the same system. The comparisons are the most useful info coming out of a review.
I have found some reviewers to be very good on descriptions of what they hear and others to be uneven while some are nearly unintelligible. In some publications there is a tradition of emotional descriptions that I find useless. Particularly since this is often dedicated to extremely expensive equipment.
The point is that when comparing to a reference most folks will hear the same kinds of differences but react differently according to their preferences. So long as you don't ask them what was :"better" or "preferred" etc. you can get some useful characterization.
I have no problem with measurements and find them informative and very useful in making decisions as to what might work in a particular context. But equipment that measures similarly can sound very different. Your standard SS class A/AB 100 watter comes in a surprisingly wide variety of tonal flavors, imaging ability (placement soundstage width image size depth rendition instrument highlighting) detail retrieval, dynamic capacity, Bass tightness and extension.
I think you are missing out on lots of information available on forums and the review sites and rags. You just need to figure out how to read them and who does a better job in pointing out things you perceive and care about.You might even luck our and find someone with very similar preferences to your own.
The problem with measurements is that things like THD are not psychoacoustically weighted. Nobody has a test for how small signals and transients are handled on top of large ones (particularly when loud bass is playing along with not particularly loud high freq and mid content with lots of small transients). There is no test for soundstage and imaging characteristics at all. So while the tests are useful in that I don't end up having a tube SET amp on a reactive speaker or a 50 watter on a 82 db sensitive speaker. Beyond that the measurements have limited use.
Re THD - if hardly anyone can discern <1% 2nd harmonic distortion but is irritated to no end by less than 0.1% 5th and 7th order HD then what is the point of a THD measurement below 1%? Or a measurement of THD above 0.1% when all of it is odd order.
However flawed, subjective characterization is all we have to communicate info on how products sound. You can discount what someone says about detail retrieval if you see their reference speaker is known to you as very poor in that aspect of performance. You can say that you would rather have someone with electrostats or ribbon speakers comment about sources and preamps but you would take his comments on deep bass performance with quite a bit of salt.
I don't accept your view of subjective evaluation at all. That does not mean I reject measurements.
I just read this thread with great interest - especially the discussion of polar patterns and "time-smear" being associated with large line-source drivers (and arrays, I guess).
Does anyone know of any psychoacoustic research that sheds light on the impact of large drivers vs. point-sources? Thinking about the physics of sound propogation from large drivers, they seem problematic, yet in practice (for me) they seem to work fine.
Isn't there a psychoacoustic "summing" effect that applies to reflections or echoes arriving within a couple milliseconds or so of the initial wave-front?
Exactly correct.
These types of large speakers have considerable comb-filtering effects relative to conventional or point-source transducers. Yet, our ear/brain integrates (sums) these extremely well and they don't manifest into a significant problem for domestic listening.
If you were to measure these systems in a free-field environment and move the microphone up/down in the vertical direction you would see a multi-lobed polar pattern with large cancellation nulls at various frequencies. Not pretty compared to more conventional systems.
Cheers,
Dave.
Here are measurements of the Flatline Design (closed after the death of the founder) ribbon hybrid speaker.
The speaker sports a 69" 5/8" ribbon with only two elastomer wedge brackets for damping.
Note the very good impulse response from the ribbon.
No sign of differing arrival times.
The FR plots on the vertical dispersion showed no difference.
The expectation of a departure from a cylindrical radiation pattern in the nearfield is not applicable to continuous line sources but only to spaced line arrays of spherical sources having a substantial vertical component to their radiation. As shown here http://www.jblpro.com/ProductAttachments/AES_Ureda_Analysis_of_Line_Arrays.pdf
Yeah, a very old test. I remember reading that issue many years ago. John's frustration with measuring these types of speakers was evident then and still is now. He's not the only one. I applaud him for making the efforts. It's very challenging to test speakers of this type and get meaningful results that won't be misinterpreted by ignorant audio forum members. :)
"All things considered, the Flatline 175 illustrates why I hate measuring ribbons or other planar speakers: the interaction between the speaker and the measuring microphone is too complex for comfort at practical measuring distances;............."
Anyways, I don't care what you interpret (or misinterpret) from those test results. The distance from a measuring microphone to the center of the line is different than to the end of the line. A comb-filtered objective result will be generated. It's the nature of the beast....if monitored at a design-axis reference point.
I'm not sure if you're attempting to argue basic physics here. I mean, it is what it is....this is not my opinion.
The subjective result is obviously a different story and I will stipulate that speaker system probably sounds fine in a domestic environment with music material. (Even though there were numerous issues with the implementation.)
Did you read section 3.5 of the Ureda paper?
I actually think the Lipshitz/Vanderkooy paper from 1986 is much better written and clearer in illustration, but YMMV.
I'm not making this stuff up. Large speakers are large speakers...they will measure like large speakers. No other result is possible.
Dave.
But I don't see the measurements that show that for a continuous planar line source.
If there were a vertical pressure gradient for a tall line source - essentially floor to cieling- to create significant output from the bottom OR top to reach the listener then it should have showed up in both these measurements of impulse and testing for changes in FR at different vertical angles. Or it should have shown up in those done by our DEQX'ers or by my REW measurements in the prior decade.
I have been hacking google trying to find the measurements that you must have seen to be so certain of this. I see many for cone arrays, dome arrays and tons for commercial sound horns that show how the cylindrical waveform falls apart above a certain frequency. You can also show it in simulations.
However, all I find for long planars is that there is barely any vertical component to the output and very near none for push pull planars/ribbons. Alcons and SLS (and BG too) claim that provides their spiral arrays completely uniform coverage without mid and high freq hot spots or dead spots.from comb filtering. Others in the industry are scrambling to come up with horn waveguides and curved reflectors to provide as close to a purely horizontal launch as possible out of their waveguides to compete with the planar line source makers. Same goal as Beveridge .
I just don't get how the physics of the wavelaunch can allow a pressure gradient to form in the vertical direction off of a long planar in the near field. And therefore how there could be a spherical radiation that would arrive at the listening height from the bottom or top. of the ribbon. All you hear is the output from the center of the ribbon and the rest of it is only there to prevent the radiation from having a vertical component and to extend low end response.
Did you look at Figure 2 (and the others for straight line sources) in the Ureda paper?
It's well described in Section 3 of his paper.The math does get a little involved, but the simplified function is noted in 3.3.
Implementation of the crossover is key in real-world systems, and much depends upon the frequency range the line source is driven. I suspect that's what you're noting with your "no vertical component" observation.
I hope you're not arguing that line-sources have no inherent disadvantages relative to "conventional" and/or point-source radiators. All of them have inherent advantages and disadvantages. If you add up all the pluses and minuses, a point-source radiation characteristic would be optimum in a free-field environment. But those are (essentially) impossible to construct. (At least for a full range speaker system.)
The objective in any speaker system should be to make them as small (acoustically) as possible. Any time you make them larger, things get more complicated. :)
Dave.
Edits: 08/15/15
I see that the first significant simplification in the Ureda calculation is that the distance on axis at th middle of the line is much higher than the height of the array.ao that you are an order of magnitude farther out than you would be in a home setup. The second issue is that listening is largely close to the midpoint normal to the line so the angle (alpha) is 0 or very near it.At home you have a 1.5 to 2 m source and a 2-4 m listening distance. For a full length line source at ~2m height you are at 1 to 2 times L. The ends condition is that the top and bottom are constrained by the floor and ceiling. So the floor and ceiling act as a waveguide to keep the vertical pressure drop and dispersion from developing. I don't know how much of the model holds up for a home setting of a near floor to ceiling line source at 1.5L listening distance at the midline.
This is not to say that there is absolutely nothing coming to your ears from the bottom or top of the line source. And from anywhere else on the line, but the overwhelming amount coming from ear level and the precedence rule would make transients fully unsmeared. The comb filtering effects result in a very closely spaced set of sharp squiggles on an unsmoothed FR scan. But that is less important to our hearing since our FFT breakdown of pitch and harmonics takes much longer (10-30 ms once the steady state pitch arrives) than our response to transient acoustic events (0.001/0.01-1 ms,), which is independent of pitch and harmonic content (and distortion thereof). Our pitch resolution is fairly crude like our amplitude resolution, hence the violinist's practice of vibrato changing pitch in a +/- 5% band is still perceived as a single pitch tone.
Efit: actually our pitch resolution is much much netter than our amplitude resolution at any frequency. But it takes some time and tends to average.
I will claim that in a home setting a line source is going to have an inherent advantage over point sources since the latter do not contribute their own floor bounce cues to those on the recording. That would not be an issue in an anechoic floor and ceiling room. But I don't know how you walk on an anechoic floor made of absorbers,, snow shoes?. Also at close listening distances you can get much less floor bounce (and room reflections) in the mix reaching your ears..
Edits: 08/16/15
Go look at Alcons (Germany and USA) and SLS audio as well as Meyersound who make commercial line array PA systems The first two use planar sources for the upper band which have terrifically clean waterfall plots, They measured that the planars have a 94% horizontal radiation along their length with an insignificant vertical component, and Meyersound pateneted the "Ribbon Emulation Manifold" or REM waveguide that produces a nearly all horizontal radiation pattern.
All of them challenge you to stand under their line arrays and detect any direct radiation from them.
They don't post much in the way of measurements but they have colorful pictures of the acoustic simulation software showing that the radiation is very cylindrical.
Meyersound went to the trouble of showing why discrete horn drivers in standard horns do not produce a uniform cylindrical wave.but continuous sources like ribbon drivers do. Hence the high speech ineligibility they achieve and lack of hot spots and dead spots in the radiation coverage zone
While the bass panels should be considered point sources over most of the range below 200 or so hz, the other drivers are defacto continuous line sources that produce a real cylindrical wave with hardly any vertical component. So there is no time smear.
http://www.alconsaudio.com/pro-ribbon-2/
http://www.slsloudspeakers.com/SLS%20Audio%20LASS%20Line%20Array%20Simulator%20Software.htm
http://meyersound.com/support/papers/line_array_theory.htm
As I have the mid & ribbon drivers in separate frames from the bass drivers, I can move the mid/ribbon frames forward of the bass driver frames, to time-align them.
Later in the year (when I add subs) I expect to move to dsp - so will have more flexibility in terms of dealing with filter delays.
Andy
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