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Bifwynne,
welcome.
I figured that these links would NOT be wasted on you. :-)
indeed, speaker design is a complicated affair. Fully understanding what's going on takes skill, knowledge & experience as speaker design involves the mechanical aspect of actually building the speaker but also understanding what the electrical effect of the x-over is to the mechanical aspect. It's an inter-disciplinary expertise.
In those links, there's a lot of chatter by members who don't know what they are talking about & by those who are airing their thoughts & experiences. You can skip over that which will shorten the reading time. Pay closer attention to the speaker manuf posts. Those are revealing in info.
Well, now that you have the amp-speaker interface licked :-) it's time to go a bit downstream & understand what that electrical-to-sound transducer is all about... |
06-21-14: Bifwynne
Bombaywalla, I have a follow up question. How are small speaker manufacturers able to design speakers without the benefit of the R&D budget, engineers, and testing facilities that some of the larger manufacturers have at their disposal. Bifwynne, as Timlub wrote earlier, I don't think it's necessary to have an extensive R&D budget, scores of engineers, anechoic chambers & mutli-million $ machines to make a good sounding speaker *iffffff* the manuf really knows how to design a speaker. The companies that you stated need this to make-up for their lack of knowledge of speaker design. Focal has gotten better over the years. when I 1st heard their Electra series speakers, they sounded like sh**. Their ultra-expensive speakers have a big wow factor but nothing more. Those R&D budget, scores of engineers, anechoic chambers & mutli-million $ machines are good marketing hype items that sells. ;-) of course, my opinion based on listening to many of the cited manuf's speakers. If one really knows what one is doing then it is possible to select & buy speaker drivers made by OEM speaker driver manuf that are superlative in their specs & performance. The next thing to do is to design a speaker integrating those drivers into a cabinet such that sum of the two is greater than each part. Al and Ralph .... where are you??? :)
Bifwynne You know Bifwynne, it is entirely possible that Al & Ralph cannot help us here. Raplh is an amplifier expert & the fine points of speaker design might not be in his 'quiver of arrows'. Same for Al. Unlike explaining electronics, one cannot explain way speaker design unless one has dealt with this complex task. Yeah, everything is a compromise - engineering is an applied science. By its definition it is supposed to make compromises to bring about a solution. The key is: which engineer makes the best compromise? I believe that the 3rd link I stated clarified your earlier question re. the difference between time coherent & phase coherent. The sloped baffle gives you a time alignment of drivers but does not tell anything about the time or phase coherence of the speaker. Another thing I learnt was that just because a speaker has a 1st-order x-over does not mean that the speaker is time or phase coherent. I found that a lot of speaker manuf hide behind their using a 1st order x-over. I found that many such speakers used a 1st order x-over but their drivers were some higher order (such a 2nd or 3rd) which means that the driver performance rolled off with a higher order well before the 1st-order x-over kicked in. So, in effect, such a speaker is a 2nd-order or 3rd-order speaker & not a 1st-order speaker. To be truly a 1st-order speaker the speaker has to be electrically & mechanically a 1st order speaker meaning to say that the driver's performance needs to extend beyond the x-over point so that the roll-off is being done only by the electrical x-over network. it's complex material that cannot be absorbed in 1 reading. I've those threads printed off & re-read them from time to time to refresh my understanding. Each time I extract new info from them. Like Unsound wrote earlier the 1st thread & I think the other 2 as well are some of the very best threads to have appeared on A'gon. |
Bifwynne, Ok ... if Tim or Bombaywalla catch this, here the ultimate Q. How can one tell whether a speaker is time and phase coherent? Critical listening is one of the methods - when a speaker is time-coherent then it will get the timing right for ALL genres of music. Recordings otherwise painful to listen to will be less painful (because the speaker is not distorting the music signal coming to it). In time-coherent speakers you forget the audiophile attributes (pin-point imaging, soundstage width/depth/height, etc, etc) & you focus on enjoying the music. The other method, as stated by Unsound & 2nded by Al, is the time-domain step response. Usually Stereophile (as indicated by Al already) & Soundatage reviews http://www.soundstage.com/index.php?option=com_content&view=article&id=16&Itemid=140 do a pretty good job of showing all the measurements they have done on various loudspeakers they have resp. reviewed. Thanks Tls49 - you have pointed Bifwynne to a really good website for reading on time & phase coherence. I always look to Roy Johnson when I have questions on this subject. To me he is skilled in this field & has dedicated his life to making time-coherent speakers since he began his biz in the 1980s. Green Mtn Audio speakers are the only speakers that I know of that are time-coherent across the entire audio band from my personal experience. I know that several people believe that Vandersteens & Thiel speakers are also time-coherent - I personally do not have any experience w/ either of those brands so I will not comment. First, the Vandy 7's step response plot shoots up like a rocket and then quickly rolls off and stays down. By contrast, the Studio 2 shoots up, rolls off and then rolls back up again. What does this mean? Why the differences? Why the differences? Because the Vandy 7 is time-coherent & the Revel2 is not! Bifwynne, if you click on the link provided by Tls49, you will see exactly why as you read the text there. Scroll down where Roy J talks about time-domain response & he shows how a step response looks when the speaker is time-coherent & when it is not. The Revel2 are clearly not time-coherent. I'll ask again, how important is time and phase coherence? To me it is everything! I used to own B&W speakers & I have heard speakers from many, many different brands now both auditioning at dealer locations & at multiple RMAF shows, at various friends' homes, etc. The sonics from a time-coherent speaker are in a totally different league. For me time-coherent speakers "get it" while all others simply do not. Once I heard Roy Johnson's Green Mtn Audio speakers & owned one for many years, I realized what the heck time-coherence was all about. Now, I cannot listen to any speaker if it's not time-coherent - very quickly I will realize the lack of time-coherence & I will immediately perceive that the music has no life & no PRaT & to me it will just good/superior sonics but not music. I want music from my speaker & not good/superior sound - I didn't pay top $ for good/superior sound; I paid top $ for music thru the speaker. These days I stick to time-coherent speakers - my selections are very few but it's worth every penny to me. This should be the case for everyone if you are interested in listening to music. Many of friends are into superior sound (& not music) so they are on a perpetual merry-go-round for speakers - speakers come & go thru their music rooms. They are always wow'd by a new speaker & later after a few months or a year, that speaker is sold & another one takes its place & the cycle repeats. In my mind I'm thinking that I've made my case for time-coherent speakers - you buy it once & then you sit back & listen to music because a time-coherent speaker will play every genre without tripping up because its physics is right. Of course, IMHO. YMMV. |
Bombaywalla, did you or Tim mention that one mark of a phase coherent speaker is one which has a flat impedance and phase plot. Take a look at the Magico S5's specs. Is there anything else apparent from the NRC tests that permit inferences about phase coherence? Bifwynne, don't know whether I or Timlub wrote this - I don't recall writing this in this thread. Maybe in some other thread you & I contributed to? Anyway, looking at the Magico S5 measurements, even tho' the imp & ph plots are less bumpy than many others in the market, there is still quite a bit of phase shift. Plus, at 2KHz the speaker goes from positive phase angle (inductive) to negative phase angle (capacitative). This can be quite burdensome for the amp - the phase relationship between the current & voltage changes very suddenly & the amp has to react to that instantaneously. This is difficult to do. Looking at these impedance & phase plots I cannot confirm whether or not this speaker model is time-coherent. Probably not as I've not seen Magico design any speaker thus far that has been time-coherent. Maybe the S5 is a departure from that norm - don't know - but if I'd have to guess, I'd say 'no'. OTOH, for, say, Green Mtn Audio speaker I'm used to reading specs that look like this. For the C3 speaker model, for example: Response +/- 0.75dB from 40Hz to 21kHz, -3dB at 35Hz and
23kHz, from 2.5 to 6m, on Soundfield Converged axis, on first arrival
tone bursts, across approx. 80dB dynamic window.
Phase shift +/- 3 degrees acoustically, from 160Hz to 8kHz.
Does not vary with loudness.
Impedance 6.5 Ohms, +/- 0.75 Ohms 150Hz to 20kHz. Does
not vary with loudness. My brother owns the Callisto bookshelf models & their specs are: Response Freefield at 2m: +/- 0.75dB from 55Hz
to 20kHz, -3dB at 47Hz and 21kHz. Typically -3dB
at 47Hz on 24 speaker stands at 8 distant.
Phase shift +/- 2 degrees acoustically, from 200Hz to 8kHz
on listening axis. Does not vary with loudness.
Impedance 4.8 Ohms, +/- 0.75 Ohms 100Hz to
20kHz. Does not vary with loudness. In both the Green Mtn Audio speaker specs, now, we are talking flat impedance & phase response. :-) Nothing like that in the Magico S5. (Once again, I've experience with Green Mtn Audio speakers hence I bring them up time & again. If other members have similar specs for other time-coherent or phase-coherent speakers, please share those specs. Thanks.) |
Hi Roy,
good to see that you discovered this thread. :-)
Duke, you are always gracious.... :-)
hope that Bifwynne takes advantage of your resp. presence here & gets some deep technical dialogue going..... :-) |
it is true that the measurements by reviewers are few for Green Mtn Audio speakers. I don't know why?
I believe that Green Mtn Audio speakers are different from conventional high-order x-over speakers that are prevalent in the market. If one is used to measuring the conventional high-order x-over speakers that are prevalent in the market that same technique is unlikely to work for Green Mtn Audio speakers because of the requirements of the distance & listening axis required to ensure that the drivers integrate. I believe that JA was not knowledgeable about this when he did the meausurements for the Diamante speakers. I also understand from the manuf that JA was advised by the manuf many times how to setup the speaker to measure it correctly but JA completely ignored the manuf's recommendations & did his own thing. The result is poor measurements & also measurements done incorrectly.
Yes, the slopes of 1st order x-over are shallow compared to 2nd or 3rd or 4th order x-over so signal will bleed thru at high levels. While 4th order x-over speakers can be driven to 120dB SPL, 1st order x-over speakers can be driven to something like 105dB SPL. If this is a no-deal for you, so be it. But 105dB SPL for in-room/in-house listening is plenty loud by any stretch of the imagination. Yes, it's not outdoor rock concert SPL.
Have you owned any Green Mtn Audio speakers by which you claim " All and all, a concept that does not really work, due to all the other problems it create."?? Or, are you one of those people who reads reviews & makes decisions based on the printed word? Or, are you a speaker manuf with an axe to grind?
Because I speak from personal experience & from the experience of my friends & relatives who own & have owned Green Mtn Audio speakers. Everyone that I know of has had & is having an excellent experience with these speakers. Yeah they have limitations (which speaker does not?) but their limitations are of ommission rather than of commission.
I do not intend to convert you to 1st-order speakers - never intended to for the get-go - please buy what you like & enjoy it. But I would not make such sweeping remarks without personal experiences.
Anyway, this thread is about "sloped baffle speakers", "time & phase coherence". There are very few speakers that meet the time & phase coherence criteria & I believe that Green Mtn Audio is one such brand hence it gets brought up time & again in such discussions as an available commercial product. I'd prefer that this thread not take a downward spiral focusing on Green Mtn Audio speakers or Green Mtn Audio bashing. Let's keep the discussion on "sloped baffle speakers", "time & phase coherence". Thanks. |
06-24-14: Kiddman
I would have to see the detailed measurements to accept the, I agree with this as well. It's just too bad that there aren't many to view/study.
IMO, unlikely results claimed by this manufacturer.
I disagree with this statement (given my personal experience) but I would have written "unverified claims by this manuf". Owning & listening to those speakers leads me to believe that such type of specs are achieveable by this manuf. Investing hours in driving to dealers, or flying, asking manufacturers to let you hear them, flying to audio shows, those are all much better ways to make an educated guess about how you will react to the sound in your home. indeed, I have done most of the items in this list - I have not asked manuf to loan me speakers to listen in my home - but I've done all the other items. I was at RMAF2013 & listened to 95% of the rooms in the Marriott Tech & walked over & listened to all the rooms in the Hyatt. I heard a lot of speakers - most speakers were in "bad" rooms (typical show environment) except for those speakers put into huge ballrooms & other conf rooms. Most of the speakers sounded very blah except a very few. And, one of them was the Green Mtn Audio room. I was there all 3 days & I listened to the Green Mtn Audio Eos speakers each day. After hearing so many blah sounding speakers, it was a relief to listen to the Green Mtn Audio Eos - they sounded like music, great dynamics & Roy was playing all kinds of music (not audiophile CDs - just regular redbook music). Those speakers sounded good on every genre. This excellent sonics caught the attention of Stereophile: http://www.stereophile.com/content/marigo-whirls-green-mountainFWIW. IMHO. YMMV. |
And here's my personal bottom line. Phase coherence is just one of many variables that is taken into account when designing a speaker system ... and there are many. As many folks have said, trust your ears and audition as many speakers as you can. But ... if I was asked to buy speakers based on their phase coherence characteristics as a stand-alone factor, I personally would not. Bifwynne, I disagree here. Of course, you are entitled to think about this the way you choose, just as I am. There's too much research - of the wrong type - that convinces people that time-coherence is one of the many issues/parameters to be resolved in speaker design. After hearing time-coherent speakers vs. others, the speaker should be designed around time-coherence & issues re. that speaker's design should be solved in the context of time-coherence. When that speaker is correctly built as a time-coherent speaker it will simply be far more realistic, dynamic & accurate to the recorded music than any other speaker in its price range. From my experience, I'm convinced - there ain't no other way to go..... Others who have also had such an experience feel the same way not surprisingly. sorry to see that (once again) this crowd has missed the point re. time-coherence. :( When you have a chance, listen to a time-coherent speaker (doesn't have to be Green Mtn Audio) & compare it a non-coherent speaker..... |
I believe one of the members had posted that the tweeter is 180 degrees out-of-phase in a 2nd order system. I believe that this is wrong info. If you read Roy Johnson's 1997 article in Audio Ideas Guide he says otherwise & I quote Contrary to popular belief, the 180-degree shift doesn't mean that the tweeter is out of phase with the woofer. It merely leads the woofer output by 180-degrees, or half of the wavelength of the crossover frequency....
Figure 5b also shows that the amplitude response (derived from steady-state tones) will have an infinite 'suck-out' Tw + W. At first glance, this cancellation does, indeed, seem exactly like that caused by a tweeter with reversed polarity. What is really true is that the time delay is causing cancellation on steady tones, because the time delay at the crossover frequency is half of a wave cycle, 1/(2f) seconds.
To 'fix' the problems of the system, a designer will often reverse the tweeter's wires to invert its polarity. Although the steady-state results shown in Figure 6a look much smoother, in reality this is because the graph for the tweeter's phase has had 180 degrees subtracted.
This seemingly minor point forms the basis for the many claims of 'phase-coherent' performance, which, at best, is a half-truth. The graph now shows 'a smooth rate of phase-angle change at the crossover point.' But it isn't smooth from the perspective of time passing by. In fact, regardless of how smooth this curve appears, the woofer and tweeter still have the same sequence of arrival as before.
Reversing the tweeter polarity only means that the tweeter is moving inward on the initial pulse while the woofer moves outward. This is evident in the square wave response in Figure 6b: The tweeter is pulling in while the woofer is pushing out. At the highest frequencies, the tweeter still arrives as before (in Figure 5), and now its absolute polarity will still be backwards.
I think that Al already provided us a link to this 1997 article so I will not repeat it here. I want to flip the switch and listen to music. Not interested in using an oscilliscope to figure out how to enjoy music. precisely! Even more reason to own a time-coherent speaker. Time-coherent speakers, when compared to non-time-coherent speakers, when properly designed, will be more dynamic, more true to the recorded music & simply more realistic. That's the kind of speaker to have in one's room if you want to simply "flip the switch and listen to music". With time-coherent speakers you will leave the oscilloscope on the test rack (where it belongs) & you listen to music. Problem is that we don't hear distortion as distortion, not unless you have the trained hearing of a professional under controlled conditions. It can be measured by instruments but human brains interpret those as frequency differences and there could be any number of explanations including comb filtering, diffraction, or the driver. Almost as easily, they can be masked.
So, forget the test, it's useless. I think that this is a bad attitude to have. Basically this says, "you are not trained to listen & you are not getting it, so drop this issue & don't make the effort to learn. keep the status quo". I say that if one wants to become a better audiophile, a better listener, a better consumer, one should challenge oneself to reach higher & try to understand things that are at this time outside one's grasp. One should challenge one's norm or the norm & you might find out that there is indeed a better way to do things & this enlightenment might bring more satisfaction & joy in listening to music. if you surf the Green Mtn Audio website, there are article on how to listen. http://greenmountainaudio.com/how-to-listen-to-music/http://greenmountainaudio.com/how-to-choose-speakers/One needs to understand that if a speaker is not time-coherent, no other parameter will make up for this. When it comes to time-coherence, you cannot juggle it/trade it off w/ other design parameters - you either have time-coherence or you don't. Time coherence is not a 'fascinating' concept or idea. It's real & properly implemented makes the difference between enjoying music & listening to top quality sound..... |
Hi Ngjockey, OK, thanks for the clarification. :-) In GMA's specs, they state phase shift acoustically over given frequencies. Does that mean impedance phase (reactance) or total phase? Either way, impressive. this is really a question for Roy Johnson (who designs these speakers) but from my many detailed chats with him & from my ownership of his speakers, I believe that he is citing total phase shift - it's acoustical & electrical combined. The driver selection is critical to achieve this kind of minimal phase response. If you read that same Audio Ideas Guide article he clearly states that driver selection is key & I quote .....What he means is that the drivers must be well-behaved far beyond their crossover points to be used with a first-order circuit, because this circuit allows the drivers to overlap across a wide range. To be used with a first-order crossover, only the best drivers need apply. The "he" in the above quote is referring to Siegfried Linkwitz, just FYI. Roy J: you might want to chime in to clarify your speaker spec. Thanks. |
Thanks for chiming in Roy. :-) Thanks for the explanation in your long post. |
07-04-14: Kiddman
........I have to submit that time coherence is not the driving factor in speaker sound.
Put another way: an absolutely horrible, highly distorted speaker that is time coherent could easily be made,..... Kiddman, I'm afraid you are quite clueless & remain so. you really have no idea, do you? The more you write, the more ignorance you show in this matter... |
07-05-14: Kiddman
For a ubitiquous speaker that shows good time alignment, look no further than Vandersteen Model 2............
So there you have a great example: a manufacturer that makes a barely passable (to my standards) time coherent speaker........ Kiddman, you are screwing up again!! In your 1st sentence you wrote that the Vandy Model 2 has TIME ALIGNMENT. In a sentence much you lament by saying that the Vandy Model 2 is TIME COHERENT (which is wrong) & how could it be so bad sounding. The Vandy Model 2 is time-aligned & that's it. The Vandy Model 2 (therefore) is NOT time-coherent. Time aligned speakers are NOT necessarily time-coherent. The other way is true - time-coherent speakers are time-aligned. Ever since you participated in this thread, you have been NOTHING but negative - casting doubt on this subject matter & being insulting - and, yet, you have contributed NOTHING & no information to this thread/subject matter. By reading your posts, other Audiogon members gain no new information except determine that you are a stubborn 'nay-sayer' with perhaps little experience. If you have no positive contribution to make, go find another place to spend your time rather than driving off the other members who come here to learn something new & different. Your negativism benefits nobody.... And, don't cast doubt on my experience & education, you jerk! |
Bifwynne, yes, I think you have the list.
Single-driver speakers are also time coherent (since they dont have a x-over to begin with) but they might not have the freq range extension you are looking for.
Some of the latest generation Martin-Logans might also be time-coherent (they claim to have made big strides in integrating their woofer with their ESL panel) & the full-range CLX.
Quad speakers are also time-coherent such as the ESL-2085 & they might other models (ESL-989?)
Another brand is Eminent Technology LFT 8. They might have a latter rev of this model, not sure.
Yet another brand would be Sanders Sound Systems 10C & 11 ESLs. You'll find measurements of the Innersound Kaya & Eros Mk3 speakers on Stereophile if you search. Innersound speakers were basically made by the same person who owns Sanders Sound Systems today. I realize that I'm extrapolating since Innersound Kayas were time-coherent that Sanders Sound Systems 10C/11 will also be. This is based on a reasonable assumption that the same designer has not changed his philosophy when he started his new company. Atleast I did not get this impression when I spoke to him in Dec 2013/Jan 2014.
I'm almost willing to say that SoundLab ESLs are also time-coherent but I might be wrong here. Not sure.
That's all I can think of right now. If I think of more brands/models I shall post. Thanks. |
07-05-14: Kiddman
Yes, I do doubt your experience and you sure sound like a guy with no technical education and little technical aptitude. Anyone who is fixated on one aspect of design and thinks it guarantees something is usually one who has little technical experience or knowledge. Someone who has experience and physics and engineering in his background always knows designs never hinge on one parameter or feature. listen, Kidboy, if you think that I have no technical education or background then you are deeply negative in that area! I had a good laugh when I read the above... the more you write, the more you put your foot into your mouth. At this point you've swallowed your 1st foot & your 2nd foot is well on its way down. Like I wrote before, you are totally clueless on this subject matter. Time-coherence is not a "parameter or feature" of speaker design; it's a speaker design philiosophy. The designer 1st decides if his/her speaker is going to be time-coherent or not. Based on this decision, he/she selects drivers, x-over topology & then determines to solve all the other issues in designing that speaker under the umbrella of time-coherence. You are far from getting that this concept. I suggest that you change your moniker to 'more_than_clueless' (BTW, you are the one who started insulting various Audiogon members & I'm just returning the favour as I wont sit back & take your sh$$. you are a most unsavoury fellow who doesn't know how to debate a topic without insulting people. That's why I wrote - if you are going to uncivil, go find another place to waste your time. Other Audiogon members do have disagreements but we all try our best to remain civil). the Vandersteen 2 are time and phase conherent.
And that surely does not make it a state of the art speaker, like it makes no speaker state of the art. And, look at your depth of knowledge on display here to the rest of the A'gon community! Your writings repeatedly say that just because the Vandersteen 2 model sounds bad that selecting time-cohrerent as a design "parameter" will not make any speaker sound its best. Wow! diffident mentality here. The Vandy 2 is a really old model speaker & it's very possible that Vandersteen was limited by the driver technology available back then. It's only recently that he started drivers made to his spec - maybe he realized the limitations of what was available to him commercially? I know that a lot of the manuf who make very good drivers have stopped selling them to the public. I had a friend who owned a pair of Vandy 2 which I heard for a short period of time & long ago & not enough to make a judgement on their sound. Once again, time-coherence is design philosophy & not a design parameter. have you heard any other time-coherent speaker? Or, are you basing all this on the Vandy 2 speaker? Time coherent speakers are not easy to make esp. with cone drivers that's why you have very few manuf in this arena. Your pee-wee brain has informed you that it's because time-coherent speakers don't sound good so manuf have dropped the idea. Wow! Perhaps it could be these speaker manuf incompetence in understanding time-coherence & translating that to a product that can be sold that has prevented them from manuf a time-coherence speaker?? Nah, that possibly cannot be the case, right?? |
Lewinskih01, it appears that you are going down the path of (Boothroyd-Stuart) Meridian (the UK-based company). If you were able to stuff your amps into your speaker, you'd have an active loudspeaker like Meridian's along with your DSP x-over. OK, so now your are not listening to passive x-over components; you are now listening to the sound of your DSP software which is processing your music signal & creating delays to align the sonics at your ear/destination. when it comes to using a DSP x-over another company called Emerald Physics is also using this concept. I've listening to their CS2 & CS3 speakers quite a bit - both at shows & at a dealer's place. Somehow I never took to their sonics. It also did not help that a new revision of the DSP x-over arrived every week or every couple of weeks with the pledge that it was an improvement over the prev rev. IMO, with DSP x-over you sonics will be heavily influenced by the software (very much akin to having an oversampled/upsampled DAC - here again, the quality of the sonics is heavily dependent on the upsampling/oversampling algorithm. You already know for yourself that there are some oversampling/upsampling DACs you like & others you do not). I personally think that it's much easier to overcome the sonic short-comings of passive x-over components than it is of the DSP software. At any rate this post was to cite the trade-offs (which I'm sure you already know). I applaud your effort, which is a big one - biamping or triamping & getting all delays & phase of the music signal correctly lined up. I sincerely wish you all the best. Do keep us Audiogon members posted on your progress. It seems premium driver (top Raal, Accuton, scanspeak, etc) can be had for relative low prices (compared to speakers that carry them). what is your definition of "premium drivers"? Cost of the driver? Cost of a commercial speaker using this driver? The marketing hype surrounding that driver that makes you believe it must be the best? From the little I know, some Scanspeak drivers are very good performance that would qualify for time-coherence. Accuton drivers need not apply for time-coherence. I don't know much about Raal. Be careful how you choose your drivers - don't let cost be the judge - look at their freq bandwidth & where you intend to cross them over. FWIW. |
Lewinskih01
....What would be premium brands sound-wise?.... Well not sure how many of these brands are still accessible to the public but.....Scanspeak makes some very good drivers, another excellent brand for woofers is Audax & Peerless, yet another brand for mids & tweeters is Morel & Eton. I'm sure that there are many others. BTW, I never thought about drivers not being time-coherent..... I thought time misalignment was between/among drivers. yes, you are right - drivers in & of themselves are not time-coherent. Drivers are linear (wide frequency range of operation) well above the frequency at which you cross them over. Using such drivers greatly helps to manuf time-coherent speakers because the driver itself does not come into play, it's just the electrical x-over (or in your case the electronic x-over since you will be using DSP). yes, you are correct - time misalignment is between/among drivers. But you made me remember about Meridian's approach. I will look into it. I believe they deliver a digital signal to the speaker and then convert it to analog inside the amp. I'll check if they have processors that deliver multiple analog channels, :-) that's the point of these forums. Yes, you are correct - they do deliver a digital signal to their speaker & convert it to analog inside the speaker box. Pretty complicated stuff w.r.t. all the signal processing they do. How long has Meridian in business? I would say some 40 years. How many people own & appreciate Meridian speakers? I personally don't know any. Doesn't mean that there aren't any/many. Also check into Emerald Physics' methodology. Just a thing to be aware that you are putting all your trust into that DSP software & the handles it gives you to vary x-overs & slopes, etc. I hope that you like the exact flexibility that is given to you & that you are not saying "I wish this software had this other XYZ flexibility". The DSP signal processing is touching your music signal in a very fundamental way in that the entire music signal has to go thru the DSP before you can hear it. Same deal with the passive x-over. But the difference is that you change the quality of the cap or the inductor or the hook-up wire & you can change the sound to your liking. It appears that it's not that simple with the DSP software - you cant go in there & change the code. Or, maybe I'm not thinking of this correctly? So, if I'm envisioning this correctly - computer digital out runs into the DSP software which breaks the audio signal into highs, mids, bass. You get 3 digital streams now. You feed these 3 streams into 3 identical DACs or 1 Pro quality DAC able to output 3 analog streams (one box would be better as everything sits in 1 chassis & has a better chance of being matched to the other analog stream). Then 3 analog streams into 3 power amps - you need to match these very well too: same input sensitivity, same gain, same sort of clipping algorithm, same dynamic headroom extension, same power output capability, same current source/sink capability. There are a lot of variables to contend with. That's why I wrote earlier that it's a huge undertaking. You'll have to become very savvy with DSP (which is discrete-time) & analog signal processing (which is continuous-time). There aren't many people who make speakers using this technique - Meridian, Linkwitz DIY, Emerald Physics that I can think of. maybe this is the wave of the future??? |
07-06-14: Bifwynne
......The tweeter uses an ultra low mass.....
......Similarly, the mid driver uses an extremely light and strong cobolt/aluminum cone..... Bifwynne, do you see what's happening here in the Paradigm drivers?? they are being made light-weight, rigid. Which other driver by the very physics of is light-weight? An electro-static panel driver. You make it rigid by putting a stator around it (like Martin Logan & SoundLab). You'll find that the ESL drivers are linear (flat freq response) over a very wide freq range & that really helps make ESL time-coherent speakers. Not all of them but many of them. The cone drivers are all aspiring to become like ESL drivers - light-weight, rigid. The hope is that the drivers are out of the pix when the signal gets crossed-over. @Bombaywalla -- got a Q. Do most drivers remain linear through their selected pass-band with respect to time delay. In other words, when pulse testing a speaker, is it just the X-over that causes the tweeter to respond first, followed by the midrange, and then the woofer? Bifwynne, the x-over is electrical & the drivers are mechanical (the spring & weight analog that was in one of Roy Johnson's papers that Almarg pointed all of us to in a post w-a-y earlier). So, there is some phase delay thru the electrical x-over as the signal gets low-passed, band-passed & high-passed but there are delays thru the drivers themselves as well. The fastest to respond is the tweeter. More delay thru the mid & the most delay thru the woofer driver. Every driver is flat over a certain freq range before it rolls off. How wide that freq range is depends on the driver was made by the manufacturer. is there anyway to compensate for the time delay phase distortion through the pass-bands of the drivers? Or is that analogous to unscrambling an egg. That is the damage is done ... no fixing it with more passives. no, I believe that there is no way to fix this - once the transducer has converted the electrical signal to sound pressure it has already imparted its signature onto the sound pressure wave. The damage is done - I cant grab the air in the room & push it back onto the driver to give it one more go-around nor can I take that air in the room & convert back to an electrical signal & push it back into the amplifier for another go-around. Impossible to do. Your analogy of unscrambling an egg is a good one. Not sure if this hit the point, but I own a self powered Paradigm subwoofer. The sub permits adjustments for loudness and frequency cut-off. But of relevance here, the sub permits phase alignment adjustments and I assure you ... it makes a big difference. Suck-out or no suck-out at the X-over point (35 Hz). Bingo!! So, you have experienced some effects of phase alignment & seen the dramatic effect of it. You've been holding out on us, Bifwynne! LOL!! :-) OK, so you now know just how important phase is to the bass response. Imagine doing this over the entire audio band? You are now trending towards a time-coherent speaker.... You see something like this in speaker time-domain response measurements in Stereophile & SoundStage where the woofer is in phase or out-of-phase with the tweeter. you can see the suck-out in the impedance & phase curves. |
Bifwynne, I would very much like Roy J to jump in here & answer your question..... Meanwhile, have you read Roy's white paper on "Time & Phase Coherence" on his website? http://greenmountainaudio.com/time-and-phase-coherence/when you read this paper, skip the initial part & read this section titled "Time Coherent Speakers". You'll see the response of the individual driver & how they add up in a time coherent speaker. Then scroll past the rest of the material & read the section titled "Where a speaker goes wrong". I *think* you might get many answers (maybe not all) to your questions. Thanks. |
Let's assume we have a single dynamic cone speaker with a pass band of 35Hz to 20K Hz. Let's forget about high frequency beaming and cone breakup. Just assume this hypothetical speaker has a flat frequency response within its pass band, as measure on axis. Bifwynne, I agree with Ngjockey here that if your hypothetical speaker has a flat freq response between 35Hz & 20KHz then all signals in this frequency region will pass thru minimally unaltered. That's the meaning of "pass band" - frequency passes thru minmimally altered. This, of course, means that in the 35Hz-20KHz the effect of the speaker coil moving inside the magnetic field poses no issues. So, there should be almost zero phase shift in the 35Hz-20KHz region. Is there a frequency range where a speaker is phase coherent yes, its phase coherent inside its pass-band. In the case of your hypothetical speaker it's phase coherent within 35Hz - 20KHz. or does phase nonlinearity increase as a function of frequency ... period?? yes, it does. And, in the case of your hypothetical speaker, phase coherency degrades below 35Hz & above 20KHz both of which are outside the pass-band of the speaker/driver. If the answers to all of these questions are -- yes, then it seems to me using 1st order X-overs and sloped baffles is at best a rough justice engineering response to a problem that is inherent with dynamic speakers that use voice coils. Bifwynne, I'm not sure that you realize what the benefit is of using 1st-order x-over? The benefit of 1st-order x-over is that the PHASE DIFFERENCE (not talking about the absolute phase of a certain frequency) among all the signals in the audio band (20Hz-20KHz) is constant. So, you have a music signal coming into the speaker. This music signal is a complex mixture of many frequencies. All these frequencies have some absolute phase that is different from each other. Further, each frequency has some non-zero phase difference with another frequency in this complex music signal. So, this whole complex music signal now goes into a time-coherent speaker as an electrical signal & comes out as a sound pressure wave. The phase difference amongst all the frequencies in this complex music signal do not change (i.e. remain the same) if the speaker used a 1st-order x-over. This means that the timbre & harmonic structure of the music remained unchanged as it passed thru the speaker. No other higher order x-over can achieve this i.e. higher order x-overs change the phase diference among the many frequencies of the music signal as it (music signal) passes thru these higher order x-overs. So, ifffffff, the solution is a moving target (as you wrote) a time-coherent, first-order x-over speaker is the least damaging (IOW, the best compromise solution to a moving target problem). hope that this helps some..... |
07-06-14: Sounds_real_audio
I have a question. If an 18kHz sound left its' source and a 30Hz sound wave left its source at the same time. would they both get to the listener at the same time? No, they would not. If you have the driver creating the 18KHz signal & the other driver creating the 30Hz signal mounted on a perfectly vertical plane, the acoustical center of the 18KHz driver would be in front of the acoustical center of the 30Hz driver. Due to this, the 18KHz signal would get a head-start & would reach your ear 1st. You hear this all the time at shows - the music is always "tipped up". You hear way too much high freq & the bass seems to be missing. The speakers are not time-coherent & often the drivers are not time-aligned. If I remember Roy Johnson's paper, the woofer driver has a 90 degree phase lag in its pass band meaning that it starts to produce the 30Hz signal 1/4 wavelength of the x-over frequency later than the tweeter driver. That's why you see sloped baffles with the tweeter on top - the furtherest away from the listener's ear. This aligns the acoustical centers of the tweeter, mid & woofer drivers to give them a chance to arrive at your ear at the same time. hope this helps..... |
Hi Timlub, Ok, no problem. I believe his real question is "do all frequencies move at the same speed" yes, all freq travel at the same speed. But the answer to his question is still "No, they do not arrive at the listener's ear at the same time". I tried to explain that in my post - looks like you missed it? I'll cut & paste here again for your convenience: " the acoustical center of the 18KHz driver would be in front of the acoustical center of the 30Hz driver. Due to this, the 18KHz signal would get a head-start & would reach your ear 1st." if you do nothing to compensate for the fact that the acoustical centers of the 2 drivers are different, the highs arrive earlier. hope that this clarifies. |
07-07-14: Bifwynne
.....I still wonder out loud whether speaker inductance as a function of frequency response in fact remains constant within the speaker's pass band. Indeed ... even if speaker inductance remains constant as a function of frequency, wouldn't that also impact phase coherency? Bifwynne, here is some more material for you to read that will address the phase coherency question you had yesterday (7/6/14): http://greenmountainaudio.com/speaker-time-phase-coherence/this is an article that Roy J wrote for Audio Ideas Guide back in 1997. A small cut & paste from this article: "The causes of phase distortion Time delay is the natural consequence of making something vibrate, whether it's electric fields or material objects. In speakers, only three things can cause time delays: ◾The moving elements (the drivers -- woofers, midranges, tweeters); ◾Their distances through the air to the listener; and ◾The crossover circuit. Let's go over the cause of motion-based time delays first. Different drivers (round, square, flat) have an inherent amount of phase shift, related only to each one's natural resonant frequency. One analogy is a weight hanging from a spring. If you move the other end of the spring up and down very slowly, the spring does not stretch and the weight follows your motion exactly. The phase shift between your applied force and the weight's motion is zero. The moving system is in a 'minimum-phase' mode. If you move more rapidly, the spring starts to stretch and contract -- and the weight no longer follows your driving force. It moves with a different phase. ......" there's a lot more to read but I believe that you should read the section "The Causes of Phase Distortion" to answer your question.... |
07-07-14: Bifwynne
Thanks again Bombaywalla. I caught the article. It doesn't speak to the impact of the speaker's electrical characteristics on phase coherence. I am totally confused here Bifwynne!! I don't understand your question - what do you mean by "the impact of the speaker's electrical characteristics on phase coherence"?? I've pointed you to Roy's article that talked about the impact of the electrical x-over on time-coherency. I've pointed you to Roy's article that talked about the impact of the driver construction on time-coherency. The x-over is the electrical part. the driver construction is the mechanical part. These 2 articles should have covered the info you were looking for..... |
Thanks for this info Psag. The DSP software definitely considers having phase & time-coherence as an important aspect of its signal processing so as to have cohesive sound. This should tell us something about the importance of time-coherence in speaker design :-)
Looks like DSP might be the way in the future... |
Short of outboard active crossovers, I'm starting to get the sense that mechanical (e.g., sloped baffles) and electrical (i.e., 1st order X-overs),.... cool, I like that! :-) I believe that the user community should demand more time-coherent speakers from the various manufs. Many people pay a pretty penny (incl you if you go the Magico-S route) for their resp. speakers & I really doubt that anybody wants to listen to added (speaker) distortion after having paid so much.... let us know what you discover about DEQX - like Ngjockey indicated, I doubt that DEQX is simply plug-n-play. I think that the user will have to know something about the physics behind the usage scenario (freq response, phase response, x-over slopes, phase coherency at x-over freq, amplitude of freq response at higher freq, etc) to bring out the best in DEQX. This is my guess. Meanwhile we will await word from you on this subject. Might want to start a new thread. Of course, do not forget to search the Audiogon & Audioasylum archives for existing chatter on DEQX - might give you a jump-start. Thanks. |
Hi Roy, good to note that you are back on this thread & have been kind enough to give us your time on this subject. Thanks! yes, I personally have looked at the waveforms (on the photobucket.com website) you pointed us to. I understand it much better now thanks to your recent post where you explained the diff between time-coherency & phase-coherency. I was looking at the waveforms but did not draw that conclusion; now I have! Also, the 2 cars & 2 cyclists analogy was very helpful. I have no particular question for you but I'm hoping that many other members who are on the fence re. time-coherence & others you are determined nay-sayers of time-coherence will take this opportunity of your being on this thread to ask their questions.... Bifwynne had a question re. the electrical properties of a driver & how that translated into distortion. Almarg enunciated the issue quite well & I've cut & paste his text below:
"Consider a simple two-way speaker having a first order crossover consisting of a capacitor in series with the tweeter, and an inductor in series with the woofer. For each driver that will result in well behaved 6 db/octave rolloff characteristics, which will result in time and phase coherence if other aspects of the design are also supportive, **IF** the impedances of the woofer and tweeter are purely resistive.
However I believe Bruce has been alluding to the fact that the impedances of the drivers are not purely resistive. And it would be more accurate (if still somewhat oversimplified) to electrically model them as consisting of a resistor and an inductor in series.
So the question then becomes: Doesn't the presence of that inductive component of the driver impedance (especially in the case of the tweeter) cause a deviation from first order 6 db/octave behavior? And if so, to a degree that may audibly compromise phase and time coherence? And if so, is that or can that be compensated for in other aspects of the speaker's design?"
Can you please address this question for us? thank you. (My understanding of this question was that the driver is resistive in its pass-band frequency range where its response is flat. I understood that it could be flat response in its pass-band only if it was linear i.e. resistive over that range of frequencies but I could be totally wrong). |
Consider a simple two-way speaker having a first order crossover consisting of a capacitor in series with the tweeter, and an inductor in series with the woofer. For each driver that will result in well behaved 6 db/octave rolloff characteristics, which will result in time and phase coherence if other aspects of the design are also supportive, **IF** the impedances of the woofer and tweeter are purely resistive.
However I believe Bruce has been alluding to the fact that the impedances of the drivers are not purely resistive. And it would be more accurate (if still somewhat oversimplified) to electrically model them as consisting of a resistor and an inductor in series.
So the question then becomes: Doesn't the presence of that inductive component of the driver impedance (especially in the case of the tweeter) cause a deviation from first order 6 db/octave behavior? And if so, to a degree that may audibly compromise phase and time coherence? And if so, is that or can that be compensated for in other aspects of the speaker's design? thanx to the above question posed by Bifwynne & well enunciated by Almarg, I did some research to try to understand what the issue might be. As I stated in my prev post, my understanding is that if the driver is used within its flat frequency response range of frequencies then that particular driver can be considered linear or purely resistive. And, some research seemed to indicated exactly that! Allow me to share: When Bifwynne asked the above question, I discovered that it took the me towards understanding the Thiel/Small (or T/S) parameters of loudspeaker drivers. There's much to learn here but that's a subject for another day. Some info that I thought is pertinent to this subject: There is a T/S parameter called Re (R-little-e) & a cut/paste from Wikipedia " Re Measured in ohms (Ω), this is the DC resistance (DCR) of the voice coil, best measured with the cone blocked, or prevented from moving or vibrating because otherwise the pickup of ambient sounds can cause the measurement to be unreliable. Re should not be confused with the rated driver impedance, Re can be tightly controlled by the manufacturer, while rated impedance values are often approximate at best.. American EIA standard RS-299A specifies that Re (or DCR) should be at least 80% of the rated driver impedance, so an 8-ohm rated driver should have a DC resistance of at least 6.4 ohms, and a 4-ohm unit should measure 3.2 ohms minimum. This standard is voluntary, and many 8 ohm drivers have resistances of ~5.5 ohms, and proportionally lower for lower rated impedances. " there's also a T/S parameter called Le (L-little-e) " Le Measured in millihenries (mH), this is the inductance of the voice coil. The coil is a lossy inductor, in part due to losses in the pole piece, so the apparent inductance changes with frequency. Large Le values limit the high frequency output of the driver and cause response changes near cutoff. Simple modeling software often neglects Le, and so does not include its consequences. Inductance varies with excursion because the voice coil moves relative to the polepiece, which acts as a sliding inductor core, increasing inductance on the inward stroke and decreasing it on the outward stroke in typical overhung coil arrangements. This inductance modulation is an important source of nonlinearity (distortion) in loudspeakers. Including a copper cap on the pole piece, or a copper shorting ring on it, can reduce the increase in impedance seen at higher frequencies in typical drivers, and also reduce the nonlinearity due to inductance modulation. " So, it looks like a significant source of distortion is due to voice-coil inductance modulation (variation) & not so much the fact that the voice-coil has actually a DC resistance associated with it (as Bifwynne & Almarg were thinking). So, how to tell when viewing/reading a driver's specifications that this inductance modulation is an issue? I don't really know but I took up Roy's advice to look at driver specs on Madisound. On the Madisound I randomly selected "Seas Prestige" - Seas makes good drivers, "Prestige" seems like its upper-end line. Here's the link to one of their 8" woofer drivers: http://www.madisoundspeakerstore.com/approx-8-woofers/seas-prestige-8-woofer-cd22rn4x-h1192 Lots of good info on this page but reading the specs might be Greek to most of us - I wanted to call your attention to the graph which shows SPL (left vertical axis) vs freq & impedance (right vertical axis) vs freq. From a Wikipedia page on Speaker Electrical Characterisitics I learnt ".....the effective electrical impedance of the speaker to be at its maximum at Fs, shown as Zmax in the graph. For frequencies just below resonance, the impedance rises rapidly as the frequency approaches Fs and is inductive in nature. At resonance, the impedance is purely resistive and beyond itas the impedance dropsit behaves capacitively. The impedance reaches a minimum value (Zmin) at some frequency where the behaviour is fairly (but not perfectly) resistive over some range. A speaker's rated or nominal impedance (Znom) is derived from this Zmin value (see below)." This Seas driver seems to have a 6.1 Ohms impedance at, say, 150Hz. Using the info from the Wikipedia site, the driver must be mostly resistive at 150Hz to give its minimum impedance at that frequency. Look at this driver's frequency response from 90Hz - 400Hz: practically ruler flat & look at the impedance variation over this same range - goes from 6.1 Ohms to 10 Ohms on both sides of 6.1Ohms, which is a small change in driver impedance compared to the change over the entire 20Hz-20KHz. The driver appears to be mostly resistive in this frequency range. I *think* the answer to Bifwynne's question is that if you use this driver in the 90Hz-400Hz range, you will get a mostly resistive driver whose impedance varies very little (between 6-10 Ohms), it's frequency response will be flat/linear & the phase distortion will be minimal meaning that the voice-coil inductance modulation/variation (which is a significant source of distortion) will be negligible. Roy, please correct me if I'm wrong. Thanks. |
07-17-14: Sounds_real_audio
Wouldn't it be easier just to tilt the speaker slightly backwards? tilting the speaker backwards attempts to merely align the acoustical centers of the drivers such that the sound from all the drivers reaches your ears at the same time. But what about the damage done by the higher-order x-over to the phase & time coherency of the music signal? This damage is the phase distortion that Roy is talking about all along. That cannot be corrected by merely tilting the speaker backwards.
I just want to listen to good music 'good' is a relative term - your music selection is best for your taste in music. Others might not find it 'good' at all... OR, did you mean 'good' as in well reproduced playback sonics?? |
Thanks Roy for the detailed explanation. :-) Was very helpful, as always.
OK, I wont put as much emphasis on the T/S parameters any more. I thought that I could read them & determine something about the quality of the driver. Not so, it seems.... |
Bifwynne, unfortunately all of the companies stated in Unsound's post do NOT still make time-coherent speakers. (John) Dunlavy quit making his speakers long time back & I believe that he, unfortunately, is not with us anymore (correct me if I'm wrong but that's what I remember reading in one thread). And, Meadowlark also does not make speakers anymore. Unfortunately there was something very unsavoury that went down w/ Pat McGinty (owner/designer of Meadowlark), his company & the location where he was making speakers. Audiomachina also does not make time-coherent speakers anymore. I was reading an old Meadowlark Osprey speaker review on enjoythemusic.com The Meadowlark Mantra
Three design principles underlie every Meadowlark loudspeaker: time coherence, first-order crossovers and transmission line bass............
McGinty argues articulately on his web site that time coherence is essential to long-term musical satisfaction and avoidance of listener fatigue.....
http://www.enjoythemusic.com/magazine/equipment/0204/meadowlarkosprey.htm link provided if anyone is interested in the full review. |
Bifwynne, Unsound, found this website of Meadowlark/Pat McGinty showing off all the Meadowlark speakers. I loved the looks of the Meadowlarks due to their superb wood finishes - always such a pleasure to see! http://www.patmcginty.com/index.html |
Hey guys I found this wonderful, very simple, animated essay from Pat McGinty (of Meadowlark) explaining time-coherence (in which he believed sincerely). Please read this (in the beginning he goes off the deep end relating the birth of the stars to time-coherence but please bear with him - he's trying to make a point: http://www.patmcginty.com/Dbench2.htm |
You are right Unsound, Audiomachina's website seems to be up-to-date (I saw one post dated June 9, 2014) so it seems that they are alive & well producing time-coherent speakers. Thanx for the correction. And, BTW, you guys have to read these "Pearls" (of speaker deisgn) from the owner/designer of Audiomachina speakers - esp. for determined naysayers. These notes echo practically 100% what Roy Johnson has been trying to educate us with since 2002 when that time-coherence thread started by RBischoff appeared on Audiogon. Just like Roy's texts, this essay on speaker design is very well written (& I can see time & again the points that Roy has tried to drive home into us re. 1st order x-overs & time-coherence) - a superb & easy read: http://audiomachina.com/pearls/ |
In light of Roy's feedback to the sound.westhost.com material, here is (what seems) a much better website to read up on quadrature signals. The article deals with complex signals but it is not complicated - the graphics make it much easier to understand. if you don't want to read the article, scroll to Fig 10 directly & you will see why 2 signals in quadrature (i.e. separated by 90 degrees of phase) add up to a constant i.e. adding 2 signals in quadrature does not give you another signal; rather it gives you a scalar/just a number. As Roy was saying earlier on - this can happen ONLY with a 1st order cross-over where the phase difference between tweeter-mid, mid-woofer is 90 degrees & when these signals add up at the listener's ear they appear as tho' there was no additional delay thru the x-over. http://www.dsprelated.com/showarticle/192.php |
Why not DEQX?
Bifwynne
Bifwynne,Roy has already answered your question some time back on this page 4. Did you miss reading it?? Here's a cut & paste from his 7/16/14 post: Bifwynne,
DEQX seems fine in theory, and certainly makes a positive difference. For me, it has serious limitations because it cannot measure exactly what needs to be corrected. This leads to results that depend on the music being played and sometimes a limitation in one's seating position.
In particular, DEQX cannot see the immediate reflections from the cabinet surface surrounding the tweeter. It cannot correct properly for anything happening below middle C because of floor-bounce effects on the microphone are not the same as they are to our ears on music.
There are other issues, but to me, those are the two largest ones. I find that a much higher level of coherence is achievable passively. here's more info from Roy on DEQX in his 7/17/14 psot to the whole group This varying time-delay is what DEQX-type components are trying to correct, and what regular digital crossover circuits never attempt to correct (offering only fixed time delays, such as one millisecond). To correct the varying time delay, a heck of a computer is required, hence the high cost of DEQX type of gear.
Measurement issues and limitations still confuse DEQX type of gear, for two reasons- we cannot (yet) program that computer to how we actually hear on music, and that a measurement microphone cannot resolve the (countless) reflections off the front of a cabinet. If I had spent money on a DEQX, I would first place an "F-11" pure wool felt all around the tweeter, and then run the calibration routine.
Best,
Roy more info on why DEQX has limitations from Roy's 7/19/14 post: Putting the measuring mic for DEQX up close to a speaker is pointless (except for fixing up a subwoofer), as what the mic would then be hearing is coming from drivers at much different path-length-differences to the mic compared to the path-lengths to an ear ten feet away. We all know how walking up to a speaker changes everything we hear. Perhaps they are suggesting this for fixing one driver at a time. That has problems too, because any driver's tone balance is different at ten feet away vs. ten inches away. Bifwynne, this is plenty of info for you to understand why DEQX has limitations & is not a panacea for time-INcoherent speakers. Don't you think? |
Lewinskih01, I took the time to read the XO White Paper by Dr. Uli. In many places he makes the same points that Roy is making i.e. lower order x-over ckts are better than higher order x-over ckts. He talks about the time delays getting worse with higher order x-over ckts - same point that Roy has made many times. Dr. Uli talks about using minimum phase filters for the analog x-overs & using linear phase filters (which are digital FIR filters. there is no equivalent in the analog domain) for his Acourate digital x-over software. Dr. Uli makes a general statement that low-order minimum phase filters used in analog x-overs have limitations & create time distortions & cannot be used...... BUT he conveniently starts off with a 2nd-order x-over ckt while completely glossing over a 1st-order x-over ckt. Does the 1st-order x-over ckt have the same limitations as the 2nd-order x-over Dr. Uli discussed? Dr. Uli would like you to think so but I don't think so...... I created a simple 1-order network for a tweeter, midrange & woofer. I assumed a 6 Ohms resistance for each of the 3 drivers (totally arbitrary). I arbitrarily chose x-over frequencies of 300Hz & 2KHz. I simulated the frequency, phase & step responses of this 1-order x-over. I've labeled the curves in each of the 3 graphs so you can see which curve belongs to which driver. I've also put markers on various curves so you can see the phase shift at the x-over frequency. For the frequency response - look at the sum of the frequency responses. There's only a 2dB hump at the x-over points. For the phase response - look at the sum of all the phase responses/ There's a phase shift of only +/- 8 degrees over the entire audio band of 20Hz - 20KHz. And, for the step response - you can clearly see that all 3 drivers act in unison to create unified step response (rather than the spikes you see in time-Incoherent speakers where the tweeter acts first, the mid second & the woofer third). From these simulations, a 1st-order passive x-over looks quite good. And, I don't have the music signal going thru somebody's DSP algorithm which is doing a great deal of signal processing to massage the music signal thereby imparting its sonic signature to the music signal. Sure the passive x-over components are also imparting their signature to the music signal but by using top quality components I can minimize this. In the DSP software, if I don't know what I'm doing, I can botch thing pretty badly because the music signal is so heavily modified by the DSP algorithm. Here is the link to the simulations, if anyone is interested: https://picasaweb.google.com/bombaywalla9/FirstOrderXOverFreqPhaseStepResponses?authkey=Gv1sRgCOz6xv6RnMDeUA#In the XO White Paper, Dr. Uli says that "So the crossover has to be selected so that the good properties of the driver are used ! If the driver does not have a good behaviour we should not use it." I am assuming the "good properties" of a driver are that it has flat freq response over its passband & rolls off at a frequency beyond the x-over freq chosen in Acourate by the user. BUT............ The degree that Acourate can compensate for any driver depends on how well you can characterize the driver. And, we of course, do not know if the drivers in our existing speakers have these "good properties" or not..... |
hi Lewinskih01,
yes, with some engineering proof, that's what I was trying to say. And, the reason that seemed to make sense to me is that signal processing is happening correctly, real-time thru the passive x-over components without any intervention by a human-being. In a time-coherent loudspeaker with passive x-overs, drivers with "good properties" have already been selected & the x-over designed around them & the whole system would be working to benefit the user.
With digital x-overs the correction is as good as the skill of the user to characterize the drivers & to come up with the appropriate filter response to yield a time-coherent delivery. And, from reading Roy's letter to Six Moons - the link to which he provided earlier on - it's no easy feat to characterize a driver in the room. One cannot use 1 type of test tone, one needs to use many different types. And, one needs to measure the driver response in many ways to get an accurate characterization of the driver. Otherwise, the DEQX or Acourate correction will be (very) limited leading to less than stellar benefits.
I don't think that Roy can tell you how well DEQX or Acourate will solve your problem because the answer lies in how skilled you are in understanding the science behind how the driver response is affected by your room,
how skilled you are in DSP algorithms to come up with a filter that corrects for your room & your particular choice of drivers
how skilled you are in understanding the science behind reflections of drivers off the front baffle,
how skilled you are in understanding what the requirements are for selecting a microphone to do the driver characterization,
how skilled you are in compensating for this mic's own frequency response so that you don't misunderstand the mic's response to be that of your driver's,
etc, etc.
My understanding is that if you room correct like HT Receivers do & plug in the correction into some pre-designed filter in the software, you'll get a correction that's average at best & you might not like the results.
The thing that Roy has been saying all along is that we don't listen to test tones (which is what the room correction tones are) - we listen to music which is a bunch of partial wavelengths of various frequencies.
You use full cycle tones to characterize the driver then do the correction & then play partial wavelengths of various frequencies thru that driver - the correction to the driver, in my understanding, is invalid.
Of course, I could be totally off-base here....
FWIW. |
