If you are a full wavelength behind, wouldn't that make you 360 degrees out of phase?
It would also seem logical that "out of phase" signals, regardless of cause, are less of an issue for longer wavelengths than for higher frequency discrepancies. In my case, there is no crossover of any type or description, real or imagined, above 300 hz. At the crossover point I have a wavelength of 45 inches. I correct for the 16 inches of front to rear positioning between my drivers by utilizing a half meter of time delay in my DBX. I'm not sure the difference would be very audible though. |
Different / Better example........
Herman, here is a different example of a speaker that is "time aligned" but with a high order crossover. (Linkwitz/Riley I believe.)
All of the drivers are in the same polarity as well. It's easier to see the delay that the crossover imposes. But I think (dont hold me to this) it IS phase aligned.
http://www.stereophile.com/floorloudspeakers/699hales/index4.html |
Macrojack, YES, that is the precise way to describe it. It is 360degrees out of phase. But if you take a snapshot in time and look at the waveform (sine waves show this best, obviously) it LOOKS like it is aligned because all of the peaks and valleys matchup.
And herein is where the marketing BS starts to really get out of control. Well, in one manner anyway.
I'm still trying to find the place on the web that helped me the most in understanding how first order filters result in zero phase shift. Haven't found it yet.......... |
Mapaman, I'm not the one making the claims. Ohm's web site makes some claims using some audio buzz words, but, they don't seem to be used correctly. Perhaps some evidence to support those claims might be appropriate? |
The difference is that some frequencies started before others. The delayed ones are a full cycle behind. They are still phase coherent but not time coherent. It's not that simple. What you describe can only apply to steady state sine waves. Music is a complex wave with many frequencies starting and stopping and varying in amplitude. Different frequencies get shifted different amounts as they get rolled off so they don't line up like the original. They are not phase coherent. I still say time alignment = time coherent. I've seen no evidence to the contrary. . |
Po-Tay-To = Po-Tah-To
Let's call the whole thing off. |
Exactly Herman! What you've stated is the crux of the argument FOR time coherence. What I stated is the over simplified reasoning given by designers who use steep filters.
They point to "phase coherence" but the only thing they are measuring is sine waves.
As far as "alignment" versus "coherent" go, well, maybe just semantics. Thats fine. I'll go just one step further using a different explanation from another designer and then let it be. Because to each their own.
Anyway. This is how Pat McGinty basically explained the difference in his mind.
Take two drivers, a tweeter and a midrange and you mount them on a flat baffle. Connect the positive leads together and the negative leads together. Take a 9V battery and tap the leads against the battery. The microphone will see two distinct upward spikes. (assuming you touched positive to positive, etc.) Then you start to slant the baffle backwards an increment and repeat the battery test. The result is that the spikes will converge a little bit because the acoustic center of the tweeter physically leads the midrange and, assuming the tweeter is on top, the more you slant it backwards the more the tweeters acoustic center moves backwards towards the acoustic center of the midrange. Perpendicular to the horizon is the frame of reference here.
Anyway, at some point the microphone will see one convergent spike. This is what they consider the physical time alignment of the two speakers. And this was basically the first step of the design process used by Meadowlark, once they decided on the drivers they were going to use.
So at this point the drivers acoustic centers are aligned at the precise point in space that the microphone sees them as one.
So if you now apply a good and appropriate first order filter to the drivers you should end up with a fairly accurate step response. This is what they consider time coherent because it is the only way that all frequencies arrive at the microphone (or ear) at exactly the same time. And, actually, Meadowlark's were pretty good at this.
But, if you applied a fourth order filter as was the case with the Hales Transcendence Five speaker that I referenced. (And also once owned) you end up with a step response like what you see in the Stereophile article. If you bypassed the crossover in those Hales and set up a microphone at a normal listening level at a normal listening distance and applied the 9V battery test (Note: you aren't trying to pass DC through the drivers, only create a "tick" response by quickly touching the leads) you would see a single spike from all the "ticks" arriving at the same time.
But you pass music through the steep crossover on the way to those same drivers and what happens is that, because of the steep filter, you see the tweeter lead the mid, and the mid lead the woofer. In this case the acoustic centers of each driver are time "aligned" but the speaker is not time "coherent".
Anyway, as I said, these are the distinctions that Time Coherent designers make. And, like Pat McGinty always said, "All you really need to do is look at the step resonse because if that isnt right then nothing else matters." And, for better or worse, these were the decisions and distinctions these guys made. The fact that there are so few who make speakers like this is a very loud statement as to the importance the industry as a whole grants these principles.
Cheers!! |
Prdprez, John Dunlavy also thought the step response was the most important measurement. |
Unsound, ALL time coherent designers think/thought this. Vandersteen, Thiel, Johnson, etc.
It is the single measurement that most distinctly shows the output signal as it relates to time. And timing was the paramount issue for all of these guys. |
"Perhaps some evidence to support those claims might be appropriate? "
Perhaps.
The OHMs seem to work and sound as claimed as best I can tell. I see no evidence to indicate false advertising or other less than honest business practices.
Also I am sure most OHM customers don't care about technical details. Listening is all the proof that really matters.
Again, if you have questions regarding the technology, best to address them to the man who knows the answers, John Strohbeen. I'm always interested to hear what John says. I find it almost always understated but accurate.
|
Again, I'm not the one making the claims. |
I wonder if John Bau gave this matter any thought when he created the Spica TC-50? When was that, like 1982? |
"Again, I'm not the one making the claims"
No, but you are questioning them. All vendors make claims. If you have questions, you should ask and get the answers.
I believe the claims to be true based on what I know of the design and what I hear. But that does not prove anything especially to a skeptic now does it? |
Macrojack,
Those TC-50s are notorious for showing up in any discussion of time coherence. They've become practically an iconic item in the discussion.
Because they used a first order filter on the mid/woofer driver and had that distinctive slanted baffle it is often assumed that they were time coherent.
Stereophile measured the speaker before they obtained the MLSSA system so some of the measurements related to time were not available.
However, it has since been shown that they are not time coherent. It is estimated that they sounded so damn good because the primary driver handling the midrange was using a first order filter and therefor had a very nice impulse response, which the old stereophile measurements DO show.
Cheers! |
Also, Macrojack, John Dunlavy was known for claiming that his later Dunlavy Audio Labs speakers were superior to his earlier Duntech designs precisely because the "new" (at the time) MLSSA system gave him the opportunity to measure far more precisely and implement his theories to a greater degree.
This was late '93, early '94.
Anyway, back to horns!!! (didnt want to hijack this thread, haha.) |
"Another thing that makes the Ohm speakers unique (then and now) is that they are almost a 1-way speaker. The CLS driver handles frequencies from the bass through about 10kHz, at which time they (finally) hand off to a (metal) dome tweeter. In doing so, they remain completely free of all known deleterious effects of crossovers usually located in the all-important midrange. Coherence is the natural by-product of one driver doing most of the talking - or singing as it were. So are phase coherence and time alignment."
This quote from a six moons review of one of the OHM Walsh designs pretty much states the case for the OHM CLS driver achieving a high degree of coherency in that a single driver handles all but the uppermost frequencies. I think this is an established fact regarding the OHM CLSs in that it has been reported in many reviews over the years and never brought into question or challenged at least in any reputable publication I know of. |
Mapman, the original Ohms Walsh driver was not a one way speaker, there were different segments. Though it might not have used an electrical cross-over, there were indeed mechanical cross-overs. Still a brilliant idea, that I think might has been improved upon by the German Physiks DDD, which appears to be a single driver. I think we're getting off topic now. |
OK, back on topic, German Physiks has a model that attempts to achieve full range with the DDD driver by horn loading it called the Unicorn.
Has anybody ever heard these? I always found a horn loaded Walsh driver to be a quite unique concept. |
Here's a thread from last year that might shed some light on the subject. Please note the same few people chiming in then as now in behalf of horns. That indicates to me the need for a broader base of knowledge on the subject.Too few audiophiles are aware of the performance potential locked up in this technology.
http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1238177483&openfrom&17&4 |
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Mapman, those horn loaded German Physiks are at the lower end of the line for German Physiks. Their top tier products don't use horns. As for the reviewer, I have no idea who he is, but he's entitled to his opinion. |
Macrojack, that link seems have started with regard to a driver, not horns in particular, though it did seem to drift there, at least in part to you.
A few audiophiles are unaware of the performance limitations locked up in this technology. |
"he's entitled to his opinion"
Yes, opinions are opinions but for any somewhat credible source to indicate that $1000 low end speakers from one line can match $21000 lower end models from another and higher end models selling for only a few thousand more outperform the $21000 speakers using a similar technology in every way is an eye opener that at least has to make one take notice. |
Mapman, what makes it a "credible source"? |
He apparently has ears and has listened to a lot of stuff.
The same credentials as most of us I would say. |
He also indicates he is "a longtime proponent and user of Walsh speaker technology".
And he indicates he writes a syndicated consumer electronics column. So he is apparently a (gasp) journalist!
So much for credibility? |
Its funny reading some of these comments. I wonder if some people just say what they read in a audiophile magazine. |
Sthomas - I agree. Probably. Can you elaborate as to what comments are funny and why?
re: Walsh drivers in horns, I know nothing about the credibility of the reviewer but I do know that German Physics is a legitimate and highly credible manufacturer who is unlikely to market a product that is utterly without merit. We should probably withhold judgement until we have actually heard them.
I don't think it sounds too promising but I have no grounds for such a presumption. I'm not an expert on horns. |
"German Physics is a legitimate and highly credible manufacturer who is unlikely to market a product that is utterly without merit."
I would not say that. The $1000 speakers are quite good (similar to design to the Walshes in my system but smaller) and have garnered a nice following. If teh GPs sound as good, then that has merit. They are just 20X as expensive, so not much merit there.
Stthomas, I can assure you that I do more than just say what I read. I read to help learn. I do not discredit anyone or anything without basis. I tend to give most the benefit of the doubt that they have some information of value to share until I determine otherwise.
Best to keep an open mind in general! |
BTW, I was quite disappointed to read Mr. Lindich's findings regarding the GP Uncorns in that I am a big fan of Walsh technology and I do believe horns have the potential to break certain common performance barriers as well, so my expectations for a design using both in a single driver full range design were quite high.
That's why I'm wondering if anybody on this thread can offer any insight to how the Unicorns sound. I've never heard them but am intimately familiar with the OHMs. No other speaker has lured me away from them during 30 years of ownership of various models. The GPs are one that I would expect could (if I could afford them) and the application of the horn with teh Walsh is certainly quite unique at a minimum.
A poor setup at a show is always suspect. The Unicorns apply equalization to the bass as well, so who's to say this was set to match Mr. Lindich's preferences. |
One other thing that struck me is that despite being horn loaded, the Unicorn is still only 87 db or so efficient, according to the specs I found. A horn loaded speaker that is still that inefficient is certainly a unique beast as well. |
I suspect that GP's Unicorn was an exercise in trying to make a full range single driver speaker system. As appealing as that concept might be, success in that quest has been allusive for all that have dared to try. The idea of a horn loaded omni directional driver would appear to be an oxymoron. |
Yes horns and omni drivers are a unique combo for sure.
Most GP designs appear to limit the coverage of the DDD driver to the upper frequencies where Walsh drivers operate in a mostly wave bending manner, as I understand it. This is supplemented by more traditional dynamic drivers for the low end.
The Unicorn apparently trys to extend the range of the DDD lower where it like all Walshes I believe operate more pistonically in producing bass, but that does not appear to be the strength of the DDD. The horn loading and equalization applied in the Unicorn to the DDD bass region output appears to compensate for that. |
Macrojack, my 4.5" drivers are only good to 70-75dB because I run them full range from 45-15,000hz. If they were cut at 300hz like your horns, they could be played over 100dB. If you go with Folded transmission line or Standard transmission line they advertise that you can get the bass and volume levels. I believe this Tang-Band W4-1337SD will give similar performance to your horns. I have used it in a cabinet as small as 8 1/2" high. You will loose some bass as compared to a larger cabinet but if you put them against the wall, you should be okay. I found the HF ttshhh ttshh, annoying and would require a low-pass filter to cut or reduce the HF. I also prefer the snappy, softer sound of paper to the crystalline clarity of titanium. But I also use bi-polar solid state amplification and CD's. There are many good single drivers (so I am told). Especially the PHY and Supravox if you are willing to spend the money. Also Jordan JX-92S but I found them to be thin in the bass. Even with a large transmission line cabinet. Hope this clarifies things for you. |
Mapman, the DDD appears to be full range till it reaches well into the bass region. After that the DDD driver would need to be augmented with a woofer/sub-woofer for full range classification. Those lower frequencies have less apparent directional ques, and probably maintain the illusion of omni directional presentation well. Keeping the cross-over away from alternate drivers at higher frequencies where our ears are most sensitive and usually are have the narrowest directivity would seem to be preferable. Again the DDD doesn't have the mechanical cross-overs that the original Walsh driver had. Of course the catch is; they're pretty darn expensive. |
Yes horns and omni drivers are a unique combo for sure. I've heard an omni-horn system. Sits on top of the local firehouse. Very clear, loud sound, but only one frequency. THAT gets boring in a hurry =;) |
I have a question for the horn guys.
A complex musical signal has both compression and rarification components of it's pressure wave. I can see how the compression component interacts with the horn.
How does the rarification component react with it, if at all?
Thanks! |
"Again the DDD doesn't have the mechanical cross-overs that the original Walsh driver had. Of course the catch is; they're pretty darn expensive."
no, but with teh exception of the Unicorn, it is not full range and supplemental drivers with electronic crossover are used.
I suspect the "mechanical crossover" of the original Walsh behaves better from a coherency perspective in that crossovers tend to work against coherency in general it seems.
DDD covers higher and mid frequencies and crosses over toward the low end of the audio spectrum. OHM CLS covers lower and mid frequencies and crosses over higher (about 10khz I believe). Most, particularly as they age into their 40s or so, cannot hear above 14 khz or so, so that is the argument for the CLS approach.
All Walsh drivers operate via wave bending at higher frequencies and transition gradually to more pistonic motion to produce lower frequencies. That would indicate DDD produces more frequencies using wave bending than OHM and OHM more using pistonic motion to cover bass, however my understanding is that both apply the Walsh driver principle however differently in these ways. That is how it has been explained to me.
So we all can chose our preferred designs and sounds. OHMs in general will cost a lot less than GP however, that much seems certain. |
Mapman, the original Walsh Drivers had 2 such mechanical cross-overs. I suspect that there was some cross-over in the lower than the extreme upper frequencies as well. The DDD doesn't have any such mechanical cross-overs. |
"Mapman, the original Walsh Drivers had 2 such mechanical cross-overs. I suspect that there was some cross-over in the lower than the extreme upper frequencies as well."
That is correct the original OHM Walsh drivers used three distinct sections for low, mid, and high end that resulted in two physical equivalents of a "crossover" between sections, though I would not equate these "physical crossovers" to electronic ones in regards to how they behave, particularly in regards to coherence.
"The DDD doesn't have any such mechanical cross-overs"
That is correct also, though an external electronic crossover and non walsh bass driver is used for full range in most GPs.
In the case of the OHM CLS, the Walsh driver, crossover, and tweeter are all considered part of the full range "CLS" driver.
In either GP or OHM case, for full range, with exception of the GP Unicorn, two drivers and a crossover are used. |
Prez-
Here is an anonymous contribution sent to me by a horn enthusiast. I hope it provides some clarification.
----------------------------
I am not an expert on this but, when the sound forms in a pipe, and it leaves the end or "mouth, it becomes mainly a refraction wave. At the throat it is a pressure wave
Due to an 180 degree phase shift , there is an abrupt drop in pressure at the end of the tube, and the wave is reflected back down the horn, and the cycle repeats itself.
But, if the tube is made into a horn shape the pressure drop is not nearly as intense at the mouth, and the refraction wave is diminished so only a small portion of it reflects back down the horn. The throat of the horn is a High pressure wave.
-----------------------------------
More from the same source:
from.....http://www.physicsclassroom.com/class/sound/u11l3d.cfm
Refraction of Sound Waves
Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. So if the medium (and its properties) are changed, the speed of the waves are changed. Thus, waves passing from one medium to another will undergo refraction. |
One last point on the horn loaded Walsh driver used in the German Physiks Unicorn.
The increasingly pistonic operation of the DDD Walsh driver towards the lower end of the sound spectrum is what would produce the pressurization at the mouth needed to enable a horn to be used with a Walsh driver. The horn would not be exposed to sound pressure emitted orthogonally via wave bending in the Walsh driver, so I am pretty sure wave bending alone could not work with a traditional horn design. |
Mapman, I won't argue the point of how the GP Unicorn works, but as long as the sound is emitting from a source, I suspect once could attach (a) horn(s) to it, if that's what they wanted to do. Though it would seem to be a contradiction of philosophies in this case. |
Ok, enough beating a dead unicorn.
Ha Ha Ha! Dead unicorn, a horse with a horn, get it? |
I'm afraid I do get it.:-) |
Thanks Macrojack. That was very helpful. |
Delighted to be of assistance. |
Somebody out there likes horns besides me.
Bill Woods is so busy he has had to stop taking new orders until he can catch up.
And as an aside, here's a very interesting speaker that will challenge a lot of beliefs and assumptions:
http://www.yorkville.com/products.asp?cat=38&id=268&type=29
These will be a downgrade cosmetically for nearly everyone but an upgrade for most people in terms of sound. Not suitable for intimate settings, however. They are big and sound bigger. Reports from seasoned audiophiles are uniformly positive. |
Here's a testimonial for the Unity Horn when it was available through DIY channels:
http://www.cowanaudio.com/unity.html
Here's a source randomly chosen from a Google search:
http://www.musiciansbuy.com/YORKVILLE-U215-SPEAKER-CABINET.html
I urge all of you to do your own searches to learn more about this option. The pricing exposes high end audio for the rip off that it is. |
"but an upgrade for most people in terms of sound."
In what way and based on what?
You are not just saying that because it uses a horn, are you? |
