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. |
Prez-
Here is an anonymous contribution sent to me by a horn enthusiast. I hope it provides some clarification.
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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.
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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. |
"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. |
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. |
"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. |
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! |
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 =;) |
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. |
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. |
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. |
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. |
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. |
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. |
"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! |
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. |
Its funny reading some of these comments. I wonder if some people just say what they read in a audiophile magazine. |
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? |
He apparently has ears and has listened to a lot of stuff.
The same credentials as most of us I would say. |
Mapman, what makes it a "credible source"? |
"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. |
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. |
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. |
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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 |
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. |
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. |
"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. |
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.) |
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! |
"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? |
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. |
"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.
|
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. |
Prdprez, John Dunlavy also thought the step response was the most important measurement. |
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!! |
Po-Tay-To = Po-Tah-To
Let's call the whole thing off. |
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. . |
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? |
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.......... |
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 |
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 |
Herman, there certainly has been much debate over the merits of time coherency.
Just to clarify one point first. The way they describe it, time "coherent" demands time "alignment". But the reverse is not true.
You're point about phase is certainly correct. But I think there is also a distinction with the "when" of phase. For instance, it's either the 2nd order or 4th order filter (I can't remember which) that is phase coherent in the crossover region. Which is to say, all the peaks and valley's line up. 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.
The easiest way I found to grasp it was to note that TIME coherent was at the pinnacle of the hierarchy. Indeed, most people, when refereing to this type of design, say "Time AND phase coherent". But it's redundant to say that since time coherent demands phase coherent. It demands both time alignment and phase alignment. These other two could be achieved individually by means of physical placement or filter makeup. But both, on their own, was only part of the story. Anyway, thats the best way I know to describe it.
Also, I think phase alignment and coherent ARE the same thing. But I'll have to think about that a little more to be sure. No, I think its true. anyway..........
First order filters do have phase shifting but the filter circuit as a whole compensates. The current lag in an inductor is the same degree (hopefully) as the voltage lag in a capacitor. But, I'm going to have to think about that some more before I try to go any further. I want to make sure I don't mistate anything.
The one measurement that is the arbiter of all this is the acoustical step resonse. Two speakers that easily show this is Wilson and Dunlavy. Both are time "aligned".
Wilson: http://www.stereophile.com/floorloudspeakers/920/index6.html
Dunlavy: http://www.stereophile.com/floorloudspeakers/162/index10.html
Looking at the step responses. Though, be careful when reading what JA has to say. I've noticed that over the years he throws all the descriptions around without much measure of consistency.
The short of it is this. The only speaker design that shows a step response (and therefor the most accuracy in the time domain) that mimics the input is a "time coherent" design. Ala Dunlavy, Vandersteen, Meadowlark, etc etc. They are the only ones that approach the right triangle form.
The merits of this? Well, like I said, Hotly debated.
I gotta run. More later.
Cheers! |
"Mapman, I'm not sure that Ohm's current non-bending wave non-Walsh drivers qualify."
I guess you'd have to take that up with John Strohbeen to know for sure. |
Mapman, I'm not sure that Ohm's current non-bending wave non-Walsh drivers qualify. |
Prez, I hear what you are saying but I think the manufacturers are using terminology to confuse the layman in an attempt to carve out a unique slot in the marketplace. In other words, marketing BS. A change in arrival time is a change in phase no matter how it is done. They are synonymous. If you read Thiels papers they admit as much. Either the different frequencies arrive at the ear with the same timing relationship they had when they were put on the recording or they do not. If not it could be that the drivers aren't aligned, That a digital or electronic delay was employed, or there is a phase shift through some reactive device like a crossover. If they want to distinguish phase shifts caused by crossovers as phase coherency since they are frequency dependent and those caused by driver alignment as time coherency since they are not frequency dependent I'm on board with that, but time alignment and time coherency are the same thing. By eliminating all reactive components after my amps (no crossover what so ever) and implementing the crossovers digitally before the amps I should only have phase shifts caused by the reactance in the drivers and hopefully the bulk of that is outside the band of frequencies they will be fed.. Each band can also be digitally shifted in time so they should be close to being time and phase coherent to use Thiel's terminology. The purists cringe when you talk about digital processing but so far so good. One point of clarification, Even first order filters cause phase shift as you approach the cutoff frequency. Thiel claims that they have achieved equal but opposite shifts from the drivers above and below the cutoff so they cancel. The phase shift is kept low by using very gradual (6 dB/octave) roll-off slopes which produce a phase lag of 45° for the low frequency driver and a phase lead of 45° for the high frequency driver at the crossover point. Because the phase shift of each driver is much less than 90° and is equal and opposite, their outputs combine to produce a system output with no phase shift and perfect transient response. I'm still trying to wrap my head around that one. If one driver produces a sound shifted in time so it occurs slightly earlier than those in the passband and another produces the same sound slightly later how can that add up to no time change? . |
Cdc - I'm not well schooled in the matters you brought up just now but my sense is that you are demonstrating that an Aveo gets decidedly better mpg. than a Corvette. Of course, you are right but the parameters qualify the argument.
I recall you mentioning earlier that you listen at 65 db. Probably the areas where you find your single driver to excel are dependent on keeping the SPLs down. My average listening level is more like 85 db (still not very loud) and I suspect your single driver might keep up at that level in a small enough room. Mr.decibel would not get much of a bang from that approach, however, because he says he listens at upwards of 100 db., though I can't imagine how.
So, while specifications are very useful, even essential, they are dependent on circumstances and conditions that don't always appear on the stat sheet.
I'm pretty tempted by the logic and testimonials I read about with single drivers but I can't see them as a realistic replacement for my horns. |
Cool! Thanks Mapman.
Ima check that out. |
Even single driver speakers are not perfectly time and phase coherent. But close enough** to trick us into thinking they are.
** Subject to debate. |
