There is another thread about this under speakers here on this sight. It had 151 posts last time I looked. It started off with what speakers are actually phase and timed aligned. The true contenders were Theil, Dunlavey and Vandersteen's. The discussion then took off to what was better and all the misconceptions about this subject.
Anyway, I for one am a beleiver in using a speaker that tries to be phase and time aligned.
That's cool Bigtee ...just like some believe in ported,nonported,TL and everything in between.I know about the other thread just found another person with a different perspective .Just wanted to know what others think about his claims.
Get rid of the multiple drivers and dividing networks and then you have a time and phase coherent speaker. I'm sure that at least Twl and Karls will give me a big "AMEN" on that one : )
If you've done the testing and have documented your results, you should not be afraid to name the specific makes and models that are falsely advertised. I'm sure that there are those there that would love to read your notes. Given that Stereophile tests for such things, it would be interesting to see how your results jive with theirs. That is, if the two of you have actually tested the same models. Sean
I may be over-simplifying this (I tend to do that from time to time), but all of the physical descriptions of how dynamic drivers react to increasing frequencies, and the resulting distortions, seems to make a good argument for electrostatic panels. With an electrostat, the diaphragm is driven over it's entire surface, instead of just at the perimeter of the voice coil, it has extremely low mass, and the crossover from the panel to the woofer ( in hybrid models) occurs below the mid-range frequency band.
Are Time and Phase alignment essentially non-issues with electrostatic speakers?
Sean, I must respectfully disagree. Most full range driver systems are not at all phase coherent. The reason is that most of these systems use drivers in the 3" to 6" range. When reproducing high frequencies these drivers begin to give up pistonic motion, the surface of the cone rippleing, just as when you see a pebble thrown into a pool of water. FFT analysis will show this. As the cone gives up pistonic motion the high frequencies travel down the length of the cone rather than at a 90 degree angle. But, in fact, this is a good thing. Although phase response is traded within the driver itself, what is gained is much better dispersion. The driver acting as though it is much smaller in diameter than it really is. Even so, beaming is still problematic in these systems. The Lowther even uses a whizzer cone, like the old Phillips midranges, which, though it aids dispersion, again hurts phase response as the high frequencies travel down the length of the whizzer rather than being produced at right angle to the cone. This too is classic breakup. This is not to say that these systems cannot sound great and avoiding the violence done to the signal by crossovers and multiple drivers gives a powerful coherence. But single driver systems using cone drivers cannot produce a decent representation of a square wave. If one looks to other technologies, such as Quads ESL63 you can find a single driver system that passes an almost perfect square wave. One could argue though that the delay line and series of annular rings are at least as complex as most crossovers. The closest we can probably get right now is with headphones.
Sean, I must respectfully disagree. Most full range driver systems are not at all phase coherent. The reason is that most of these systems use drivers in the 3" to 6" range. When reproducing high frequencies these drivers begin to give up pistonic motion, the surface of the cone rippleing, just as when you see a pebble thrown into a pool of water. FFT analysis will show this. As the cone gives up pistonic motion the high frequencies travel down the length of the cone rather than at a 90 degree angle. But, in fact, this is a good thing. Although phase response is traded within the driver itself, what is gained is much better dispersion. The driver acting as though it is much smaller in diameter than it really is. Even so, beaming is still problematic in these systems. The Lowther even uses a whizzer cone, like the old Phillips midranges, which, though it aids dispersion, again hurts phase response as the high frequencies travel down the lenght of the whizzer rather than being produced at right angle to the cone. This too is classic breakup. This is not to say that these systems cannot sound great and avoiding the violence done to the signal by crossovers and multiple drivers gives a powerful coherence. But single driver systems using cone drivers cannot produce a decent representation of a square wave. If one looks to other technologies, such as Quads ESL63 you can find a single driver system that passes an almost perfect square wave. One could argue though that the delay line and series of annular rings are at least as complex as most crossovers. The closest we can probably get right now is with headphones.
Crap, now I'm posting in stereo. I must not be too coherent either. My appologies.
All sound eminates from a point source at the same time and in the same phase. This is the very basis of operation of the Walsh series drivers and why they do some things like no other dynamic driver can.
A true point source driver might not have linear distortion characteristics across the entire band that it is trying to reproduce, but it will do some things VERY right. The biggest problems that we run into with such drivers are with driver mass, excursion capabilities, dispersion, maximum SPL and damping of the driver itself. Since we are limited in technology at this point in time, we can't expect to get everything all at once and not have a few bills to pay along the way.
I do agree that drivers using whizzer cones have their own problems. In effect, you have two cones being driven from one motor. What you end up with is two distinct frequency ranges, radiation patterns and the effects of cancellation between them, which somewhat defeats the purpose of using a single driver operating full range. Sean
Go to www.madisound.com and go to the forum section.
All arguements about all things speakers, building, and of course the phase arguement are all there.
If the speaker is coherent at the X/O point that's awesome, and if it varies from that point, then hey it's a normal transducer. The all do it. Usally several times. IF you had measured the drives on an AES baffle you would know this.
I haven't measure 700 driver but I have measured over a 100 on and to this day I have yet to find a single driver that doesn't go through at least 1 cycle of phase inversion from what ever is inteded hz to whatever is intended Khz. Assuming not full range, in which case the phase changes look like a wheel going round and round.
You could of course step back in an auditorium and measure the phase angles of the sound vs the input, I suggest quick gating and MLS to even get a hint at what arrives, an it ain't pretty from a phase perspective.
You could of course purchase a RANE AC 22/23 2/3 way X/O with 24 db LW 4th order slopes and a phase/time delay circuit to allow you with a mic and phase readout to time align the X/O at your ears. Geez there's a novel approach.
To adjust for the delay in the accoustic centers of the drivers when combining horns and cone drivers.
In my opinion the group delay is a bigger issue. I did notice little comment on group delay. Look into the Joeseph audio drivers and X/O, 120+db/octave, phase coherent with minimal group delay, less that 0.1!!!
Just my input.
sean...While I very much agree with your opinion of Walsh drivers, and their phase coherency, I don't think that your statement "all sound eminates from a point source..." is correct. Even a small musical instrument like a violin radiates sound from most of its sound box area, which is larger than the typical loudspeaker cone. Since the original sound source is not phase-coherent, this cannot be an absolute requirement on the reproducing transducer.
That being said, I do confess that phase-coherent loudspeakers sound good to me, but I think that the reasons are not entirly understood.
Single drivers create comb filtering because the sound is being sent to your ears from different points on the cone creating many different path lengths. The cone does not move entirely together. The inner part closer to the motor vs the outer edge tied to the suspension creates problems. Also the very fact that the center of the cone will be deeper set than the outer edges is a problem unless the cone was absolutely flat which will create more unique problems. Oh well, just my 2 cents worth.
On further thought...here is one explanation of why phase coherency matters.
The original source of the sound may be larger than a point, but as the distance from the source to the listening location increases, the difference of distances between the listener and various parts of the radiating source gets smaller. The wavefront at the listener, for any reasonable source-to-listener distance is a hemisphere, and approaches a flat plane, where different points on the plane have very-nearly identical characteristics. For realism we want to reproduce this nearly-uniform planar wavefront.
One obvious way to do this is to use a planar speaker driven equally at every point of the diaphragm. Uniform drive at all points of the diaphragm is not easily achieved. (Quad electrostatics go one step further and drive the diaphragm variably so as to simulate the spreading feature of the hemispheric wavefront).
Although the original wavefront to be recorded is a large area plane the recording is made by a very small microphone that "samples" the plane wavefront at one point. It is the microphone, not the original sound source, that is a "point". Now, if the signal picked up by the microphone is rebroadcast from a point source transducer (speaker) the result observed at a moderate distance from the speaker will be a planar wavefront very similar to the original one that was sampled by the microphone.
Drivers in a truly time/phase correct design act as "one" driver(sound source)...hence the highly involving, musical presentation these types are known for...the drivers are in unison...sound the sound is very coherent and balanced...and the most overlooked aspect....very non-fatiguing...
Bigtee: You bring up some valid points for typical "full range single driver" systems. What you may have forgotten to take into account is how a Walsh driver works and is shaped.
Due to the shape and size of the cone, the section of cone that is closest to the motor is furthest away from the ear in terms of actual physical distance. Yet at the same time, it is closest to the ear in terms of a direct path when one is seated in a normal listening position. The lower section of the cone is larger, making it physically closer to the ear, yet it is further away due to the higher position of ones' ears at a seated listening position.
The end result is a relatively consistent wavefront in terms of arrival time vs frequency. That's why this is called a "bending wave" transducer. It takes into account the length, path and arrival times of the various frequencies being reproduced and where they are emanated from on the driver itself. Obviously, some attention needs to be paid in terms of speaker height vs seated listening height, but this is true of any speaker system.
As a side note, Ohm had to play with the shape of the driver quite a bit when redesigning the original Walsh driven Ohm A to come up with the Ohm F. If you look at pictures of them side by side, the shapes of the cones on the A and the F are quite different. Whereas the A looks like an upside-down funnel with a much broader flare near the base, the F uses the same basic "upside-down funnel" design but maintains a consistent rate of flare from top to bottom. If these were potentiometers, you could say that the Ohm A had an "audio taper" whereas the Ohm F had a "linear taper". Sean
PS... The Walsh's are FAR, FAR, FAR from perfect drivers, but they do some things VERY well.
PPS... Mburns: E-stat's and any other "panel" type speaker have their own set of problems. Each speaker design has its' own benefits and baggage. Plasma drivers are the "best" in terms of linearity, but they are just about the worst in terms of spl capacity when taking safety into account : )
At the urging of several parties, I decided to post a response on this over at Audio Asylum.
Green Mountain Audio
Hey Sean, I wasn't refering back to you or the Walsh speakers but attempting to point out that typical single driver speakers are no where near perfect. I'll try to be more specific. I did enjoy reading your explanation, however. I agree that the Walsh was a good attempt but, as you said, not perfect by a long shot. That brings me to my next point.
Are we buying speakers that are designed as accurate transducers or are we buying speakers that we perceive as sounding good to use as an individual? I have noted in the past that most of the popular electrostatics test so poorly in frequency response test that if they were box speakers, they wouldn't even be considered. I believe if you don't start off with a flat frequency response, then everything else is a moot point(from a accuracy point) We barely scratch the surface on this sight as to speaker design with its complexities. ( I have enjoyed Roy's contributions)
One of the reasons I believe in phase coherent speakers is there is no way a speaker can be accurate without having the phase relationships match those as recorded. I also believe in time alignment for the same reason. B&W did a test once using a phase corrected CD to time align their speakers. The panel they used prefered the time aligned presentation and perceived it as more natural(and accurate) However, B&W continues to make non phase aligned speakers.
This is a business for designers now. They have to convince people their idea is best. Advertising rules! But, what is it doing to our hobby and our striving for something that is more accurate. If accuracy is not the goal, then I'm throwing everything out and buying some Bose!
Bigtee, one of the reasons that electrostats measure poorly, is the conventional setups used for measuring them. Speakers are usually measured in the near field in a room or out of doors. Usually the former. Unfortunately, you are measuring a large radiating source in the near field with a point source mic. Respose varies over the large diapragm and, in the near field, you are only "seeing" a small portion of that diaphragm, hence response at only a fraction of the total radiating surface. Even out of doors you do not get to see the room contribution to a dipolar radiatior (not that all electrostats are dipoles). Measuring far field out of doors is also fraught with other problems such as ambient noise. Even anechoic measurement is a bad representation of the response as the contibution of the back wave is damped, unlike the response in any normal room.
The idea that electrostats function truly pistonically is incorrect, the large diapragms tend to "shivver" across their surface due to the uneven distributed driving force and the great mass storing quite a bit of energy. BTW I owned the Ohm Fs. And while they had some strengths, they rang like the bell that they are. Very fatigueing.
Viridian: I agree with your observations about the majority of stock F's "ringing like a bell". There are ways to DRASTICALLY improve their performance in this area though. Since "ringing" has to do with transient response and internal damping, any improvements made in these areas improve the performance in all other areas.
1) F's have a LOT of driver mass. Unless the cabinet is properly damped and tuned for the individual driver being used ( most from the factory are not even remotely close ), the driver will tend to overshoot on large peaks and ring once it is "thoroughly excited". By fine tuning / altering the damping within the cabinet, you effectively:
A) lower the Q of the system
B) reduce the impedance peak at resonance
C) reduce the rate of roll-off below resonance
D) improve the low frequency characteristics
E) improve the transient response of the driver as a whole
F) increase power transfer
G) improve the amplifier / speaker interface
2) F's are a very tough load. Besides producing a very low impedance at very low frequencies ( appr 1 ohm at DC and close to 2 ohms at low and mid-frequencies ), they are also VERY in-efficient. From what i've been able to calculate, i have one set that runs about 82-83 dB's @ 1 watt and the other set is somewhere around 80-81 dB's or so. The early Ohm A's were supposedly somewhere around 78 dB's or so !!! As such, you need an amp that is TRULY capable of a GREAT amount of voltage and current. On top of this, it must be capable of delivering that power into very low impedances at very low frequencies i.e. where you already need gobs of power to begin with. Many "big" and "well respected" amps aren't "quite as big" or "quite as respectable" as one might think when trying to drive this type of load.
3) Besides the low efficiency and low impedance situation, these speakers produce a great amount of reflected EMF. This is due to their very large motor structure. This makes them hard to control and load into as the amp literally has to "muscle" past the "back-pressure" that the speaker itself is generating. As such, all but the sturdiest of amps will cough up a lung when trying to drive these speakers. I can't think of an SS amp made "way back when" that could really make the F's sing. By the time that amps of this calibre started to show up, the F's were either out of production or in the last stages of production. Due to the low impedance situation and lack of bass damping, tubes are pretty much out of the question with this speaker. Even "professional" type amps like the big Mesa Baron don't work too good for too long. High current draw due to their low impedances tends to pull quite hard on the tubes, shortening their life span quite noticeably.
4) The factory wiring is attrocious to say the least. One needs to disconnect the factory wiring at the Walsh driver and bypass it altogether. Feeding signal from the amp via high quality ( low impedance ) speaker cables directly into the Walsh makes a world of difference. Not only does this change the amount of control that the amp has over the driver, high frequency response is drastically improved in terms of both quality and extension. The use of a "normal" speaker cable with its' higher impedance ( most speaker cables are at least 40+ ohms ) will somewhat reduce these benefits, but it will be a big step forward as compared to using the internal OEM wiring that was supplied within the F's. For best results, speaker cabling with a nominal impedance below 20 ohms ( at most ) works best.
With all of that in mind, i sincerely doubt that more than a few handfuls of people have ever really heard what a well set up pair of F's are capable of. Quite honestly, i don't know if the guys that actually built and designed these things way back when had ever really heard what these things are capable of under "optimum" condititions. If i did not have the test equipment that i have, know how to interpret the data that it presented to me and impliment the necessary changes that i thought that they needed and have amps that were up to the task, i myself would not have the high opinion of these drivers that i do.
Having said that, the two sets of F's that i have vary quite markedly in measurements and sonics from one another. While Viridian is probably aware of this, most others probably don't know that all Walsh drivers were made piece by piece using hand labor. Each driver is comprised of three different types of materials ( titanium, aluminum and paper ) and are divided up into individual sections along the length of the driver. Once these different materials were hand glued together to form one large cone, varying levels of foam damping material were applied to the driver inside the cone. This was done by means of adhesive to the back of the metal sections, which helped to damp the ringing that all undamped metals tend to display once excited. As such, variances from unit to unit were not abnormal due to all of the hand labor. This is especially true when they first started production and were refining the design and near the end of production. Given just the variances in performance between the two sets that i have ( even their frames are quite different ), i do not doubt that one person could have a set that works reasonably well whereas the next person has a set that was a disaster out of the factory.
Sorry to side-track this thread, but i thought that others that own or are interested in what is an "out of the ordinary" speaker system might find this interesting. I'll shut up now : ) Sean
sean...As one who always was impressed by the full-range Walsh driver (and as an engineer, I found the theory ingenious) I wish that someone with the knowledge and experience that you have would undertake to produce these drivers. The labor-intensive manufacture that you describe sounds like a good prospect for China. It appears that the full potential of the concept was never realized when they were in production. I bet you could sell quite a few of the bare drivers for $400 to $500, and let people build their own enclosures. No crossover network would be a big plus for a DIY project.
Sean, your knowledge is just amazing. I always learn so much from your posts. Keep it comin'. BTW, have you ever heard the Ohm As? I had the pleasure in NYC once and my impression, from casually listening, was that both strengths and faults were multiplied. A little bit of heaven with a little bit of hell.
Sean, your explantion may explain why, though I clearly remember hearing them, I have no recollection of what they sounded like. I probably just dismissed them. Of course as time went by, their unique solution to problems I was previously unaware of, piqued my interest. It was probably due to the problems of the time, that they inherently and by association (surrounding equipment) had, failed to attract my interest. I would love to hear what they are truly cpaable of.
El: I have contemplated just such a thing i.e. producing a newer, more refined version. If you read the Agon wanted ads, i have a listing for Ohm F's posted. While i could do some "tall experimenting" on the four that i have, i really don't want to destroy something that is fully functional, especially since they are "near and dear" to my heart : )
As such, i've been trying to find some drivers that are salvageable but in need of repair. This would give me a baseline to work from without having to start from scratch. Having said that, i may be better off starting from scratch, but that is SO much more work and harder to get started. I need to stop talking about such things and spending so much time on my puter and actually start doing them. Can anybody else relate to this ??? : )
PS... I do agree that a crossover-less design is a BIG advantage, not only to the DIY community, but to the overall sound produced. As to the costs of the driver, i have no idea what a finished product would cost. I think that Ohm was getting appr $1600 per driver near the end of production. Sounds crazy, but ....
Viridian: Thanks for the kind words. I do what i can, when i can. I like sharing knowledge / experience just as much as i do learning from others. As such, i try to throw things out in order to "feed the cycle" that keeps us all learning and growing. I do this in hopes that others will read what i have to say and contribute something that i don't know or haven't experienced. There are folks out there that make me feel VERY "dumb & dumber" in terms of their knowledge and levels of understanding. Those are the ones i love to talk to and learn from. Books and limited exposure to various hands on projects can only get you so far as there is SO much out there to learn and do. I am but an idiot trying to climb the ladder of knowledge : )
As to the Ohm A's, i've never heard a pair but know others that have. The "wanted" ad that i mentioned in response to El also lists "A's" too, but more for restoration than for "sperimentation" : )
Unsound: These speakers truly are capable of revealing what is upstream of them when "worked". In stock form, they typically have a VERY potent bottom end and rolled off highs. Obviously, the combo of those two tend to reinforce a specific sonic presentation / colouration. As such, any old reviews that you read about these will typically mention something about the bottom end "authority" that they displayed and rightly so. In stock form, they can shake a house. Even at relatively low listening levels.
My "better" set of F's can reproduce a 5 Hz signal at what most would consider a phenomenally high amplitude when compared to a lot of other bigger / fancier drivers ( including most "subs" ). In comparison, my HT mains that use two 12's per cabinet in a box that is 4+ cu ft in size, can't provide anywhere near the bottom end that my F's can. The F's just won't play anywhere near as loud through-out the majority of the remaining audio bandwidth though.
As far as top end goes, my initial testing showed these rolling off rapidly above appr 12.5 KHz when i first got them. They are now quite solid up to above 15 KHz with very usable output at 17.5 KHz. Due to the design of the driver though, the vertical dispersion at high frequencies is rather limited. This is not a big deal though as the "high frequency section" of the cone is almost perfectly situated at or very near ear level when seated. Standing up and walking around does alter the tonal balance, but due to the 360* radiation pattern, the sound remains very open and spacious even though there is a noticeable lack of extreme highs.
To further improve / alter the top end situation, i've purchased a pair of the original Infinity manufactured Walsh tweeters. This is a "mini" version of the full sized Walsh drivers found in the Ohm A's, F's and slightly smaller version of the G's, but it is markedly different in design and concept. They are literally a "free air" radiator as they have NO "frame" or outer suspension, making them VERY hard to package / transport. The pair that i have were damaged in transit, so i have to see what i can do to repair them. I'm sure that i'll learn a little bit about how to make these "tick" in better fashion once i dig into this project. One of my friends, who is an avid supporter / rebuilder of Plasma drivers, has offered to help me. I'm hoping that we can get these up and running again, but i'm not sure how close to stock they will be. Sean
Sean, 'ever consider of using the plasma drivers in conjunction with the Walsh drivers?
Plasma drivers! Ionovac, Hill Plasmatronics, Nelson Pass protos, are there others? You guys are the most esoteric audiophiles I have ever heard of. I thought that the dudes here in Portland, OR in the Triode Society building SE amps with archaic tubes as big as flourescent light bulbs to use with horn speakers as large as Yugos were out there.
Clearly, I ain't seen nothing yet.
Viridian...Say the word and we'll beam you up.
Unsound: My buddy is trying to get me into Plasma drivers, but the trade-offs are VERY steep when running this type of driver. Besides the limited output, there are health hazards and TONs of RFI to deal with when using them. If i were to mate a Plasma tweeter with the F's, i probably wouldn't like the F's anymore : ) Sean
Sean, I really don't know, but, it seems as though the plasmas are better suited for medium to high frequencies and the Walsh drivers for medium to low frequencies. If that assumtion is true, it might allow for flexabilty in the crossover region. Can the Plasmas be made to provide omni-directional output?
Plasma's are omnidirectional except when coupled with horns to raise their output. The problem with trying to mate the Plasma with most any other driver is that the Plasma is SO much faster that the sound being reproduced lacks continuity between the various drivers. Kind of like teaming a jack-rabbit with a turtle i.e. both are moving, just not in unison : ) Sean
Sean, I was led to believe that Walsh drivers bending motion was faster than the speed of sound. If that is true, would that still be too slow to mate with a plasma? With the advent of new digital mediums, that claim to go further up further in frequency output, the plasmas may be able to help the Walsh drivers deal with demands never expected or probably previously designed for.