Yes, Rulit does try to push envelop of something. He does exiting projects but I do not know how all of it manifests itself in actual results. I said that he  pushes the “envelop of something” as I do not know what this “something” is.  I never heard anything he does. 10 years back what I was traveling in Germany I was planning to visit him, we contacted him; preliminary agreed to meet but when I was there it slipped off my plans (cherchez la femme), so we never met and I never heard anything he does.

When I was talking about ultimate driver I did not really was looking for a brand and model but rather to create a retrial requirement for a hypothetic ultimate driver. Let me to copy what Rulit says as the eBay article will be gone soon:

“For sale are two Atelier Rullit RH-T903 field coil drivers. This pair is actually a result of my research on compression drivers. I have tried out every material I could think of, be it different species of aluminium or phenolic and cellophane for manufacturing diaphragms, but each turned out to be sounding somewhat uncouth, crude and aggressive, in other words PA (public address), and didn't have anything to do with home use. The up-to-date Rullit drivers are equipped with diaphragms from cellulose. They're playing bloody awesome - delicate and with a sensation of "just alike live". The chef's suggestion for music gourmets ... fits absolutely fine in two-way combinations like Klangfilm Eurodyn, Western Electric, etc. Résumé: Apart from rare exceptions, all PA drivers, including the ancient ones, have been developed for other purposes than subtle music reproduction and thus are hardly appropriate for home use. The cellulose diaphragms showed the way to another world, another dimension ...”

For sure the use of cellophane cone is a novelty but my primary concern in this thread is not what people do but what they are trying to accomplish. Among his objective Rulit named that he was searching ways to escape crude and aggressive sound from PA-minded compression drivers. For sure it is a noble task but there are plenty drivers that do not sound crude and aggressive but instead they sound soft and syrupy. So, based upon his description I do not know what he was trying to accomplish. Generally I do not like the “small” 802-size diaphragms like Rulit use. They are a bit too upper HF and do not do well at lower MF. The cellophane diaphragm might behave differently, I just do not know. Still, Rulit does have tendency for use wide bandwidth drivers with minimal amount of channels. This is not the direction that I like and Eurodyn or Western Electric would not help being brought as reference.

Anyhow, if use the Rullit’s input in ultimate compression driver subject then it would be “no crude and aggressive sound.” I am certainly on the same page with him.  However, all of the drivers that I ever seen and heard had the very same characteristics – if they did not sound aggressive then they were not able to show off aggressiveness when music does call aggressive and brutality.  This ability to show off the viciousness and violence if necessary is one of the many characteristics for which I like so much my Vitavox S2 driver. S2 is very much along with Rulit classification of PA drivers and S2 is crude and aggressive. However, if it used properly and sensibly then S2 is very much not aggressive, in fact it is as soft and malleable as baby kitten but if it was called upon to throw aggressive vigor then it has “it” with itself.   BTW, partially it is what my 6E5P amps do.

So, one of my requirement  for an ultimate compression driver would be NOT abolition of crudeness and aggressiveness but rather to ability of a driver to play soft and elastic when necessary and to play hard and bold when music is called upon it.

This is something I have been at for the last few years, I have tried a few drivers, at the moment some of my favorite are the vintage RCA MI 1443,  yes filed coil and some funny cone diaphragm,  they are used from 500 hz to 5 khz with a Fostex T500 tweeter on top, they do have the non crude or agressive sound, but most of all they sound very organic, they are able to resolve highly complicated music, but they do have that non agressive sound... when called for they cannot go and tear your ears apart or blow them away!  And there are times in the music this needs to be done.

My reference at the moment are the Beyma 755. I use them cut from 650 hz up to around 9khz, they can go really high but if you allow this then they start to get fuzzy,  I low pass them with a very small coil just enough to get the fuzziness out and let them do their best.  They are titanium diaphragms but with a plastic suspension (mylar). I have used and tried for some time a very few drivers that gave me what I wanted,  18sound 2060A with aluminum diphragm and plastic suspension, 18sound 1480 with titanium phrams and plastic suspension. Actually the 1480 and the Beyma 755 sound pretty alike. Now the 18sound 2060 and the 1480 are almost the same driver, 1.4 inch throat and 3 inch phram.  The main two differences are the phram material which in the 2060 (or 1460 with extension) is aluminum, the 1480 is titanium and Magnetic flux which is 1.9 tesla for the 2060 and 2.2 tesla for the 1480. 
So Mainly two very much the same drivers but one has higher magnetic flux and titanium vs aluminum diaphragms both with plastic suspension.
Soundwise both are very good drivers, but the 1480 is much better.  the most dramatic change between them is the weight of the instruments,  the 1480 has much more impact and the instruments seem to have more weight to them, they are more easily identifiable with better definition and separation between instruments.  This means that with complicated music, I can think right now of the Russian Easter Overture the 2060 plays it with no flaws, but the 1480 puts more shine on the trumpets and better weight on the instruments meaning also more separation and transparency, not very noticeable with simpler music, but when the crescendo gets here, you will want the 1480.  Now the beyma 755 has all the same attributes than the 1480, titanium diaphragm plastic suspension with 2.2 tesla, no wonder they sound very similar, as resolving and with the same weight on the instruments I have come to love,  but the tone of the Beyma is a little bit more organic, instruments are little more credible, you believe they are instruments a bit more than with the 1480,  and that is important.
18sound has since come out with a new diaphragm in the NSD1480 that is titanium nitride coated,  whatever that means it is supposed to have 6 times more stifness than normal titanium and twice as much a berylium, I call it the Viagra driver,  but I havent been able to get a pair for testing yet... and my urge to test drivers is decreasing.
Of course I started out with a pair of Altec 802 which were surpassed easily by Beyma 380 with plastic phram, I latter hated both. I tried JBL 375 bubblebacks and did not really care for them,  they were nice on piano, but wouldnt go high enough to make a credible violin and couldnt solve a good as the 2060.  I got Radian 950 which I thought at the moment would be a more modern version of the 375 with plastic suspension on the diaphragm and neo magnets, but I found that one shouty,  I went to a lot of trouble to tame it, and in the process getting some of it good attributes out of the way.  Bruce Edgar says there are drivers that work better on different horns,  I guess they didnt like round tactrix MDF horns.
I dont know if the case is the same for the TAD 2001 drivers. on my tactrix horns they just didnt sound right. I tried them in 2 different horns made for them, and the results were always the same.  They have very good soundstage,  I guess it was becasue I let them go almost up to 20khz, or whatever they could go up to, I didnt low pass them at the begining.  For simpler music you will have trouble finding a nicer driver,  female voices were very organic, foscused and with great soundstage (because the tweeter was disconnected)  They dont go all the way up, but high enough that you wont miss highs.  Of course the UHF is great to integrate music, I later added the Fostex t500 way up high. That being said there was always a whizzer sound present.  I know most people are not sensitive to say Lowther whizzers,  and they have a big popularity,  I lived and loved lowthers some years back, until one day something clicked in my head and I started listening to the whizzer sound, I didnt have the guts to cut it off, so I went back to my 802,  which killed lowthers down to 800hz.  I even asked a few friends if they could identify the whizzer sound and couldnt,  I envy them.  Now TAD 2001 exhibited the same sort of whizzer sound, but at a higher frequency, not very noticeable in the begining but with time it came to a point when I just could not bear it anymore.  Of course I could fight back with lower xover points and certain tricks, but the truth is , they are not very good drivers to beguin with, not resolving enough; I would put them next to the 2060, nice and sweet but when the crescendo comes on the Polovtsian Dances and the chorus goes in full force,  they shy out,  just cannot make what the Beyma 755 does with flying colors,  even distort on climax with 1.5 watts.
I turn my own horns out of sadwiched MDF and have made at least 10 different MF horns by now,  I try to match the driver with the exact horn size according to measurements and listening tests,  IME  horn loading makes a bigger impact than Xovers,  if you have a bigger horn and try to cut your drivers higher, they wont listen to the xover, they horn will control the cut off frequency most likely.
Right now I am playing with JBL2490 drivers and when a good low pass is added they can go real low,  I have them on 120 hz horns, have not measured them again lately but I can tell they are loosening up nicely.  I want to get some diaphragms for them with plastic suspension,  maybe that will help them go just a bit lower to blend in perfectly with my lower channel.
I am still looking to try the S2 drivers, which I heard on Romys old system and loved them, of course,  and GOTO 370,  just to see what the fuzz is all about...
At the moment I guess I can say plastic suspension is a very good thing, and high tesla, 2.2.

Jorge

Jorge wrote:

This is something I have been at for the last few years, I have tried a few drivers, at the moment some of my favorite are the vintage RCA MI 1443,  yes filed coil and some funny cone diaphragm,  they are used from 500 hz to 5 khz with a Fostex T500 tweeter on top, they do have the non crude or agressive sound, but most of all they sound very organic, they are able to resolve highly complicated music, but they do have that non agressive sound... when called for they cannot go and tear your ears apart or blow them away!  And there are times in the music this needs to be done.

Jorge wrote:

One more thing about the JBL 375, I did play around with them enough, I aligned the diaphragms several times untill they sounded their best and were very listenable,  This was some time ago now, I didnt turn my horns then, so I tried them on the original Hartfield horns with and without the "lenses".  which mainly obscured their sound.  I took them out of the Hartfield cabinet in order to have them sound in free space.  What impressed me about them was how low they would go, I once ran them with no Xover, carefully,  and they sounded very full.  I played with a lot of Xover points etc. until I got tired of them and sold the whole thing for a lot of cash.  It seems the diaphragms got missaligned on transit because the buyer said he was having some scratchy sound on one side, I instructed him how to realign the drivers a couple of times and never heard from him again,  I guess he was succesful. A close friend had the 2441 with the Edgar 350 horns and they sounded very good also,  but the sound wasnt as I remembered of the 375s...

Paul S wrote:

Jorge, not to stoop to a shopping list…

Romy the Cat wrote:

Here I would like to have a thread dedicated to a hypothetical ultimate MF compression driver. Use the existing, know to you compression drives as references.  Any thoughts?

Paul S wrote:

Here's something from a guy perhaps better known for his direct radiators: http://cgi.ebay.com/Atelier-Rullit-RH-T903-field-coil-drivers-/330581513356?pt=Vintage_Electronics_R2&hash=item4cf831948c Best regards, Paul

Romy the Cat wrote:

I will slowly upload, as time permits to write them, different posts on the subject of Ultimate MF Compression Driver.

The subject of bandwidth for Ultimate MF Compression Driver is complicated subject. If to look at the major questions for this subject then they will be the very simple: how low it shall go and how high shall it go. It does not sound complicated the answer is not so simple.

Let start from “how high shall it go”. There are a few schools of MF implementation by compression drives:

a)  MF driver gores to 6K, then another upper MF driver and then tweeter.
b)  MF driver goes to 10K-12K and then tweeter.
c)  MF driver goes to 6K and then tweeter.
d)  MF driver goes to 15K and then tweeter.
e)  MF driver goes all the way up and no additional tweeter used.

Let analyze the implementations.

The implementation A. There are very few companies that support this implementation. This setting requires superb driver’s time alignment, axes aliment and driver’s TTH characteristic match. This configuration is the best suites for multiamping. The major problem with this configuration is to dealing with lobbying of HF drivers but with vertical configuration it is doable. Ironically the only company that supports this configuration (Goto) does not believe in alignment, vertical configuration and their reputation in TTH filed is very questionable.  Anyhow, it is a legitimate configuration but I do not feel that this is Ultimate configuration for MF driver as it is two or more divers that cover MF. The biggest problem with it is the fact the very few people use this configuration and therefore there are very few or I would say none of the drivers made for this configuration, and whatever is made id not tested properly. No one will do a dedicated compression driver for one octave, like from 6kHz to 12kHz. What companies do is to designate very much the same driver to be upper or lower MF by using diaphragms with different Fs.  Some very few manufactures (like Goto) do make different drivers for upper and lower MF but since Goto users are mostly Morons and Goto themselves are very controversial I would not trust to what they do.

The implementation B. This configuration that I use and I find it more comfortable for Ultimate MF Compression Driver. From one side the driver does not go to high and do not deal with problem in implementation C. From another side the 12K is itself is self-sufficient listening range and an addition tweeter does not add sound but there the artifact of sound. It is very important as driving tweet up and down you do not change the amount of sound that tweet output as it happen in the configuration A but you rather change ONLY the amount to HF. If tweeter is closed very low, like 5-6K then you can’t adjust your HF and you MF separately.

The implementation C. This is the configuration that I do not like. The MF and Tweeter are locked and need to be balance according to MF and there is no way to dial in the HF. Some people go away by using very harsh tweeters in this configuration or the tweeter that have a small thump at 12-13K region. This give some help bit still I find it very flexible. Your room and your listening distance might have very different acoustic requirement at 6K and 12K and using a single driver that cover the whole upper MF and HF range is a bit problematic in my view.

The implementation D is not bad if our driver can handle it. The very minor problem that I see in compression drivers is hat in order the driver to be able comfortably and clearly to shoot all the way to 15K the drivers need to have small and very stiff diaphragms. Thos small- diaphragms most of the time demonstrate harmonic deficiency across MF and I more incline to use MF compression driver with fuller body.

The implementation E. In my estimation it never happened but it always right thing to do to switch your playback this configuration and to hear what your MF driver dose atop.

So, my own preference is to have MF with bass channels to run with playback and to have auditable a full range, fully balanced sound. Then add a tweeter but very surgically and very purposefully.   Mostly the configurations B feel friendlier to me. Still, I have to admit that if a person knows what he is doing and have right objectives then the very identical sonic results might be obtained by using any of the mentions configurations.

Now about the bass region – how low an Ultimate MF Compression Driver shell do? Some people would like to have a driver that goes down to 200Hz and some people use a driver from 1000-1500Hz and up. If the driver has bottom of 900Hz as many of them are then they mostly too cold sounding drivers. I think the ultimate range of MF compression driver still starts from 500Hz.It would be nicer to have a driver to go lower but an Ultimate MF Compression Driver would be use in Ultimate configuration that in my mind imply a dedicated lower MF channel the remove the LF stress from MF diaphragm. So, if the Ultimate MF Compression Driver is used from 1000-1500Hz then why shall it be able to play 500Hz? The answer is: he harmonic reserve – the driver that will be suited for 500Hz will have larger cone and softer sustention and consequentially it will play 3khz with more harmonic richness.

So my vote is for 500Hz- 12000/13000Hz driver. That is all that is bandwidth related…

Romy the Cat wrote:

Audiofilofine, I have no formed opinion about what Rulit does. I do not want to steer the subject of the thread to the wrong direction but can you share your view and your reasons why you feel that what Rulit does is a fantasy? Rgs, the Cat

audiofilofine wrote:

are only old obsolete  driver cocktail with homemade ingredients. no measure, no method, no philosophy...nothing , only diy fantasy

Yes, I do taste some slurp of “diy cult fantasy” in Rulit’s action, the romanticizing old drivers, creating the legion’s around the and so on. But it is the business nitch he is in and I know that he is associated in Russia with the people who are full time eBay saliva droppers – the guys who run Vintage Audio site. I very much hate those people from Retro Audio. Not to mention that for soviets is very typical to search a high spiritual meaning for the shiny crap that they dig out at Western junk-yards.

Still, the fact that he is associated with the primitive fools who run a chain of second hand shops and pawn shops in Russia does not necessary signify anything. Also, the fact that you are and I am not familiar with his measures, methods, or philosophy means that he has none of them.  The only familiarity I have about Rulit is by a few eBay actions that I seen from him. You have seen a lot of measures, methods or philosophy at eBay, have you? Sure, Rulit ride the hype and trying to brash up from it some business but it not necessarily mean that what he does is bad.

The point that I am trying to make is that there are predictable things and there are not predictable things. In my estimation what Rulit does comply with the things that have non predictable results. Knowing him personally and knowing his objectives it would be possible to predict the thing but I (and perhaps you) do not know him and with it would be necessary to actually experience what he does.

Sure, in some reading between the lines some expectation might be built but I have no need to built any expectations as I have absolutely no reference about what Rulit does. I have seen some Russian people went with Rulit implementation and report great results. Still all those people that did it where very much idiots and in my estimation their opinion on the subject was worthless.

So, as any beef you have with Rulit besides the fact that you are not familiar with Rulit measures, methods, and his philosophy?

Romy the Cat wrote:

audiofilofine wrote: are only old obsolete  driver cocktail with homemade ingredients. no measure, no method, no philosophy...nothing , only diy fantasy Yes, I do taste some slurp of “diy cult fantasy” in Rulit’s action, the romanticizing old drivers, creating the legion’s around the and so on. But it is the business nitch he is in and I know that he is associated in Russia with the people who are full time eBay saliva droppers – the guys who run Vintage Audio site. I very much hate those people from Retro Audio. Not to mention that for soviets is very typical to search a high spiritual meaning for the shiny crap that they dig out at Western junk-yards. Still, the fact that he is associated with the primitive fools who run a chain of second hand shops and pawn shops in Russia does not necessary signify anything. Also, the fact that you are and I am not familiar with his measures, methods, or philosophy means that he has none of them.  The only familiarity I have about Rulit is by a few eBay actions that I seen from him. You have seen a lot of measures, methods or philosophy at eBay, have you? Sure, Rulit ride the hype and trying to brash up from it some business but it not necessarily mean that what he does is bad. The point that I am trying to make is that there are predictable things and there are not predictable things. In my estimation what Rulit does comply with the things that have non predictable results. Knowing him personally and knowing his objectives it would be possible to predict the thing but I (and perhaps you) do not know him and with it would be necessary to actually experience what he does. Sure, in some reading between the lines some expectation might be built but I have no need to built any expectations as I have absolutely no reference about what Rulit does. I have seen some Russian people went with Rulit implementation and report great results. Still all those people that did it where very much idiots and in my estimation their opinion on the subject was worthless. So, as any beef you have with Rulit besides the fact that you are not familiar with Rulit measures, methods, and his philosophy? Rgs, Romy the Cat

Romy the Cat wrote:

Ok, let kill the subject of Oleg Rullit out of this thread. Rullit has very little to do with horn and consequentially with compression drivers. Sine this thread is about MF compression driver I think there is no reason to pay attention what Rullit does. Oleg does whatever is doible and sells whatever is saleable. He most likely has no interest or aptitude to evaluate compression drives.  If you look what playback he is involved then you will see only open baffles or very shallow horn that mostly work as open baffles. His drivers are basically full range drivers and it is very far from environment where compression drivers used. BTW, I do not take audiofilofine unhappiness with Rullit too serious. Any critiques without providing specific reasons or justifications are just shaking of air. The Cat

Romy the Cat wrote:

I will slowly upload, as time permits to write them, different posts on the subject of Ultimate MF Compression Driver.

I wrote a lot about colors at my site and people know that color discrimination of channels is very high in the list of my proprieties .  The color discrimination is a complex subject itself that encompasses the Absolute Tone and, color sensitively, continuing color, stability of colors and many other subjects. It is not my intention to elaborate on color topics in this thread. However, thinking about Ultimate MF compression driver I can’t avoid to think about colors and what is the most important – the color control.

First think first – I do not know where color comes from in compression drivers. Many  people make many claims that they do know but I did not see yet single compression driver that has deliberately proper amount of colors.  Many people think that more colors the  better, they are wrong as usually. Colors in compression driver is like salt on your steak. Without salt the meat might not feel cultivated, with too much salt the meat is destroyed. It has to be very right amount and it has to be very right amount of colors. With excessive amount of colors playback or a channel begin to demonstrate colorations of the satiation when specific colors become overwhelming force. Many audio Morons do not understand different between color power and colorations, I do.  I not only understand it but have ways in my own playback to enforce it.

Still, my way to enforce the deliberateness of colors (with use of Injection Channel) is superbly powerful and I do not even think to use have Macondo without Injection but it is not Ultimate way to have color control. In Macondo I use Vitavox S2 driver that is the most powerful color discriminator I have heard among compression drivers. Furtherer I drive it with very unique output tube that has a lot of own color attitude. Still it is not near enough to serve the colors in the way how I feel they have to be and the additional Injection is employed. The Ultimate way would be to have drivers, and the most prominent MF driver, with color control built in. I mean whatever in a driver is responsible for color need to be adjustable. I do not know what it would be but this is my requirement for Ultimate MF compression driver.

A reasonable question would be: if a manufacturer (if the manufacturer “get” the subject as most of them do not) could not make a compression driver with right amount of color force, then the color strength would not be need adjustment? It is good question. The color strength is dissipate-able force. The precise force of color setting would wary with listening distance, room acoustic, type of loading, amplification, the use of a given channel, the way how the neighboring channels interact with the given MF channel. The Ultimate MF compression driver is like puberty: the driver shall ability to be pregnant but to consummate the pregnancy is the business of the driver end user.

There is no know to me drivers with the adjustable color strength, no one even look in the direction. Still, if I am thinking about Ultimate MF compression driver then it must have control over own color output.