rdrysdale wrote:

So Jeffery, do you want one or two? Finally, just today I picked up a chuck that will allow me to easily finish some drivers. They are 9 inches in dia. and I've really been struggling with undersized tooling. You have to pay shipping.

rdrysdale wrote:

Our bass driver has a 12v field coil motor, it developes just over 20 kilogauss flux density using a low carbon steel pole piece. The exit diameter is 4 inches at the moment. The diaphragm is 6 inches in diameter and made of a single layer of carbon fiber with a 2 inch diameter voice coil using copper clad aluminum wire. The design of the driver is very different from most, the diaphragm is cone shaped and clamped rigidly to the center of the phasing plug, and the perimeter of the diaphragm is made of felt, and clamped with a mounting ring to hold it in place. The combination of rigid center mount and felt surround give a very well damped and precisely located diaphragm. Because the diaphragm is fastened to the phasing plug, it wouldn't be possible not to have the plug, however it would be possible to machine it in such a way that it would act as an exit throat and blend right into the horn. We haven't taken many measurements yet, and the final design is still being optimised. We are trying to find the best compression ratio by machining different exit configurations, and found some errors in calculations in our first design, which was very constricted. We redesigned the voice coil and the phasing plug and have made great improvements over the first drivers. We plan on the operating range to be from 40-50 hz up to 250-300hz. This driver is rather large, the phasing plug is 9 inches diameter, and the driver weighs about 40 lbs.

lately there was here and there some unhappy voices of the pissed audio-subscribers about the fact that some idiots-reviewers lately got tendency to writhe their reviews based upon the release notes of manufactures and without actually auditioning the components. I mean: a manufacture announces a new model, the reviewer read the specifications and 20 words description of this new product and then….  the “reviewer” go over the pages and pages of audio publications spreading his fantasies how wonderful his Patricia Barber’s double bass sounded in his listening room and how much he felt the Patricia’s attendance on his laps, I am not kidding: it is what they do lately.

Well, I would like to do the very much the same and to share some my own concerns that I got after I read your description.  Feel free to disregard them and an imagination of my madness.

1) With the targeting upper frequency of 250-300hz you have no need to make any phase plug at all. The phase plug is useful to optimize the delays at the throat arriving in the situations when the wavelength is comparable to the geometry of the pathways. In case of 300hz the phase plug is juts a waste of time/money that you spent to make it available. If you need some kind of surface to  “bounce pressure off” with intention to damp the cone then there are many other, less painful ways to do so, not to mention that your cone should not be damped but rather viagranized…. (it will be more about it below)

2) The highpass of 250-300hz make me to question it. There is not good compression drivers that would confidently and with reasonable quality  to do down to 250-300hz. So, are you planning to use your driver only in context of 6-chanle installations?

3) The bandwidth narrowness of your driver concerns me and makes me wonder if the midbass that your driver does is the correct one. Let me to explain. As far as I can see it, one of the greatest problems with any bass driver is the bass-driver’s ability to introduce the HF harmonic overtones within their bass. For instance many bass driver has different type of  “bad” rubber suspension. Their paper cones do OK but the rubber 9mostly very wrong rubber used) suck the HF is and then kills all high frequency’s overtones. As the result, the driver sound completely artificial. The introduction of a complimentary HF channel matching with this rubber-death bass driver do not assist the situation but juts mask it out.. The very similar is taking place in those curved horns. Let forget that in the bent horns each section acts as a individually-tuned resonant chamber and let to look only at the overtones killing. When sound travels across a curve of horn then higher frequencies attenuated more in the curve then LF (reflections). So, the LF harmonics and the fundamentals go through but the HF get killed in the horn’s curves. That is one of the reasons why all curved horns, with conditional exception of the “J-horns”, sound like a dehydrated camel who juts cross Sahara and who is covered with a think layer of shampoo (but without water) on his skin. Looking at all of this I usually feel that a properly sounding midbass driver must be able to handle at least one octave above it’s lowpass cut off.

4) Something suggests me that the carbon fiber cone is NOT something that you will use in this driver eventually and that that the carbon fiber is primary responsible party for the paragraph #3 and #2. I am sure that the VC is trembling in the gap like crazy trying to do wider range but the carbon fiber cone holds it up saying: “Oh, shut up, you shaky little bitch. I’m the carbon fiber - the material that used to suck vibrations out of tonearms, airplanes, and sports motors. I was designed with the specific objectives to increase the harmonic dampening characteristics and you, the miserable voice-coil, should not anticipate me to have any compile with your hysterical movements, even if you’re driven by the reference signal.”  Rich, I feel that by using the carbon fiber cone you severally compromise your driver and I think you eventually will look at the different direction. Perhaps it should be a different type of fiber/cellulose, perhaps it will be metal or some kind of plastic, or perhaps you should explore the opportunity to pre-marinade the cellulose cone (some people I know report promising results with chitin). However, when everything will be working properly I would anticipate that your driver would able to care in a straight horn up to 3K without plug or 4K with phase plug.

Now, I’m as well, feel the Patricia Barber right behind me….

rdrysdale wrote:

The bass driver will play to about 8 khz…

OK, this dose make some since, become I understood you that it droops after 300Hz.

I wonder what made you to select the 300Hz as a crossover point – the currently existing horn of the actual evaluation which driver sounds better at upper-upper bass? The reasons why I asked because of you said  “actually sounds quite good up to that frequency” (that I doubt as I feel that a good midrange driver should be more alive at upper midrange). Did you consider letting your bass horn to run way upper then 300Hz? I went over those experiments few years ago and I detect that 200-500 Hz are one of the most important frequencies where most of the fundamentals live and where is better do not have any driver’s ambiguity.  Also, there is another VERY important point. If you have your midrange driver to operate down to 300Hz then your midrange horn should have rate somewhere around 170Hz. This is a big ass horn and conspiring that you go for the fairly LF-heavy midrange the sucker should be really heavy. Contrary, pretend that you let the MF driver to run down to, I would say 500Hz. Now you can do away with a manageable 300Hz horn. The beautiful part is that that this smaller horn will be substantially shorter. As the result, the MF will output more HF (never hurt) and the most important the dissipation pattern will be WAY wider. You really might want listen 300, 500, and 800Hz produced by bass channel vs. MF channel and find out which sounds better. If you do find that the upperbass horn does better at HF then you defiantly need to match the MF horn to ~50%-70% off of the MF driver’s cut off. This is very important as if you have the MF horn too large than you loosing dissipation, loosing HF and gaining some boomy heaviness. If you have the MF horn too small then you have honk combine with aggressive and sharp sound….

rdrysdale wrote:

A bent horn does very much concern me, I think Jeffery is on the right track with a straight bass horn, maybe one could be built to exit into the room, and dive under the floor for most of it's length, but then there would be no adjustment for location.

A bent horn should not concern you: it should not be used. To go over all hassle you are going, to make own driver and to stick it into a bent horn is similar to us catching Osama Bin Laden and appoint him as president of United States. Oops, sorry - the bad example: if it happens then hardly anything will be changed in Washington….

rdrysdale wrote:

We didn't know what to expect from the carbon fiber, the original RCA drivers were made with phenolic resin and very thin silk cloth. We haven't been unable to get any suitable samples of phenolic resin to try, and since I have a patent using carbon fiber in the aerospace industry, we decided to give it a try. The very first diaphragms that we made actually sound better than the phenolic and produced slightly higher frequencies. The .carbon fiber is lighter than the phenolic, and is a little stiffer, plus there is no noticible ringing when the diaphragm is tapped. There may be other materials available that perform even better, and we will always look for these, but right now we are very happy with the carbon.

I do not know – I kind off agree with Jeffery: I should not label all carbon fibers the same. Perhaps there are some carbons out there that would not behave like …. Sorbothane. I personally hate carbon fiber in tonarms and this all that I experienced in Sound. Still if I did something like you do I would try some marinated paper, and yes, the marinated fabrics as the outer suspension.  Many good drivers with good tone use fabrics for externals suspension. We kind of never know what will work in there but to change the recipe of the marinate is always easier then to manufacture a new cone… I would be fun if you conclude that the best result you got if you soak a cellulose cone in 29-year-old Scotch…  :-)

Rich,

I think it’s too early to seriously to talk about sound of your driver. As I understand you have no horn for this thing. Your comment that the driver goes all the way unto 8kHz clearly indicates that you used wrong horn before. If you stick a driver into 4” throat of a promptly bult horn then… bye-bye the driver. The horn will completely overwrite the driver’s performance and the driver’s characteristics even if you go for a shortest tractrix profile. People mostly accustom to the Altec, JBL, Edgar and others toy-like upper-bass horn with oversized throat of almost triangular shape when the driver is acting as a direct radiator. In those so-called horns the horn largely inherent the sonic attributes of thier drivers … because in their “horns” the driver are responsible for sound not the horn loading is responsible for sound.

You, in your case went for very radical 4” throat with targeted 40Hz-50Hz of mouth. This is very drastic and your huge horn that will be required will wipeout what you know about the sound of your driver. When you put a first time RTA with the driver mounted to the horn then you will know what I mean….

Anyhow, I assure you that in 4” to 50Hz horn your driver will hardly be able to care 4kHz and what if does then it be very strange and very spooky decay, and that would be all right. Still, finding the correct value of filtering coil for this channel, find out how the voice coli of your midbass driver affect the MF driver, to find out how to tune the back chamber to the given horn, learn hot to deal with resonanses on the cone when the cone begin to feel the throat reactance of that all air in the bell of the horn….  and many other thing should take I would say a few month. It is if you have the horn already built…

Rich, when you bult the pair of those straight 4” to 50Hz horns (it looks like 10”) and make the rest of your system to work with it then give me a call and invite me in your place. Nope, not necessary to listen your playback! What I will be doing is opening a small kiosk next to your home and will be selling the tickets to the varicose Morons, demonstrating to them what Audio might lead to….. :-)

The Cat

This has been a very informative discussion folks. I am not a horn person... not through any lack of interest, but I am married. So, direct radiators rule.

However, I do not like the sound of speakers and so developed a process for turning cone and other styles of drivers into single pass transmission line emitters. Does not matter what frequency ranges you might choose.

This is only important in that I am offering to treat a test case for you guys, that may free up your choices in the critical fundamental range. And, Romy will be rearranging my posterior over a tweeter I recently sent him to test sometime this week or next. So we know we will have a report biased towards music making rather than specs.

If one of you has a driver that almost works, preferably a paper cone but any type will work, I am offering to provide a small experiment that just might relieve some problems. Think about supplying your horn throat with a phase and time coherent flat wave. One that, like Soliton waves, holds on to it's energy coherence regardless of what it encounters..... anyone interested? It will be free for a few of you....
Bud

Jeffrey Jackson wrote:

I feel that the first decision when designing a horn speaker is to decide how many horns and the corresponding crossover points.. then pray that suitable drivers exist.. if not, then make them...

I’m religiously against this approach. Most of the bad thongs people do with drivers, crossovers and channels utilization is because exactly this vision. To intellectualize the crossover points, to project a desired amount of channels and then search for the driver is VERY absurd way to go.  Everything starts from an observation of performance of a specific driver when you recognize what the driver needs and detect at which frequencies and under witch loading the driver does what you need, then, only then (!) the ideas how this driver might be used (including it’s conjunction with others channels). There is NO other ways to go!

Jeffrey Jackson wrote:

Personally, I think that 3-way is possible…

I do not. Horns produce very different and kind of “dry” upper midrange.  There is a secret how to use that upper midrange. I learned over my experiments and auditioning many different horns that in order to soften out this upper midrange and balance it subjectively a horn installation MUST have LF section that goes all the way down to sub 25-30Hz. The LF needed not for sake of sound but for the sake of “compiling” the “strange” radiation patterns, to hydrate the horn’s upper midrange and for few other things. Many folks use horns upper midrange within their systems that can handle properly no lower then 40-50Hz and consequentially they end up with typical “bad horn sound”…. So, no horn channel can do 20Hz, unless you live in angar for Boeing 727.  In addition I have Real Estate like this then not exactly believe conceptually into the lower bass horns. Therefore, I do not feel that a properly performing 3-way system is possible. When a channel take care about 20-30Hz then the demands for those drivers, those enclosures and the entire ways of LF producing is totally different then with other channels, so it would still require as dedicated channel. Yes, the 3-way is possible…. with a complimentary extra LF channel. Certainly it feasible to get good sound with 3 channels but, come on! If I am being a snob then I should be a compulsive snob and go all the way down….

rdrysdale wrote:

When we crossover down to 200hz everything starts sounding terrible, just starts sounding right at a little over 250hz. We never crossed over above 300, we need to do this.

And when you cross your driver it at 600Hz the MF will sound way even better then it sounds now.

rdrysdale wrote:

I need a fast way to prototype horns, since I can't go down to K-Mart and get one.

You might try what I did: make them form paper. Regular thick paper, in my part I got a large roll from a client of mine that “went to dark” and I made many horn form that paper. You should not make good horns to try but the “10-minutes horns”. They all will be conical and they all will have huge paper coloration, not to mention the huge throat distortions. After listing a few of them you will be able to tune- off you listening consciousness from those coloration and listen ONLY what you intend to listen. I still have in my storage some experimental horns of mine; the paper horns coated with rubber glue and spread with lead shots while the glue was fresh… Certainly the paper horns are very rough approximation but they is juts prototypes… it is nice to change the horn cut-off by re-applying Scotch in a new location…

Romy the Cat wrote:

…. The “live” bass never “dynamic” and ... Rgs, Romy the Cat

slowmotion wrote:

I don't understand what you mean here, Romy? To me "live" bass ( like when listening to an orchestra ) is much more dynamic than any reproduced bass I've ever heard. Also if listening to a real contrabass in a normal listening room the real thing is way more "dynamic" to my ears...

Anyhow I was thinking about it a lot a few years back and this is what I concluded. When we talk about "bass dynamic" we do not imply bass’ dynamic range. We do not really feel bass’ dynamic range. We can instantly identify a compression of dynamic range at higher frequencies but with bass it works differently. The Bass’s octave very short and bass usually is not evenly reproduced within octaves. Furthermore the mechanisms of bass reproduction, being imbedded into listening space, introduce very high contamination of bass by own residues of reproduction efforts. As the result, the dynamic envelop of bass at very high degree overwritten but the methods or reproduction (it will be more on some other aspects lower).

When we register reproduced bass we unwillingly loosing out humane reference to "dynamic” (as dynamic range) of bass notes and instead we recognize the "dynamic” as a motion of bass in space. Interestingly that as soon we recognize the “dynamic” of bass as a movable, variable and changeable force than the “dynamic” characteristics (attack/decay) of playback systems become prominent (actually they are always prominent but with bass it juts even more dominating). The attack/decay parent of bass has MUSH more affect on us then the absolute dynamic range of the bass’ octaves. Still, when we recognize the “absolute dynamic range” we presume the deviation of signal over the noise floor. Well, the nose floor in bass region is quite complicated thing and it is not accident that I used the phrase: “the attack/decay of ENTIRE playback system”

Bass to be properly reproduces should be enveloped into a certain acoustic environment, the certain reverberation time or what called the “decay time” (usesly we use –60dB and look how long it might be in seconds). The shorter reverberation time the sharper and “faster” bass sounds (in addition the effect of phase randomanization within the diminutive RT60 has not space/time to kick-in). But here is the catch: we do not want this “sharp bass” to exists because it sound like claps. So, the wily engineers UNINTENTIONALLY implement into this speakers and amplifiers the mechanisms that would produces “better bass” in the environments were bass should be naturally “too sort” and “too fast”.  So, while we false-fertilize bass with overwhelming amount of the lowest (usually second) harmonics, twist attack/decays of our amplifiers and do some crazy “tricks” with amplifiers/speakers interfaces we overwrite bass unrecognizably and present to ourselves juts dead overly possessed bass. To look at this “dead bass” and try to estimate it’s “absolute dynamic” is similar to looking at fish broth and trying to assess if it was an ocean or a river fish.

So, what we feel, when we are talking about "live" bass being more dynamic, is the fact was not bass but the Symphony Hall with it’s 40Hz decay at 60dB within 3-4 seconds. Also it was the sound where there are no thermodynamic distortions by poor electronics, no flux modulations of magnetic, no mechanical genericism of speakers’ suspensions and no many others “seriousness eliminating contributors”.

Looking at all of this, when I try to reproduce bass I at trying to imitate not the bass itself but the attack/decay patters of the listening environment and therefore most of the reproduced bass that I have hear for audio it “too fast” for me. This “too fast” and “too dynamic” might be OK for any music but as soon we hit classical music then the “fast” bass act like a knife among the ribs.  The bass should not be fast or slow: a reproduces listening space should sound like the “life” listening space and the bass in this space should be whatever it is. It is VERY- VERY- VERY complicated to replica the real dynamic range of bass AND at the SAME time to maintain the reproduces listening space’s attack/decay patters AND at the SAME time to use the LF channels to control the reverberation times within the reproduced space (you would need two LF transducers: one to care the signal and another to counterfeit the decay signature of the “optimum” for given octave listening space)

In the end the wrong attack/decay patters is MUCH more DEVASTATE MUSIC then a compressed dynamic range and this is why I always say that “live” bass never “dynamic”. The “live” bass rather has long decay and (BECAUSE OF THIS) it feels like it has high dynamic range. I do not think that this is imposable in playback.

PS: That all is not a secret and in way it is all commonly known things. The only regretful part that I feel that since I posted it I will see in a few months some kind another idiot-reviewer will brainlessly snatch the entire notion and will shove to the poor audiophiles some kind of new farts-producing machines. It has happened a few times before in audio publications. I remember in past, when I made some serious posts at AA, I had a tradition to intentionally implant in the concepts some strategically placed errors and I was very gratified when I have seen that the idiot-reviewers swallowed and copied the whole peace without even remote understanding what the hell they read. Few time those cretins even use my “off the wall” semantic. What was even more disgusting (it happened twice) that before the industry assholes decided to convert my serious posts into this marketing BS they made the dirt that runs the AA to delete my posts form AA archives.