Hi Paul, If you feel large comp horn systems are worth exploring why not DIY a pair? Even DIY they are costly but not as bad as production. I know you are just as interested in field coils but I find no reason electrically or acoustically to use them though they are the flavor of the month. Where reasons why way back in the day audio moved to fixed mags. Happy listening
There are several reasons why your experience with the Cogent's differed from 2006 to 2007.
The system in 2006 was set up as a Cogent system by Cogent. The system in 2007 was owned and operated by Teres, and Chris Brady made his own crossover, which was completely different from the Cogent, and added a plasma tweeter, and pretty much completely changed the sound of the system. Another thing that is important to understand- when you heard the system in 2006 it had adequate power, being in a small room. In 2007 an impressive looking amp built by Chris Brady nonetheless produced only 3 watts output and the system was not multiamped. If you want to produce adequate SPL without going into distortion in a 2000 square foot ballrom, 3 watts is not going to cut it.
If you want to hear the kind of sound you heard in the room at RMAF in 2006, OMA is producing a four way system using the Cogent driver, as well as a version of the AC1 with a Cogent driver.
As far as DIY- you heard the Cogent system in 2007. I don't think I need add anything.
John (K), you know, it is not much short of a miracle that you live an hour from me and I have never bought a speaker from you, given that I've owned about 30 others in the last 4-5 years, and I talk to so many who have your speakers. But you wouldn't let me come over - something about no demo visits - I woulda bought something that day, probably. :)
I have to disagree with you a bit re: field coil technology. There may not be any 'good' (measurable) reason while they sound different (but I think there is, actually), but such is the case with much in audio. They sound different.
I have to say I like a man who tells it like it is (or as he sees it, at least) and also that what you say makes some sense.
FYI, my comments here (the thread) may have seemed rather out of the blue, but actually I was initially trying to respond to another (older) thread. After several tries, it just wouldn't 'take', so I started a new one.
And I am just posting out of curiosity: the Cogents and the Classic line with field coils are (or almost certainly are) beyond my reach. (As are the AC1s which I have not yet had the pleasure of hearing.)
It's just nice to know where the top of the heap is.
Well, Paul, you never know what is out of your reach until you ask....
There is a big thing (tempest in a tea cup) right now with people from LA to Germany and Japan taking Altec and JBL large and medium format vintage compression drivers and hot rodding them as field coils.
Several things are cogent (pun intended) to this driver transformation- the actual structure of the permanent magnet driver and whether it can properly be converted to a field coil motor given its pole piece and the room within the casework for an adequate FC motor. The other issue is the diaphragm design and compliance, phase plug, and how that sounds unto itself. In other words, if you never liked an Altec 288, no matter what diaphragm it had, do you really think you will like the field coil version?
These are issues I do not usually see addressed.
Many revered audio products were the result of DIY endeavors. Simple reasoning tells us this much. So I assessed my DIY potential vis a vis the sort of performance levels and product refinement I require and proceeded to shop for finished product. Each of us must make that determination for ourselves, however.
As for field coil drivers, I have no personal experience, but will speculate that they may well offer slightly better performance than the best of conventional drivers. In my case that didn't matter because I couldn't spend $15,000 for a pair of Cogents.
Given the vast price differential between field coils and the best conventional compression drivers, I had no choice but to choose conventional. They've worked out very well and only cost me $1000.
Paulfolbrecht, the Classic Audio Loudspeakers model T-1 with the field coil drivers is about $52,000 for the pair. The T-3 set up the same way is about $36,000 for the pair.
The reason field coils sound better is that they are like ESLs in the way that the field reacts to the energy in the voice coil. That is to say, it does not react (or sag) whereas permanent magnets of all types do (Alnico sags the least and so has the reputation for the best sound). The difference is quite audible.
Thanks for that insight, Ralph. I hadn't made the connection between the static field of an ESL and the electromagnet in a field coil, but it makes sense. And in my experience both types excel at low-level detail and nuance and liveliness, though of course the high-efficiency field coil drivers do macrodynamics better.
In permanant magnets, as you said alnico sags the least (has the least flux modulation under dynamic conditions), followed by neodymium and then ferrite - but shorting rings (Faraday rings) can help ferrite and neo motors more closely approach alnico.
Why do field coil drivers cost so much? Are they particularly hard to make? Or is the answer just the inverse effect of the economy of scale?
By "sag" I guess you mean a delay in response to signal. Is that correct? If so, I can see that as an issue with a driver that has some mass but I wonder how significant it can be on the wispy little diaphragm of a compression driver.
Macrojack, thanks for asking, as that's a very good question.
The "sag" mentioned by Ralph (Atma-Sphere) is a short-term reduction in magnetic field strength. As the magnetic field induced by the voice coil interacts with the permananet magnetic field, it modulates that field, so the permanent field strength is actually constantly varying a little bit whenever the speaker is playing. Because an electromagnet's magnetic field is instantaneously restored by the power supply, modulation of the field strength is negligible. One implication of this is that the quality of the power supply is a factor with a field coil motor, but fortunately high quality regulated power supplies are not terribly expensive.
Thanks, duke. So what I get from your answer is that there is lag (sag) at play in the permanent motor whereas the field coil can change direction more precisely.
How does that relate to my other question about diaphragm mass? And what about Metralla's question about cost? There is a enormous difference, it seems, between the price on conventional drivers and FCs.
Macrojack, to the best of my knowledge there is no direct link between moving mass and flux modulation (though there is a link between voice coil inductance and flux modulation). Now it well may be that higher moving mass makes the effects of flux modulation more audible, but I simply don't know whether or not that's the case.
Field coil speakers have always been more expensive to make. When permanent magnet speakers became available, the industry moved to them quite quickly due to the fact that they were cheaper.
Like a lot of things in audio (tubes to transistors, LP to digital), the move from field coil to permanent magnets was fueled more by cost motivation than performance. Field coils are a rising star these days in loudspeaker technology. Although more expensive, they are otherwise an easy way to get the speaker to sound more transparent.
Ralph - I have large horns and a 2 inch compression driver. Where should I look for a field coil driver that can replace my B&C DCX 50?
Macrojack, right now field coil drivers are custom affairs or at the least, pretty pricy. I know Classic Audio Loudspeakers modifies a certain JBL compression driver- seems to me by the time they are done there is very little left of the original driver.
Either way I would contact either CAL or Cogent- its likely that they are the major suppliers of compression drivers right now.
Such a large cash outlay for a small persevered benefit that I have not been able to hear or measure when I compared FC versions of dynamic drivers to alnico. Never tried FC comps. But with all things YMMV. I will stick to optimizing other aspects of front horn design for going FC for now. Still Cogent makes a cool horn loudspeaker I say more power to them. We need more horn loudspeaker designers on the bleeding edge. Maybe someday FC comps will be readily available and I will give them I try.
I have heard the Cogent field coil speakers a couple of times, lastly at The Show in Los Angeles circa 2006. It was a very small room and they were driven by Ron Welborne's new Terraplane 45 & 300B monoblocks.
As Paul mentioned, the sound was best described as "effortless" and "liquid". No matter how complex the material, the music just plain flowed with and ease I've never heard before. I'm not talking about a "soft" or traditionally warm tube sound. This was something entirely different. All the transparency and detail was there, staccato blasts from trumpet had the proper "blat" and bite, but there was glossiness or glare.
It's hard to describe except to say I have never heard any compression horn system present music in the same way as those field coils. They were incredible, both in performance and price.
I'd love to hear how far they've come since then.
My system performs according to your descriptions using the same conical horn that Cogent uses without the field coils. I have never heard Cogent drivers so I cannot say how close I am to what you heard, but it raises in my mind a question of how much is the horn and how much is the driver?
I meant to say that there was NO "glossiness" or "glare" in my above post.
Another memory popped up, I think Steve and Rich said they had to rush to finish the fabrication of [url=http://www.audiofederation.com/hifiing/2006/Cogent/1000/index.htm]the horns[/url] for THE Show in 2006 and just finished them a few nights before.
Macrojack, you've moved on to horns from the ZU's? Or in addition to?
I sold my Zu Presence last summer and bought a pair of horns from Bill Woods of Acoustic Horn Company figuring if they were good enough for Cogent they were good enough for me.
Bill also turned me on to B&C DCX 50 compression drivers which he says get pretty close to the performance of the Cogent FC drivers.
If you have the space, this option is worth consideration.
Steve & Rich of Cogent have spoken really highly of Bill Wood's horns at Acoustic Horn Company. A few years back, I asked where could I get the best performance for the money, within my budget, and that is exactly where they pointed me.
I really need to shoot Steve and email and check out how far they come with the Cogent setup since they are here in the Los Angeles area.
I'm under the impression that compression drivers (field coil or otherwise) vary less from best to worst than horns do.
According to Bill Woods and a few other sources I have encountered through reading, only a conical horn can deliver the original sound waves intact. Tractrix and elliptical designs cause cancellation within their bell which results in a distorted delivery. When you talk to Steve Schell, ask him about that.
After researching the various opinions I've heard, I'm pretty confident that Bill knows what he's talking about. Field coils likely will further sharpen what is already a phenomenally clear picture.
These horns may not be for everyone as they present a very focused and utterly unadulterated voice. I'm talking espresso black, straight whiskey, rifle barrel delivery. By comparison your cone drivers give you beer with milk in it.
Its weaker and murkier. I know you don't think so now and I imagine you will need a while to get used to good horns, but if you do, there will be no going back to the tame, diluted sound of big brand everyday, ho-hum, reviewer darlings.
I wish I could afford Bill's bass horns. Donations are welcome.
Thanks for this great discussion! I don't often find much of any interest to me in this forum, but now we're talking HORNS!
I apologize if I pull this discussion in a bit of a different direction from FC. I would like to hear more about the difference in sound from a conical vs. tratrix horn. It is difficult enough to audition most cone and dome speakers, but horns?!? We're talking damn near impossible.
Is there really that much difference in the distortions that lead to the "horn" sound between these two approaches? Also, I have heard that this can be corrected to some extent with a tweak to the crossover, like raising the pole. How much can be corrected in this fashion?
Hi Dan - Have you seen this?
Also the horn page:
After you've read this, call Bill Woods and ask your questions.
He's located up your way, incidentally. Hastings, Ontario.
Maybe you can go see him.
Thanks for the links, Macrojack. There is good information on horns. However, I still don't see anything that discusses the cone vs. tractrix sound. I'll do some googling.
Perhaps the answers I'm looking for will only come with hearing the difference between my current tractrix horns and some conical horns. The ante to play at that table is a bit stiff. :-)
Dan - Bill can answer your questions. 1-705-696-2092
I hunted around for info for some time before I found him and he answered my questions without a sales pitch and without dissing anyone else. He will tell you about shortcomings and compromises in all designs including his own. You'll enjoy the experience.
There is a discussion on the sound of conical horns vs. LeCleach, which is a kind of extreme version of the tractrix, so you might find it of interest, at the OMA Forum under General Speakers.
Thanks, Jonathan. I've probably read it but I'll do so again. I suppose OMA is even closer to me than Ontario, and I don't own a passport. ;-)
BTW, did you guys do any experimenting with different driver opening sizes? Like 1" vs. 2"?
I joined the forum. Any forum with at thread on Romy has to be great! :-) :-)