Trelja, e-mail me and we can discuss speaker design sometime, if you like.
My opinion is that series crossovers aren't a "forgotten technology", it's just that they are difficult to design, and are very unpredictable (very difficult to model with computer programs). I believe Joseph Audio's legendary x-overs are series, and his are supposed to be the steepest in the industry. The Stereophile review measurements confirm it, too. You can bet he hasn't "forgotten the technology".
I have two suggestions for you to check out:
First, if you like connecting speakers directly with no crossover, consider building a system with Fostex full-range drivers from Madisound (similar to Lowther, but much cheaper). At least visit their site and take a look at the drivers, and their flat frequency response. I've never heard them myself, but I bet they're worth the money, wheras the Lowthers are insanely expensive!!
Or second: Consider the Bottlehead.com speaker kit. They connect a bunch of aluminum coned midwoofers in series-parallel, use a high sensitivity tweeter (looks like a Focal clone), and the sensitivity is around 95 dB. It's an easy load to drive.
If I didn't already have several speaker projects going, I'd have bought the Bottlehead one immediately. I'm actually trying a project of parallel midwoofers. it will be a more difficult load to drive, but with these particular ones, it might work. I hope to use two tweeters in parallel per channel, and the sensitivity should be around 96 1w/1m. The catch is that the cabinet will be quasi-dipolar, and I'll augment with whatever powered subwoofers I have on hand...currently the Sunfire.
I just bought some Infinity Emit ribbon tweeters from Speakercity.com for only 40 bucks a piece, and they're simply incredible! I bet they're 99% of the performance of the Raven R-1's, at least until you get closer to their thermal limit. |
Noquarter, thanks for your input. Last night I visited a great website(sorry that I don't remember it now) that dealt with series crossovers in a very strong manner. Featured prominently were John Risch, Clayton Oxendine, Bud Fried, and others. Lots of good information. Including things like zeta(the important thing in series crossovers) calculators, and some real world projects. I am sure that some of the information I will relay here will be incorrect; it was a tremendous amount of stuff to drink in in a very short time.
Zeta is one of the determinants in how quickly the crossover rolls off the driver(???, I kind of forget now). It seems that a zeta should range between 0.7 and 1.2+. At 1.0, it is more analogous to a parallel network. A zeta of 0.7 is said to make the speaker much more upfront in sound(a good rocker's speaker), while 1.2 is more laid back(more like an audiophile speaker - "Boston Bland?").
A two way, 1st order series crossover is very simple to build. In fact, it uses the same values for the cap and coil as the 1st order parallel network. Obviously, how they are connected is different. I do wonder what a series crossover in my speaker buys me. Running the mids flat out would obviously save me the cost of the coils. I am not sure if the sound would be improved over running it with nothing in the circuit. I am also not sure the sound would be detrimentally affected by the wiring of a cap on the positive leg of the tweeter's circuit(ala a parallel topology), as compared to the way driver's are connected in the series crossover configuration.
Wiring in multiple midrange drivers is something that the author has described(in several examples), so he has that question of mine covered. One of their rules is to use drivers that feature a very broad operating range. I did a little thinking of the midrange, and my desire is for one that is very efficient. The Focal Audiom 7K comes to mind. About 97 dB sensitive, with an 8 ohm impedence. I remember it being pretty flat from 100 to 10000 Hz. Drawbacks are the lack of bass response, and extremely high cost of this driver. I believe they also manufacture a driver that gives up 1 dB of sensitivity at about a 40% cost savings. I really like Focal mids and woofers; finding them punchy, dynamic, and clean.
Another critical factor in the series crossover are the coils. It is important to get as low a DCR as you can afford. AlphaCore Goertz were recommended over Solen and North Creek. If I remember correctly, the rate of rolloff is also related to the DCR.
I will look into the Infinity tweeters at the website you listed. My concern with them is their sensitivity. Do you know that offhand? I presume it would be much lower than that of the Raven. Not that I have decided to use the Raven, but it is on my short list. |
I doubt it's much lower. To my ears, it's about 93 dB, wheras the R-1 is supposed to be 95. Speakercity also have the Hi-Vi Research RT-2 Ribbons close-out priced for only $31 a piece...I bought a pair of those too. They aren't flat though, and will need a gradual rolloff below 10kHz to bring the top octave up. By contrast, the Infinity Emit seems to have nearly the same dispersion as a one inch dome, and even more surface area. A pair of the Infinitys in parallel might be a better approach than a single R-1, at least where money is concerned (i.e., more surface area and higher efficiency). To my ears, it's as good as the circular ribbon Genesis uses, and that's saying a lot!
If you're wanting several midwoofers in series-parallel, then of course your cost will go WAY up. I still would like to suggest the Bottlehead kit. You could even modify it by using a different tweeter, like a Focal dome (or that pricey new one Kharma uses), a Raven, a Fostex, an Eton, or whatever. As is, though, I bet it would more than suit your needs.
If you have more money than sense, you might want to buy a pair of the new Accuton DIAMOND DOME tweeters, for $2500 a piece!! I bet they are just killer! Supposed to be pistonic to 100 kHz!!
Actually, the 8 AWG North Creek air coils have the absolute lowest DCR of any inductor on Earth, and DCR is always a direct function of the cross sectional area of any conductor. The main advantage that Solo's or Alpha Core's foil-coils have, is in reduced skin effect, since the entire conductor is a ribbon, so it conducts electricity entirely on its "skin". However, their largest ones are only 12 AWG, so their DCR is radically higher than that of North Creek's 10 or 8 AWG air core coils. Solen even makes 10 and 12 AWG heptalizt coils that are supposed to be magnificent.
In one of my projects, I went from a 14 AWG Solo CFAC inductor (identical to, and predating, Alpha Core), to a 10 AWG North Creek, and every aspect of performance improved (that driver is a Dynaudio 15W75-04). |
Lots of good dialogue here Noquarter. Thank you. If you are interested in seeing an interesting site on this series crossover "thing", please go to
http://home.iprimus.com.au/gradds/index.htm
It may just keep you busy for a while.
You are correct in what you say about the North Creek coils. It is just obvious that their 8 or 10 gauge coils would have a lower DCR than AlphaCore Goertz, whose largest are 12 gauge for copper, 14 gauge for silver. Don't know why I went along with their statement. It should be more than apparent. Perhaps they offered this up before these North Creek coils were introduced. Not sure when that was, but the last time I bought North Creek coils(1996) their largest wire gauge was 12. I am not a fan of the Solen heptalitz coils, I find North Creek much better sounding. And the Goertz would give a sound of another color, whether it is preferred is a matter of personal taste. I will need to check out North Creek to see how expensive these larger gauge coils are. Again, by running the mids flat out, I can save that expense.
I know that I prefer the sound of the mids without a coil in the circuit. Presuming that the driver is of the requisite quality and robustness, it is a no lose proposition. I would like to hear an argument as to what a series network could offer over having nothing in the path of the midrange.
I would not install more than two midranges in each speaker. As you pointed out, the cost of going crazy in this area adds up fast. I am leaning towards the two midranges, despite my liking the time alignment(one midrange) my Coincident speakers feature. Their sound has more than sold me on the arrangement.
Accuton drivers are not new. I first came across them in the early 1990's. While I didn't spend a lot of time with them, I can describe the sound as very smooth and natural. While pricey, they are not as expensive as Raven. I would not use Accuton drivers in this project because they are lower in sensitivity(usually 88 - 90 dB/2.83 V), and are not physically robust. I used to work with alumina(electronic substrates, paste, and I also used to tape cast it), and while very hard, it is very brittle. I have seen these drivers shatter rather easily in a speaker that was involved in a move.
In researching the EMIT-B ribbons you recommended from Speakercity.com, I found the sensitivity was too low for this project @ 90 dB/2.83 V. Price is good at $40. What do you think of the sound? I have not been around an EMIT driver since 1988.
The Ravens are available in sensitivities of 96 and 98 dB/2.83 V. Very high, but they are very expensive. Not sure if I want to put this kind of money in a speaker when I will be doing the cabinet work myself. While I have no problem with the construction of the box, I have never done any finishing. If I am going to build an expensive speaker, I kind of think it deserves the "living room" look.
I will also look into Cabasse drivers. I once helped a friend in a D'Appolito project using these drivers. They feature some highly sensitive drivers in their line. Sound is fast, and clear. Maybe not as laid back as I might want. We'll see. Following along Sean's recommendation, they offer some horns, which I should investigate. 108 - 110 dB/2.83 V sensitivity. Interesting.
Needless to say, the diamond domes are out of the question. Maybe Liz Taylor would be interested...
I will check out Bottlehead.com today. Thanks for steering me to their site.
My only listening of Fostex drivers were in a speaker that had no grunt to me. Kind of shallow. Lively and able to play loud, just that I prefer a little more "blood and guts" to the sound. Maybe I am selling them short. Have you heard them in a better light?
I am on record at Audiogon of not being the biggest fan of Focal tweeters. They can play loud and clean, just hard on my ears. But, I have really been impressed by the sound of Osborn speakers, which use all Focal drivers. When driven by more sedate electronics, such as Electrocompaniet, I have to admit the sound is first rate. Their mids and woofers are right up my alley, however. Available in high sensitivity or high impedence versions. So, that is why I will probably go with them or Cabasse.
Again, this is a wonderful dialogue. Something about the speakerbuilding hobby that I can never get tired of. Thank you! |
Well, good luck in your project. I'll check out that iprimus site.
I never said Accuton was new; I said the Diamond dome was new. It will be interesting to see which manufacturer uses it first.
The sensitivity for the Emit-B seems higher than 90dB to me. The sound is fantastic imo; far more detailed and dynamic than I was expecting. It's a modern unit, with Neodymium magnets, so it's bound to ouperform those Infinity units you heard in the 80's.
Also, the published sensitvity for the new Raven R-1 is only 95 dB, the higher sensitivity is for the previous models (now discontinued). I think a pair of the Emit-B's in parallel would equal or exceed that sensitivity. Keep in mind that neither of these small tweeters will work below 3kHz.
As I've said before, if you absolutely want to run a midrange driver "flat out" you should consider a fullrange speaker like a Lowther or a Fostex. I've not heard the Fostex drivers, but their specs look more than adequate for their price, even a match for the Lowthers. The 8 inch model has nearly 100 dB sensitivity!! A series crossover isn't quite the same thing as running a fullrange driver with no crossover at all, imo.
Have you looked at Madisound's site, under Fostex drivers? Also, their ribbon tweeter looks about as good as the Raven R-1, and the Fostex one is only around $100...half the price.
I had thought that your goal was to throw something together for your secondary system, and to experiment; I didn't realize you wanted it to be a "statement" project. Those can be difficult and time-consuming...and let's face it, neither of us is a world class designer.
I, too, am no fan of Focal tweeters. Problem is, if you want to use only one tweeter, and decide you'd rather have a dome than a ribbon, the Focals are the only ones with high sensitivity, without horn loading.
The problem with using compression drivers and horns, is that you wind up padding them way down to match the lesser sensitivity of the midwoofers, so a lot of power gets wasted in the crossover, and I'm not sure it's even possible/ideal to use series crossovers in such an application.
I think you'll find, that unless your living room exceeds perhaps 7000 cubic feet, you won't need a speaker higher than 100 dB sensitivity (even with only a 3 watt amp)...and in any case, without the proper room treatment and placement, you'll hear more of the room's echo than you realize, imo. |
