Crossover questions

Thank you Sean! I will think about horns in a more thorough light. The cabinets of my father's speakers(horns with cone woofer), while excellent for their day, can be improved in several ways. Also, the quality of the passive parts(coils, caps, resistors, and wire) have improved quantum levels since those speakers were built. I will also take your advice about the "diffusors" to heart.

You are quite correct about the cost of BlackHole 5. I once made a few "sound boxes" at my previous company. We manufactured EL(electroluminescent lamps), for use in cell phones, pagers, night lights, etc. The whole technology is simply a capacitor that lights up when supplied with AC voltage. There was a lot of noise generated via the AC voltage(coming from the inverter)/lamp. My job was to get rid of it. I looked into anything I could. The sound boxes were just basically speaker cabinets we built(minus the speakers, but with a window to view an inserted SPL meter), which insulated the lamp/meter from the ambient noise of the plant. Got lots of wonderful experience with sound insulation materials. Things like acoustic foil, SoundCoat, foams of every sort, viscoelastics, rubbers, silicones, polymer formulations I developed(applied via screen or pad printing). In the end, the best solution was to simply screen print a third electrode(using my carbon resistor paste) which served as a "shield".

The experience of building those boxes and insulating them(with foams, SoundCoat, foils, BlackHole Pad, BlackHole 5, Swedak, etc.) was invaluable in teaching me about quieting down a box. Materials were free(either sample or out of the company's money), and I was being paid. BlackHole 5 proved to be an excellent product(I like the viscoelastic/multiple foams combination), and we did end up buying a bunch.

To be honest, I can(and probably should) build that BlackHole 5(or better) using viscoelastic sound panels(probably the same as the sheets you are getting from PartsExpress), and two kinds of foam(from Foamex or whoever) for a fraction of what Orca's retailers charge for it. Even incorporate some acoustical foil(very effective stuff) in the my homebrewed insulation.

Now I get to use all of that information! Speakerbuilding is an immense subject, and no one has all the angles covered, but it sure is fun to play this game. If you are going to be undertaking a similar project in the future, it would be great to bounce a lot of ideas off each other. Again, thanks for your help.

Sean by the way, I just came across a thread on Tweaker's Asylum from 'Clayton Oxendine' regarding a series crossover question(via web search on "series crossover"). So, I now have found at least one person in the world who has knowledge of this mostly forgotten technology. Again, thanks for your help in steering me toward this person!

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).