Update: 6-18-08. I finally put an honest-to-God finish on the Aethers. I also finally updated the cut sheet for the Tang Band version. We're good to go!
The Aethers are a hybrid dipole/vented "budget" speaker meant to compete with the likes of Martin Logan and other open-back electrostatics. The "live" soundstage is definitely the appeal of this kind of design, and it has a very different sound than the normal, boxed, monopole speakers we listen to every day. Surprisingly, these speakers pull it off very, very nicely, and with much simpler (and cheaper) components than you'd ever think possible. This project (or one like it) can be done less than $300 and requires no active crossovers or multi-amp setups. They are voiced for medium-to-large sized rooms, and will probably sound best in a room with carpet and/or window treatments.
AethersBOMXO.doc Here's a rundown of the parts list and crossover.
As stated earlier, the Aethers were my first original design. There is no way I would have known how to execute it, however, without the guidance of Andy G, who has nearly perfected open-mid speakers. Originally, these were supposed to be clones of his Blackwood speakers, personal favorites of his. These used a 3-way, first-order, linked series crossover. Unfortunately, my driver choices made this crossover unfeasible, so the project evolved and took on a character all its own.
There are three versions of the Aethers. They all use the same woofer (Dayton 8" DVC subwoofer) and tweeter (Seas 27 TDFC), as well as the same crossover topology. What changed between the versions was the choice of midrange drivers; this was because I originally did the project using discontinued drivers. Eventually, after enough people showed interest, I did a version of the Aethers using current, easily obtainable drivers (Version 3).
This version won the budget category at InDIYana 2008, and it's also the only one that uses currently available drivers. I'm very proud of this version, as it shows my evolution as a crossover designer. It uses the high-value Tang Band W5-704D midwoofer in the mids. These are around $25 each (a bit cheaper if you get all 4 at once), and a pretty good bargain for the price. One thing I have to say, however, is don't take Tang Band's FR measurements for face value. What you get in reality might not measure as pretty as that compressed "flat-looking" line they show you in the brochure. On the other hand, they have a really nice sound on their own. They extend pretty far, and have a mild bump out at 10K that brings out nice details of recordings (don't get paranoid, the bump is 20 dB down).
This version was a royal mess to put together for one major reason: Tang Band's measurements suck! It was a horrible, awful mistake to use their measurements to model this speaker. (Don't get me wrong, the Vifa and Peerless versions of the Aethers were done solely using manufacturer's specs and modeling software and sounded great). Tang Band's graph doesn't work at all like the real thing. But for some idiotic reason, I kept trying to make it work. I kept ending up with designs that sounded too "controlled" or "closed-in," which is totally not the point of this design.
Long story short, I learned how to measure. It still took many iterations (and slaps to the forehead) until things fell together. If you build this particular version, pay careful attention to the polarity of the drivers. Yes, everything is wired with positive polarity. This was a weighty decision, but with 1st order electrical filters, driver polarity is not a cut-and-dried issue. If you experiment with the polarity yourself, you're likely to hear the drastic change in soundstage as you switch things around. With all-positive, the soundstage is giant and lifelike--just like the other Aether versions.
Anyway, one more thing you might want to experiment with. As they stand, The Aethers have a few extra dB between 200-500 Hz. I did this because my ears liked it that way. If you think about it psychoacoustically, it makes a lot of sense, seeing as that is where the fundamental frequencies of the human voice and guitar (and most any other midrange instrument you can think of) lie. Hence, these frequencies also sound really good with dipole radiation. If this slight hump keeps you up at night, then you can increase the series resistor on the mids to 4 or 5 Ohms and this should flatten things out.
As one might guess, this design is a little tough on some amps. The impedance is mostly in check without problems, but the Dayton DVC sub does dip down to 3-point-something Ohms between 70-100 Hz. With a dedicated power amp, mono blocks, studio amp, or mid-fi receiver, you should be fine. If you have a budget reciever, you might want to check and make sure it can handle a 4 Ohm load.
I did this version because a few people on HTGuide and the PE board asked if it was possible. The mid drivers used here were the Peerless 830341. These were ridiculously cheap ($10), and had a beautiful-looking FR graph. The drivers themselves were not quite so beautiful... well, I take that back. The cones were nice-looking, and the build quality was excellent; it's just that pincushion frame that's hard to get over. Oh well.
This version has the same giant soundstage and vivid imaging as the Tang Band and Vifa versions, so if you build it, you're really not missing out. You may, however, want to put grilles on this speaker to hide those frames. Ugly pincushion frame aside, this is a fine Danish driver, and you shouldn't be ashamed of using it! It will deliver the Aether experience and you'll still have some money left over to buy a few dinners (or drivers, whichever is more important to you). Here's a picture to prove I built a second set of baffles to try this out, for the love of DIY.
This is the original version, the one that won the Budget category at Iowa 2007--and also my first speaker design from start to finish. The mids in this version are the Vifa P13WG-10-04. This is a poly cone driver, and out of all the mids used in the Aethers, it has the highest build quality. These were purchased as clearance items at Madisound for $20 each. They are still available at a few other dealers, but the regular retail price is not cheap: something around $43. The FR on these is amazing; just a perfect plateau. Unfortunately, the driver's natural rolloff was so precise that it was hard to fit into any sort of standard slopes using a 1st order crossover. So I fudged things as best I could, and in the end they sounded excellent--as Andy had proposed they would.
One thing that probably isn't an issue unless I point it out to you is that there is negative interference between the mids and the tweeter. This causes a bit of a FR droop between 5 and 10 KHz. Still, the original Aethers put out a very exciting and lively sound, and the midrange is wonderful! Vocals, snare drums, acoustic guitars, violas, and clarinets really sound like their real-life counterparts, which was my number one goal while voicing the crossover.
Here are the original Aethers singing on stage at Iowa 2007. Pay no attention to the fact that the tweeters are offset to the outside of the speakers. At home, I listen to them the other way around. However, at Iowa, just before they were to go on, the crossovers basically fell apart. With quite a bit of help from Pete S, I got things barely assembled and pushed them into place, not paying attention to which side I was pushing them.
And here are the Aethers duking it out against Dan Neubecker's beautiful and inventive Sound Rounds at InDIYana 2008. It was a tense moment in that room, I tell you. Everyone listened with bated breath: "Which would win, dipole or omni?" (I have to say I find this photo especially humiliating, pairing my sloppy woodworking next to Dan's exquisite craftsmanship. It's like a lean-to shack next to a Frank Lloyd Wright house.)
Okay, so these speakers are a bit unusually-shaped, so let me explain my thinking when I designed them. The MTM section is perpendicular to the floor because this will
cause the smallest amount of midrange "smear" as reflections bounce off
rear walls. The Woofer
section tilts out for two reasons: one, because it might help with center alignment on the drivers, and two, because it just makes for a slightly more interesting box.
also gave me the advice of extending the sides of the front panel about
4"--thus, making a "U-shaped" enclosure. If it weren't for this
U-frame design, the mids would have an unnatural rolloff, and would
probably require extra EQ circuitry. Also, it makes it look more like
a Martin Logan, and I am okay with that.
Note: This is a cut sheet for the Tang Band Version of the Aethers. If you are doing the Vifa or Peerless version version, you may want to move the midrange drivers in closer to the tweeter, if possible.
The bottom vented cabinet is very basic; its internal volume is 1.5 cubic
feet, it has some horizontal internal braces placed sporadically, and
the front baffle is actually 1.5" in thick (a piece of MDF in back and
a piece of 13-ply veneered plywood in front). It has a 2" vent that
is about 5.5" long, is moderately stuffed with polyfil and carpet
padding, which tunes the box to about 27 Hz. According to Unibox, this
gives an F3 of 26 Hz. I ran some sine waves through them, and the
model is correct. But with bass below 50 Hz, be ready to deal with
some room modes.
Also, if you're the type that sits around
and listens to sine waves, you will hear chuffing by about 30 Hz... but
not with normal music, only low frequency effects or test tones.
Honestly, there is nothing wrong with sealing this bass driver, and I
sometimes stuff a sock in the vents when I'm overwhelmed with bass.
This helps "tighten things up" a bit, and surprisingly, they lose very
little low end extension.
The Aethers are relatively easy to build floorstanding speakers. I was able to build them with just a battery-powered circular saw, a router, and a cordless drill. The pieces went together much more quickly than, say, the Cinderellas. These could be built using almost any jointing technique, from screw n' glue to biscuits to a nail gun. You can also get creative with the contrast between the front baffle and the side panels. In my case, I used 13-ply Birch plywood with a Maple veneer for the front baffle, and plain ol' MDF for the sides. It took me quite a while, but I finally did finish the Aethers (top photo on the page). The sides were done with Rust-Oleum brown hammered paint for a shiny, slightly sparkly finish. The plywood baffles I made a lot of effort to bring out the really pretty but subtle flaming in the maple veneer. I used several coats of sanding sealer, followed by several coats of laquer, then a protective layer of paste wax--all hand-rubbed. They don't look perfect, but they finally could pass for legitimate furniture.
Check out Jason's build of the Aethers! Wow!
Also, it looks like Jason's Aethers made a field trip to the RAW acoustics showroom. (Yes, that's a lot of speakers)
Good question. Up until I finally got the Tang Band version right, my opinion of them all differed. However, now I think it's a pretty simple matter of driver availability. The Vifa P13s are all but gone from the market, but if you come across a pair, by all means go for it. The Peerless, while still available are a killer deal at $10 apiece and are a hair more articulate than the Vifa, but will take some creative woodworking to dress them up a bit. Finally, the Tang Band W5-704D are a good fit for this type of Open Baffle design. Like the Peerless, they have a bit of extra detail, probably due to the hard plastic dustcap (just a guess). They were just a pain on my part because I put too much faith in the manufacturer's measurements, which were incredibly inaccurate.
So that's that. I've enjoyed the Aether journey a lot--and learned a lot as well. Now it's time for me to finish the last chapter and move onto other projects. Thanks to Andy G for his continued support and enthusiasm. To those who dare to build something a little different, I believe you'll find the Aethers to be a surprising and satisfying musical experience.
Starting at the low end, the bass is not dipole at all; it's just a simple vented box. Vented bass is a fairly common thing, and very effective once you tune the box right. Our ears are very used to it, even at live settings--about the only exception being classical music. Perhaps it isn't as true and accurate as an actual dipole woofer, radiating into free air, but it's a lot less of an engineering and mathematical nightmare, and it doesn't require nearly as expensive of a woofer. True dipole bass can have extremely low sensitivity and power handling capacity, as well.
Next up, we might consider the mids "dipoles," but they are not simply "open baffle" speakers. The 4" deep U-frame baffle on top makes this more of an "open mid" type of scenario. True open baffle speakers are tough, because frequencies want to wrap around the front of the cabinet ASAP and cause cancellation. The 4" sides lower the frequency where this cancellation starts to happen. I chose to cross the mids at 250 because it was about as low as I could get before dipole cancellation became an issue. Why so low? Most people don't realize it, but the fundamental frequencies of most midrange instruments are down in the low hundreds. Consider this: middle C is 261 Hz; the range of most male vocalists starts reaching the top of its range around middle C. How much of the voice do you want the woofer playing? Of course, much of the information in the human voice--or any instrument, for that matter--happens in overtones, which reach up into the thousands of Hertz, but still, you get the point.
Anyway, moving up to the mid-tweeter crossover point, I simply chose a point somewhere above 2000 Hz, because I wanted to get a good "3 octave spread" for the mids to work with. In fact, the more I could get from them without strain or "beaming," the better. Plus, since I was using a 1st order crossover on the tweeter, I wanted to push the point fairly high so as not to grunge out the tweeter with low frequencies. Also, the mids and tweeter are placed very close together, which helps make their transition more seamless--again, Andy G's recommendation.
From that point on, it was just a matter of voicing. And my main goal of these speakers was to have a very vivid, lifelike midrange. Thus, there is a hump of a few dB around centered around 400 Hz (as mentioned earlier). Try not to let this disturb you; try it, chances are you'll like it!
Ideally, I was hoping that an open-back speaker would take away the "boxy" sound of a normal speaker--that the sound in the room would seem to emanate from many more places and take on an ethereal quality. The spelling is in honor of a computer demo called "Aether" by the Finnish demo group MFX. If you don't know what the demoscene is, it's too hard for me to explain, so just go look it up or something.
If you have a fast enough computer with a good video card, you can download the executable and run it on your computer (Only as a very last resort, you can also watch the video of it on YouTube, but the experience is not nearly the same). It's stunning and mystifying and completely unique; and I only hope my speakers live up to the name.