ATTENTION: The Audax AP170 and Vifa D25ASG are No Longer Available.
This project is displayed for reference and archival purposes.
(Pronounced "VO-gan" or "VAY-gan," depending on where you live)
They say the best design for a neophyte speaker designer is a 2-way. Of course, it seems that few of us actually follow that advised path. I was no different; my first original design was a 3-way with dipole mids. It was like I had made it through high school algebra but never actually graduated the fifth grade. Obviously, I knew my time would come, and I'd have to find out once and for all if I could actually design a basic 2-way system, or if the Aethers were just some sort of fluke.
Well let me tell you: while a 2-way might seem easier (hey, it's got one less filter to worry about), doing it well is no easy feat. But in the end, I'm very satisfied with how this project turned out.
This project's impetus was that I wanted to build a set of bookshelf speakers for my father in law. I wanted to build him something that had some sort of excitement to it, either visually or audibly, so he could understand, first-hand, why DIY has real advantages over retail speakers. I debated building him one of several proven projects by other designers, but nothing quite grabbed me. Meanwhile, I was starting to accumulate a few spare drivers that I had no idea what use they would go to. I decided to sketch up a cabinet and go ahead and try doing things myself.
Quick BOM and XO: Vaagens.doc
I bought a pair of these woofers from Parts Express when they were being sold ridiculously cheap as the Deal of the Day. I had no idea what I'd use them for, but I happened to be making another purchase that day, and for the price, I just could not turn them down. Physically examining them, you wouldn't expect much; they have a plastic frame and a small magnet. But the Frequency Response looked like it would be very easy to work with, and the T/S parameters showed that they could get some decent bass in a vented box.
I still consider myself a newbie in the DIY speaker world, so it should be no surprise that I the first time I heard a Vifa D25AG tweeter was actually at Iowa DIY 2007. The tweeter design is 15 years old--and looks it; very early 90's. But despite its dated looks, I pretty much instantly fell in love with the sound. They had excellent dispersion and were very smooth and easy to listen to. Sometimes metal domes get a reputation for being harsh-sounding, but I found these to be anything but. A few months later, someone on the PE board was selling a pair for very cheap, and I jumped at the chance to use the tweeters. What I didn't realize until later was that these weren't the normal D25AG, but rather the shielded version, which had a much higher Fs.
Originally, this was just going to be a rectangular box of about 16 liters, but when I sketched it up it just looked so boring I could hardly stand it. I knew I could do a trapezoidal cabinet without much trouble, so I sketched that up of the same 16 L volume... much better! I also decided to put the vent on the front of this speaker because I had a hunch my father in law would most likely either hang them on a wall, or shove them against a wall on a table or desk, and a rear port is pretty useless at that point. I used "dualie" vents to make the design a bit more exciting to look at; a single 2" vent on the front just wasn't doing it for me. (I'm sorry I don't have the exact box volume and tuning right now. I'll have to get back to you on that.)
I built the cabinet out of 13-ply birch plywood, and did some bracing on the inside. By the way, trying to build this cabinet with biscuits was sort of a clamping nightmare...
When I had the box finished, I measured the raw drivers in the cabinet and brought the response curves into Jeff B's Passive Crossover Designer. I played around with various slopes, keeping in mind that I would have to cross the tweeter at 2200 or above. Thankfully, the Audax woofer was very willing to play ball with a variety of crossover points. In the end, I managed to get something close to a 4th order Linkwitz-Riley acoustic slope on both the woofer and the tweeter, crossing around 2200 Hz. While the woofer looks like a 1st order electrical with a Zobel, it's actually not that at all. The capacitor and resistor are being used to contour the slope woofer's roll off. When you combine this filter with the resistance of the air-core inductor, you can tailor the woofer's response in a myriad of ways (Neat trick I learned from Jeff Bagby). The tweeter filter is a simple 2nd order electrical with a resistor in series before the filter to pad the tweeter down. The Impedance curve on these is very healthy, and just barely dips below 6 Ohms; no fancy amps needed.
Here's a picture of the Vaagens during the tweaking phase. If you want to win your wife over to let you build these as your next set of speakers, this would not be the picture to show her. My wife, on the other hand, is incredibly understanding. She even helped me out in voicing these. As I was listening to them, she pointed out that they sounded a bit "muffled." I compared them to a few other speakers, and sure enough she was right. The woofer was running out of gas too soon, and there was a dip between 800 Hz and 2000 KHz. I adjusted the Low Pass filter to bring the slope up higher, and we were much happier with the result.
The overall sound of this speaker is a bit two-faced. At a quiet listening level (eg: the wife and kids are asleep), they are essentially very neutral-sounding, the Power Response is flat out to 5 KHz before it tilts down. They also have very wimpy bass. But--big but--everything changes if you crank the volume up to a moderate listening level. Once the Vaagens get to about 80 dB, they spring to life! Suddenly, the bass has a nice, healthy punch, and the system has a pleasing midrange and plenty of highs. In other words, they become exciting to listen to. Since my father in law is not the type to sit still, but rather likes to turn up some background music while he tinkers around the room, I think this design has hit its mark!
In some ways, there's no surprises here. This is a boxed speaker with a paper-coned woofer. Rock music sounds very good on them. If you're a classical fanatic, you're probably better off with something using a metal-coned woofer. On the other hand, if most of your musical collection is studio-recorded rock, country, or the like, chances are you'll really enjoy listening to these speakers. At InDIYana 2008, we were playing around with them, listening to 70's rock, and we found ourselves smiling and pulling out similar-sounding CDs: "Oh, let's listen to this one now..."
The Vaagens did not win their price category at InDIYana 2008 because they had some fierce competition, facing off against Wolf's Mn-14 (which pack a mighty punch in a small package) and a Transmission-Line MTM whose crossover was designed by Dennis Murphy (yikes!). Nonetheless, I was very proud of what the Vaagens did that day, and I have received many compliments on them. No, they're not going to be the best system to listen to Tchaikovsky. However, if you only own a handfull of classical music, and the vast majority of your collection is studio-produced and album-oriented, and all you want to do is kick back and enjoy some tunes, the Vaagens are just the thing.
Vaagen is a Norwegian name. Although us westerners want to say "VAH-gan," it's actually pronounced "VO-gan." If you go to Iowa and meet any of them, now you know how to say their last name. However, if you are in Chicagoland and you meet any Vaagens, they've changed the pronunciation to "VAY-gan." Why? I'm not sure.
I like the very Norwegian name for the speakers because my father in law is very Norwegian (just don't tell him it doesn't have any Norwegian drivers in it). The pyramid-shaped enclosures make me think of two uppercase A's, and the dualie vents remind me of an umlaut--which the Chicagoans also dropped from the name.