A Compact Sheided MTM for Just a Few Bucks
Lou Coraggio Last Update: 22 FEB2004

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Vifa BC11SG06-12
Audax TM020J3
9 Liters

6" Wide, 9" Deep
15" High
(1/2" stock)

18 November 2004

New variant, the Azurite 25 using the Audax TM025 can be found here.

22 Feb 2004 Update

I finally got back to the garage to finish these. For finishing, I chose a quick paint job. After sanding, and running a 3/8" roundover bit over all edges, I sealed with shellac. I used a spray can of satin black for a base coat. Then I shot them with a coat of the "fake rock" paint in an aqua tint. I thought they were too blue, so I used the black to mist over the rock paint and darken it down. A couple coats of waterbourne and they are done. My wife actually liked them.

Once assembled, I got a chance to sit down with them and listen to some CD's before turning them over to my wife. In final form, the bass is really impressive (from a 4" driver) holding together well into the 60 Hz region. There is a little bit of boom when near the wall. Were I to build these again I would go to 9 liters with the same port. (Dimensions above reflect these changes) This should get an F3 of 62 Hz.

After extended listening, I found that I needed to pad down the Audax for my tastes. I wound up with 3.3 ohms although 4 was very listenable. If you like it bright then 2.5. For HT, I would go 4 ohm. The TMO20J3 isn't quite as refined as the TM025, but has a definite edge in dispersion. I found the detail I expected, it just seemed slightly edgy at the very high end.

Mids are very clear and smooth. Female vocals, piano and brass all have a liquid quality that makes the Azurite sound very effortless. As one would expect with an MTM there is a fairly narrow vertical sweet spot. Close to the wall, the soundstage is fairly flat. Move them out a couple feet, and the image blooms into deep soundstage that holds up well off axis.

The Azurite is fine standalone speaker for small to medium sized rooms. Most folks would be very happy with 5 of these for HT. Better get these drivers while they last!

31 JAN 2004

I swore I was going to lay off those clearance drivers at Parts Express. Despite all the PE claims to the contrary, I never really found the right driver for that once in a lifetime investment in a reasonably priced line array. Until this little vifa BC-11 came around. I've used the Vifa BC/TC drivers in other designs and I've been quite pleased with the performance.

I've never been a huge fan of MTM's. Keeping impedance and box size reasonable with two parallel drivers isn't always an easy task. The main motivation for these came from my wife. We have a nice TV in the bedroom that has a built in 10 watt amp for external speakers. The entertainment center has room for a pair of 6" wide speakers. The Azurite will fit nicely into place, provide a friendly load for cheap electronics, and sound pretty good. [Before you ask, I cannot talk her into a complete HT setup. She is electronically challenged and intimidated by remotes!]

The boxes were designed for an MTM variant of my nugget monitor. They are 8 liters, (about 485 cu in net) tuned with 1-7/8" I.D. x 4-3/8" port (PE 269-920 ). I used 3/4" MDF for the baffles, and 1/2" else where. Just a couple of small braces around the middle of the box. The box is a wee bit small for the BC, but it sounds just fine. [IMHO, people smother too much about tuning boxes]

I spent quite a bit of time on the crossover design, as I really wanted to push the Vifa all over the map. [I am actually planning a line array with these!] I took both free air and ground plane measures.

The basic design is a 2nd order electrical in appearance. Crossover is about 3850 hZ

I found no need for a zoebel. The 13.6 uF value is easily built with two 6.8 caps in parallel.

I used two 3.3 uF caps for the tweeter section. You could replace them with a single 6.8 and feel comfortable.

The 4.7 uF cap provides shaping for the rising response of this tweeter. I used 3.3 ohms for the padding resistor. A 2.5 will be on the bright side, A 4 would be better for home theater.

I wanted a slightly pronounced midrange to help with TV dialog. After listening to the prototypes, I was really enchanted with sound of these. The Tangband used in the Nugget is a bit crude by comparison. Mids are sweet and liquid. The high crossover point makes it a bit easier to adjust padding. I am waiting for crossover coils, so I can't really comment on imaging and placement.

The bass is very tight down into the 60's. There is a definite bass attack present. There's not quite the thump that I have in the Garnet, but the mids in the Azurite are sweeter. Predicted impedance does not drop below 5 ohms with a peak of about 20 ohms. I would have no problem calling these 6 ohm (nominal) speakers.

I think these are as good as, (or maybe better than) my Topaz design. Certainly the Topaz tower had better bottom end, but the mids on these are truly silky. The better dispersion of the 3/4" Audax, and the additional breathing room afforded by the higher crossover make the Azurite a bit more "effortless" in reproducing music.

So why build these? Great quality for cheap (<$50 each!) Nice, small size. Exceptionally smooth sound, impeccable shielding and amp friendly load. Both my wife and daughter said they liked the teal driver color. Even my wife said I didn't need grills. (High SAF)

With the limited availability of these Vifa's, and the Audax sale. You might want to pick up the drivers. When I finish a pair with "real" components I will expand this page.


255-250 1.0 Coil $3.78 255-020 0.1 coil $1.78
027-424 6.8 cap (3) $6.75 027-422 4.7 cap $1.89
004-3.3 Resistor $1.25 276-102 Audax Tweeter $8.04
299-433 Vifa Woofer (2) $19.54 269-920 Port Tube $0.47
260-301 Terminal $1.95 TOTAL $45.45