We were granted a reprieve from Al Gore's doomsday scenario, and had a couple of breezy days with highs in the 90s. (In June, for the AZ desert, that qualifies as sweater weather) I was able to get some measurements. I used a single point on vertical axis with the tweeter. The mids were measured as a single driver. I usually set up about 5-10 degrees off axis horizontally. There are some clear wobblies in the tweeter response that I attribute to box edge diffraction. In keeping with the "cheapskate" intent, I worked up three crossovers with varying degrees of baffle step and woofer inductor values. The box is lined with mattress topper and a couple fistfuls of dacron batting.

With 3-4 dB of baffle step and an iron coreon the woofer, they sounded tubby and bloated. Too much bass!? I worked through two other crossover versions before settling on this configuration. BSC models at about 2 dB. The crossover is about 3100. Judging by the consistent phase alignment at varying model distances, this seemed "right" and natural sounding. The pseudo zoebel in the woofer circuit helps tame a bit of a peak in the 1000-2000 range. When coupled with the 2.4 on the tweeter shunt coil, everything flattens out nicely. The split padding resistors help tame some of the wobblies in the tweeter response. (NOTE: IMO, this design does not need a recessed tweeter, nor does it need an offset. I've compensated for those in the crossover. If you choose to "improve" the design, you are on your own.) If you want to play with tweeter padding, I'd suggest 2.7 or 3.3 ohms on the last resistor.

Aug 9, 2010

The buyout tweeter I used is sold out. Based on comparo's done by Johnny Richards (Thanks Johnny! ) on the PE Board it looks like the stock Vifa BC25SG15-04 (#264-1026) should be very close replacement. I think the buyout version may be a tad bit more sensitive. So I'd suggest something in the 2.0-3.0 range for the final padding resistor. Season to taste.

When somebody uses this and let's me know what they found, I'll post it here.

Listening Impressions

It's pretty rare for a design to exceed my expectations. LECBOS certainly does! Even with the reduced BSC the bass line is clean, tight and articulate. If these roll off at 70, then I've certainly been fooled. I'm sure I'm hearing harmonics from that lowest octave, but they sound like they go a lot lower than than they model. Dual woofers still move a lot of air even without a lot of throw. The Peerless handle male & female vocals equally well, with a very sweet, forgiving quality Some of the nicest midrange I've heard in awhile. (There's something about paper woofers...) Well engineered recordings are clear & clean. Crap mastered pop is tolerable and doesn't send me to the volume control.

The BC25 is exactly what I've come to expect from Vifa silk domes. Nicely detailed, airy, very sweet. The very top sizzle is a bit muted when you get aways off axis, but cymbals and percussion are very clear.

The sensitivity goes a long way to covering the limited driver Xmax. With nearly flat impedance profile hovering around 8 ohms, even the cheapest receiver, or low wattage bottle amps should be happy. For most folks 20-30 watts ought to make your ears bleed. With bass management and a sub, even metal heads should be happy.

June 19
I sanded the boxes, slathered on a couple coats of Duratex, and finished the final buildout on these. I sat down to listen for an extended session. I usually run an old NAD preamp, a Dayton APA-150, and an old Yamaha changer out in the shop. Today I ran LECBOS with the Dayton DTA-100 T Amp as well. (Looks like I can put my entire measuring setup in a single briefcase now!) Both pushed these with no hint of strain well into the high 90s. I thought the APA-150 was a bit sweeter and more forgiving, but the DTA 100 is one impressive piece of gear. Like other T-Amps I've heard, this one tends to add a bit more sizzle to the top end. I thought the tweeter padding was just right with the APA-150, but might bump that 2.7 to 3 ohms if I was using the brighter DTA as my main source with no treble controls. I gotta admit, the power and clean output from that little DTA is really impressive! I never realy ran it more than half gain to get them as loud as I could tolerate.

Move the LECBOS back near the wall, and I would be quite happy without a sub. There's a slight hint of muddiness when they are cranked up very loud and the source material has a lot of synth bass, but I could easily live with the bass they do produce. Very nice wide soundstage. Vocals & brass are very clearly reproduced. The gain in bass from near wall placement, does flatten the depth of the stage, but that is an expected compromise. Like most MTMs, vertical, off axis position changes the character a bit more than horizontal off axis listening. The tweeter will take just about all the power I could stand and holds up nicely at 20-30 degrees off axis. These boxes are as clean and clear as any MTM I've built. With the benign impedance curves, high sensitivity, and driver quality, I'd be happy with these at $250 a pair in parts.

LECBOS isn't just a great speaker for the money, it's a damn good speaker, period. Get 'em while they're available...

July 4, 2010 Update

Today I finally hung the LECBOS on the garage wall. I also hooked up an AutoTuba I built long ago. I ran the sub with an MCM clearance plate amp that has a 5 db boost at about 35 Hz. I'm not sure where I crossed the sub but I'm guessing about 60 or 70. The LECBOS are running full signal. With a sub, I now have as good a garage system as I could ask for. Nice wide soundstage, great mids, imaging holds up off axis. As with any wall mount, the compromise is less depth of stage.

By the time I cranked things up to ear bleed level, I thought the tweeter got a little edgy (my neighbor came over to check them out (they sounded good in his back yard in the pool). A slight cut at 7KHz on my preamp cleaned up the edge. Soo... if you are planning on wall or near wall (particularly in a bright room at high levels) I'd suggest using a 3 or 3.3 ohm for that final padding resistor. (I wound up with a 3.3 ohm in final form as shown) Based entirely on my experience of listening while working around the shop, I couldn't discern any dramatically noticeable differences standing, seated, or considerably off axis. This would lead me to conclude that most would find the LECBOS acceptable as a center channel.