A friend of mine asked me to do a custom Home Theater design for him. Nothing too ostentatious, but he wanted it to be competitive with the boutique brands in the 4-figure range. After toying with a few various cabinet shapes, we agreed on a pair of MTM mains, TM surrounds, and a W/TM/W center channel. This is how it all came out looking....
The cabinets are veneered in paper-backed mahogany, and were finished with Formby's Tung Oil, rubbed on in like a zillion coats, then briskly rubbed out with Paste Wax and steel wool.
I did a "build log" of this system at HTGuide as I went along. You can read it here.
My friend chose the HiVi M-series drivers because he liked the looks of them (who doesn't?), and I felt confident that they would perform very well based on my very positive experiences with other concave metal-cone drivers by HiVi.
For a tweeter, I wanted something with a small footprint to allow for close driver spacing. I tried a few of the small neo tweeters out there and finally arrived at the Dayton ND28F. I was hesitant to try this driver, since I am not a fan of the Dayton DC28F "Silkie." However it turns out that this tweeter is nothing like the Silkie. The ND28 plays cleanly, does not introduce any of its own hash or FR irregularities, and simply disappears. It's also very easy to work with in a crossover, as it reacts predictably to changing component values, and does not require much more than a simple 2nd order electrical filter to achieve a nice 4LR acoustic slope.
Swope MTM as built by [PoorboyMike].
Swope MTM as built by Harold. The outside boards are Oak, which is dyed using the traditional "steel wool dissolved in vinegar" method. The inner section shows the inner plies of plywood--a "vertical translam," if that makes sense. He claims he was inspired by cjd's Ansonica project.
These have surprisingly deep bass, image well, and should have a sensitivity around 87 dB.
Here are the basic cabinet plans. Note that the slot is 1" tall.
Crossover and component layout. Beautifully minimal parts count!
The Frequency Response shows a dip at 450 Hz. This is a measurement artifact; ignore it.
The impedance phase angle goes a bit farther than I'd wish at 2000 Hz, but it's a 4 Ohm speaker, so it'll need a more robust amp regardless.
Finally, here's a quick Bill of Materials
These are sealed boxes; approximately .25 cu ft. In fact, they should be the exact same size as the Parts Express pre-built cabinets. Because these are sealed, the bass rolls off beginning at 70 Hz. Nonetheless, they actually sound decently full as standalone bookshelf speakers. Otherwise, similar voicing through midrange and treble on these as the MTMs.
Crossover and Bill of Materials
Here is the final Frequency Response of the TM. Overall, very well-behaved and very pleasing for long listening sessions. The midrange is voiced slightly relaxed so that you don't want to tear your ears out when listening to less-than-perfect recordings.
Here's the Center Channel, looking a little rough around the edges.
The Center Channel is sealed, and has a small sealed chamber built within it. Please take note that the driver spacing on the front baffle is very tight (within 1/4" inch in places. Be sure to measure carefully--draw it out with a compass if you have to--before you cut any holes.
Crossover and Bill of Materials.
Please ignore the extra wiggling going on below 200 Hz in this graph. This was measured in-place (on a TV stand, under an actual TV), which is not going to look as smooth and pretty as something measured under perfect anechoic conditions.
The load of the CC may be a challenge for really cheap amplifiers, as it dips just below 4 Ohms between 100-200 Hz. There's nothing we can do about this, however, since the woofers are run in parallel. Most mid-fi Home Theater amplifiers (Onkyo, HK, Marantz, Yamaha, etc.) should have no problems running such a load, though.
See, this is Hi Fi. OK? Hi Fidelity. You know what that means? That means this is the highest quality fidelity. Hi Fi: two very important things to have in a stereo system.
(c) Paul Carmody | this page was last updated January 1, 2012