|Project by ferstler||posted 02-19-2010 11:54 PM||3588 views||8 times favorited||10 comments|
In an earlier article I discussed how I had built the left and right speakers for my smaller home A/V system. The center speaker in that installation, built to match some Dunlavy Cantata left and right speakers used there for a while, was different and not really stylistically compatible with the new left and right mains.
The new center is built to match the new left and right units I built to replace the Cantatas. The top, bottom and sides are select pine and the front and back are mdf. Different woods in a speaker enclosure are a good idea, because it helps to break up resonances inherent in one type of wood. The cabinet is 38 inches high, with a 4-degree backward slope to the front. The width is 7 inches and the depth at the top is also 7, with 9 inches of depth at the bottom.The front is angled back because the midrange and tweeter drivers are arranged in a vertical MTTM array, and that kind of configuration tends to focus the output vertically, helping clarity and detail. You want the “beam” to be aimed at seated ear height; hence the angled front. (The left and right speakers I built earlier are each four feet high, and the MTTM arrays are themselves centered at seated ear height, which means no front-panel sloping was needed.) The horizontal dispersion of the driver array is very wide, however, which is what you want for good sound propagation.
The first picture shows partial assembly, and also shows the woofer and one each of the tweeters and mids, along with the double connector cups that would be mounted on the back.
The second shot shows the front/back clamp up. Interior moldings were first glued into position and then the front and back were glued to them. For both gluing jobs I used PL construction adhesive, because it is thick enough to both glue and also seal any potential air leaks. Large cutouts in the back allow for the two crossover networks: low-pass for the woofer down below, and high and low pass for the tweeters and midranges in the top section. A baffle board separates the upper and lower sections, thereby isolating the open-back midrange drivers from pressures generated by the low-mounted woofer.
The third shot shows the stained, urethaned, and painted cabinet before the drivers and networks were mounted. The cabinet interiors (upper and lower) were filled with echo-damping polyester fill before the components were installed.
The fourth shot shows the two crossover networks after completion: woofer network to the left, tweeter/mid network to the right. They are each mounted on 3/4-inch pine boards that were themselves screwed and glued to masonite pieces. The masonite is slightly oversized in width and length, and drilled out on the edges to allow screws to secure the removable boards to the back panel. Gasket tape insures a good seal. These sections are electrically coupled together in the finished system by long jumpers in the back. Removing the jumpers would allow the system to be biamped. I opted for just a single amp, however. All wiring here is done point to point, because I have an aversion to those printed circuit boards one finds advertised for building circuits like this.
The fifth shot shows the finished speaker, with the grill not installed. The grill itself is made out of thin wood framing, with cloth stretched over it and glued in place, and with velcro tabs for attachment to the cabinet front. I cut the framing sides for the grill assembly out of an old broom handle (using a band saw to quarter the dowel lengthwise), because the hickory wood they are made of is stiffer than the pine used to make typical quarter-round moldings.
The sixth shot shows the new center in place, flanked by the previously built left and right speakers.
All three of these speakers are decently flat responding in terms of room/power output (I use a 1/3-octave RTA to validate this), and they are also electrically equalized for ruler-flat final response. All three have been compared to the Allison IC-20 systems in my main installation and the similarities in performance are remarkable.
The subwoofer shown in the final photo (the sub has a big stuffed bear on it) is a Hsu VTF-3 (MK) that extends the low end of the multi-speaker package down to 20 Hz, flat and smooth.