|Project by ferstler||posted 09-16-2012 03:06 PM||1314 views||0 times favorited||1 comment|
In the past, I have done project articles here for some bookcases in my AV room, an audio equipment cabinet for that room (made out of cedar and mdf), some Sonotube cylinder subwoofers also built for that room, and some pine-finiished, floor-standing satellite speakers that were built even earlier, but which became cosmetically out of place for that room once the other items were complete. Those original satillite speakers are now cosmetically upgraded to fit the room decor. This photo series and commentary tracks that upgrade.
The first photo shows the full result, with the three bookcases across the front, the cylinder subwoofers in the corners, and the three “reclad,” floor-standing satellite speakers out in front of the bookcases. (I even made the picture frames, and the photos, too; the stuffed animals belong to my wife.) The cedar equipment cabinet is to the far left. (The small speakers in the upper left and right corners are two of the six surround speakers in this AV installation.) The floor-staning and flanking left and right speaker systems are each four-feet tall and the center speaker is three-feet tall. Each contains a vertical MTTM driver array near the tops (mid, tweeter, tweeter, mid), with two 5.25 inch woofers near the bottoms. The midrange drivers are all made by Tang Band (from China), with those in the left and right units being 4.5 inchers with phase plugs to improve dispersion and with those in the center unit being 3 inchers (also with phase plugs) to keep the line array short enough to fit comfortably into the shorter cabinet. The front of the center speaker is angled back 4 degrees to keep the array aimed at seated ear height, but no tilt was required with the taller left and right units.
The second photo shows the left speaker before the “recladding” work. The tweeters are Allison RDL units that have super-wide dispersion (these are no longer made) and the woofer is a 6.5-inch Allison unit. There is an interior partiition between the upper and lower sections to keep woofer pressures from interfering with the midrange driver performance. While the pine finish of the enclosure looks OK, it is not furniture grade.
The third photo shows some of the bench work, done outdoors on a workdeck that is adjacent to my small, but tidy and well-organized woodworking shop. At this time, the basic cladding is done. The original front, mdf panel has been cut away some (removing the old cutout holes), and a new panel, also made of mdf, has been glued and screwed over it. The glue used was PL construction adhesive. The first layer had to be cut away somewhat, because mounting open-back midrange and woofer drivers on material that was ultimately 1.5 inches thick would crowd the the rear sections of those drivers too much. They need some “breathing room” back there. Note the new woofer cutout holes. This was done, because the 6.5-inch Allison woofers were going to be replaced by dual Dayton 5.25 inchers. Doing this would double the power handling, because the individual voice coils of the Daytons were the same size as the single coil in the Allison. The total cone area was also increased by 20%. These drivers, which are rated to get down to about 60 Hz, only need to get down to 90 Hz, where the systems would be crossed over to the subwoofers. The side and top “cladding” is redwood, reclaimed from a now-retired old friend who had been using it since 1980 to hold his model train collection. It had previously been varnished, and after planning off the stuff the clean redwood boards were 5/8 inches thick. Over the 3/4 pine, that made the panels (glued together with Elmer’s carpenter glue) about 1 and 3/8 inches thick.
The fourth photo shows the loose drivers (only one woofer is shown, with the others in the boxes to the right) and the crossover networks. Each system has a low-pass section (second-order filtering) and a separate section to handle the high- and low-pass requirements of the mids and tweeters (also with second-order filtering). These circuits are glued to pine boards that are glued and screwed to Masonite sheets that will be fitted into openings at the rear of the cabinets and held in place by screws, making them removable. The boards would be electrically connected together by short cables on the exteriors of the back panels, with the inputs from the amps connected to the bottom networks.
The fifth photo shows the now stained cabinets, with the masking still in place. The stain was Minwax red oak, and five coats of Minwax gloss spray lacquer was put over it. Minwax recommends a 5- to 15-minute “soak” with the stain, but redwood darkens quickly, so I only left the stain in place for about a minute before wiping off. Prior to the staining work I used Minwax prestain to minimize blotching. You can see the rear panel of one of the speakers on the left, with the openings for the crossover mounting.
The sixth photo shows one of the finished speakers; the same one that was in photo number two before the project began. Note that the dual woofers have replaced the previous single woofer and the light-grey frames of the midrange drivers have been painted black. The silver-colored, solid-aluminum phase plugs have not been painted, however. The upper chambers of all three speakers are loosely filled with polyester fill and the lower chambers (woofer chamber) are filled with fiberglass batting. The batting acts as an acoustic heat sink that actually simulates a larger interior space.
The earlier versions of the speakers were terrific performers and the reclad versions are just as terrific sounding and look much better.