Lungster.Com - 3 way construction

One part of these speakers which always bugged me was the appearance of the top plate or cover. This plate covers the crossover chamber and is made of oak plywood glued to a substrate with solid oak on the edges. The edging was applied quickly and was not mitered. This left endgrain showing on the sides - ugly ! I finally got around to fixing this by making new tops for both speakers. I used 3/4 inch cabinet grade oak plywood and 3/8 inch solid oak all around. Corners are mitered and the entire top has a 1/4 inch roundover applied to the edge.

As stated in the body of the text (below), R19 fiberglass insulation was stuffed in parts of the box. The effects of this stuffing was never tested. Until recently, I had all but forgotten that I had done this. I recently removed the stuffing from these speakers, and the resulting bass seemed to be "tighter" but only by a slight amount. I don't really note any other changes in the sound, but when time allows, I 'll go back and tinker with this some more.

Parts

I started out by getting the drivers. This turned out to be the longest lead items because I waited for sales in order to minimize the cost of the project. Since I was working on another project at the time (subwoofer), this was not a problem. Both the AC-10 and 5N313 were sale items and saved me about $25 combined for each speaker. The D2905/9000 also comes in a D2905/9300 version which became available just as was going to purchase the /9000. I decided to stay with the former due to its proven reputation. The woofer came direct from AC Components, a division of ACI, while the midrange and tweeter were purchased from A&S (no longer in business).

Construction material is an area where great savings can be had without sacrificing overall quality. I browsed through Howlett's Bargain Bay, a local store that sells closeouts, recycled and reclaimed materials and found 1 inch and 3/4 inch MDF at prices below that of warehouse or lumber stores. The 1/4 inch oak plywood was purchased from HomeQuarters Warehouse (HQ) and is the single largest expense on the enclosure totalling about half of the materials cost. Shopping around on the materials can really pay off. Note that while such savings are nice, this is not an area to "cheap out" and use low cost particle board or flake board. It doesn't make sense to save a few dollar when the drivers used cost so much more. If you can't find the bargains I found, splurge and buy the MDF at retail prices - it'll make a different you can feel and hear.

Chassis

The enclosure is made is two layers - an inside MDF box and an external oak plywood layer for that finished look. I started out by cutting all panels down the size. The actual dimensions of the box was dictated by the MDF stock I had purchased. This stock came in 4 ft sheets by roughly 1 ft width. I made the outside dimensions of this box 11.25 wide X 14.75 deep X 48 inches high.

All joints are simple butt joints held with wood (yellow) glue and particle board screws. Most screw extend at least 0.75 inch into the substrate and are countersunk to keep them at or below surface level. Biscuits are used in some places for alignment but are not required. Caulking is applied to all inner seams. Looks don't count here, since the oak plywood covers everything later. Clamps (lots of them) really helps on this project !

The front baffle is 11.25 X 48 X 1 inch MDF. The rear panel is the same but in 0.75 inch MDF. The side panels are 13 X 48 X 0.75. Where the woofer and midrange are mounted, and additional 3/4 inch layer of plywood is glued onto the MDF on the inside for improved stiffness and better screw holding. There are three compartments in this box for the woofer, midrange and crossover.

The crossover is located on the top of the speaker to satisfy the goal of accessibility. A 9.75 x 13 x 0.75 inch MDF board isolates the top 3 inches into a seperate compartment. An 8 post terminals cup passes the input signal to the crossover and returns signals for the 3 drivers. Crossover components are mounted on a board and screwed to wooden standoffs in this compartment. The top of the speaker covers this compartment but is not held down with fasteners thus allowing access to the crossover. This top is 0.75 inch MDF plus 0.25 inch oak veneered plywood and solid oak banding. It measures 11.75 X 15.75 so that it sticks out the front by about the same amount as the lower skirt does. Small adjustable wood blocks on the underside of the top protrude into the crossover chamber to form a snug fit.

The midrange chamber is 0.25 cu. ft. in volume. The internal dimensions of this chamber is roughly 7 inches tall, 6.5 inches deep and the full width of the speaker or 9.75 inches. Wiring to the midrange is made via a small hole in the chamber along one of the wall which is then sealed with caulking. The lower edge of the chamber starts 24.25 inches from the bottom. Chamber walls are made of 0.75 inch MDF.

The rest of the enclosure above, below and behind the midrange chamber provides the roughly 2.9 cu. ft. space for the woofer. This space is braced in three places. The first two are at the top and bottom of the midrange chamber. Since this chamber extends more than halfway into the enclosure, bracing the rest is easy. I glued and screwed 1.5 inch wide X 0.75 inch thick plywood strips along the side and rear walls at both these locations to form part-I beams. The third bracing location is just beneath the woofer where a similar brace is used all around the perimeter of the inside. Note that these three locations correspond to the seperation between port, woofer, midrange, and tweeter.

The front baffle has 4 cutouts to hold the port and drivers. All circular cutouts were made with a circle cutting guide attached to a router and a straight cutting carbide bit. Dust collection at this point is real handy as routing MDF causes a real mess. A dusk mask is a must, and a respirator is recommended. The router jig is mounted at the center of the opening and is first used to cut the driver mounting flange. The depth of this depends on the driver used. The router is then used to used to cut most of the way through the MDF for the driver body. Don't cut all the way through since the router is attached to the middle. I used a jigsaw to finish the cut through. The port is a 5 inch long piece of 3 inch I.D. PVC pipe and is centered about 8 inches from the bottom. It's important that the hole be snug. Caulking is applied on the inside seam.

The woofer cutout is centered about 18 inches from the bottom. Note that the inside width of the enclosure is 9.75 inches but the driver is 10 inches in diameter. The outside width of the baffle is 11.25 inches. The 1.5 inch difference is used by the two 0.75 inch joints with the side panels. There are 8 mounting screws on the woofer; one every 45 degrees. When mounted, the woofer is rotated such that two screws form a vertical line on the edges. This alignment keeps the screws away from the side panels. Note that screwing into the side panels is not a bad thing; screwing into the edge of the side panel would be since it could split the panel.

The midrange center is located 28.5 inches from the bottom and offset 0.5 inches to one side. The two speakers are mirror pairs so the offset of one is the opposite of the other. This location should place the midrange entirely in its chamber. Unlike most drivers, the Focal 5N313 has a square mounting plate with rounded corners. I used the circle cutter to cut the rounded corners, drew a line connected them to form the straight portion and chisels along this line to the right depth. An alternative way would be to build a template out of plywood and use a template-following router bit.

The tweeter is offset by 1.5 inches in the same direction as the midrange. It is centered 34.5 inches from the bottom. The eventual addition of a skirt around the base will add 1.5 inches to this height placing it 36 inches off the ground.

The bottom of the chassis is made from a 9.75 x 13 x 0.75 inch MDF board with a circular cutout for a 2 post terminal cup. I used 16 gauge Radio Shack Megacable to connect the input terminal cup to the crossover terminal cup. Wiring from the crossover to the drivers was then added. All wiring is held against the walls by caulk and hot melt glue.

The sides and back panels are covered with 3 layers of 50 pound roofing felt (about 0.25 inches thick). I used a combination of caulking adhesive and roofing nails to attach the felt to the panels. R19 fiberglass insulation is then added before the chamber is sealed. The area behind the port is not filled. I didn't play with the stuffing for optimal quantity or type.

Exterior

With the inner box done, the outer oak plywood is added. This plywood has "A" and "B" sides - the better "A" side is the visible side. The plywood covers the sides and rear only, not the front. This is because the MDF I used for the front panel already has an oak veneer on it (though in the wrong grain orienation; but it gets covered by the grill). The plywood is undersized in width to allow solid oak to cover the plywood edges. I milled 0.25 inch thick solid oak for this purpose and like the plywood, is glued to the MDF box. My oak trim is about 5/8 inch wide.

Around the bottom of the speaker is a skirt made of solid oak. The skirt is about 5.5 inches tall and 0.75 inch thick. It wraps around the entire bottom and is beveled along the rear and sides. The front is not beveled due to the grill. I used miter joints on the skirt corners for the rear and butt joints for the front by mistake - use miter joints all around for a better look. The skirt entends below the box by about 0.625 (5/8) inches and is attached to the box by glue and particle board screws. Since these screws are visible, they are not only countersunk but also covered with an oak plug cut from the same oak stock using a plug cutter drill attachment. The skirt holds four 0.75 inch solid oak feet, each 2.75 inches on a side. These are glued, screwed and countersunk from the bottom. Because the speakers are to be used on hardwood flooring, self-adhesive felt pads from the local home center are added to the feet. Final clearance under the speaker is less than 1.5 inches to allow connection to the terminal cup. Wires to the speaker can come out from any side at the bottom.

The wood finish used is Watco Danish Oil in dark walnut, darkened with some Minwax Jacobean stain. Two coats are applied, followed with a coat of hand rubbed wax.

Grill

The distance from the port at the bottom to the tweeter at top is quite large. Therefore I decided to let the grill cover the entire front baffle, including the unused area above the tweeter. The grill will be flanked on top by the crossover cover and at the bottom by the skirt. The grill measures 11.75 X 43 inches and is made of scrap ash glued together and milled to approximately 1 inch in thickness. Horizontal and vertical members are doweled together and MDF corner blocks are added on the inside corners. All but the inside facing portins of the grill frame is spray painted black. This hides the frame when the black grill cloth is stretched over the frame.

Ball and socket connectors are used to mount the grill to the speaker. To allign the ball and socket connectors, I used a drill press to drill holes through the corner blocks at 90 degrees to the blocks. With the grill frame placed over the baffle and temprarily secured with clamps, I then drilled through the same holes on the grill into the baffle. These pilot holes are then used to start the final correctly sized holes for the ball (grill) and socket (baffle) connectors.

As previously mentioned, the grill is flanked at the top and the at bottom by the crossover cover and lower skirt respectively. The sides howevers are exposed thus the grill cloth is made to wrap around its frame to cover the frame itself. Due to the size of the grill, I decided not to use spray adhesive, hot glue, staples or other common method of fabric fastening. Instead my wife came up with a simple yet effective way to fasten grill cloth described in a seperate page.

Drivers

With the box done, it's time to mount the drivers. Be extremely careful with the ScanSpeak tweeter as the damping material coating the dome is extremely sticky. Dust, dirt and just about any construction particle will stick to it and be very hard to remove. I soldered a short length of wire to each driver which is then connected with the internal wiring of the enclosure with standard wiring nuts. This allows me to remove the driver at some later point without needing a soldering iron. Metal screws hold the drivers in place to complete the installation.

29-September-2000

Note: The contents in these pages are provided without any guarantee, written or implied. Readers are free to use them at their own risk, for personal use only. No commercial use is allowed without prior written consent from the author.