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| Design Goals | Driver Selection | Crossover Design | Construction | Conclusion | About The Designer | ||||
| Driver Selection | |||||
I'd been playing around with the Parts Express/Dayton 6 1/2 inch woofer for several projects. One was a vented two-way project designed for and built as an employee project for at work. This evolved into a W-T-W two-way floor standing design I built for my son. These designs also used a new tweeter from Parts Express - a 1 1/8 inch silk dome tweeter. Both the woofer and tweeter worked extremely well in those speakers and are still much in favor in an almost cult-like following on the Parts Express discussion forum at http://www.Parts-Express.com/. |
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| Crossover Design | |||
Like many of my designs, this crossover is an exercise in simplicity. It almost turned out to be a four-element design, which actually modeled and measured better, but listening tests revealed sound quality inferior to the five-element design. Particular attention was paid to the vertical and horizontal off-axis response so that the design would work well when the drivers were oriented either vertically or horizontally. You will notice the on-axis response is somewhat a departure from my normal designs in that it exhibits a rather broad dip between roughly 2 kHz and 6 kHz. This is due to the response of the Dayton Classic tweeter, and compounded by the narrow 6-1/2" baffle width. While this appears somewhat sub-optimal, in practice it sounds remarkably flat. Considering the crossover topology, I suspect the dip fills in off axis. The second order electrical filter of the woofer emulates a third order BW acoustical transfer function at 1200 Hz. The tweeter resembles, at least for a portion of the transition band, a fourth order LR at 1450 Hz. The impedance is quite high with a minimum of about seven ohms, and an average around eight ohms. Phase tracking is fairly good through the crossover region. |
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| Construction | |||||||||||||
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Construction is easy, but there are a couple of tools and techniques that will make it easier. A router with a setup for cutting holes for the drivers, i.e. a circle cutting jig, makes for a very smooth cutout, although I used a 3 1/2" hole saw for the tweeter. 1/2 inch and 3/8 inch rabbeting bits will help to cut the flush mount rabbets. The technique for that is to cut a hole 1 inch or 3/4 inches smaller than the diameter of the overall diameter of the speaker flange, then use the rabbeting bit to cut the flush mount portion to the flange diameter. Set the depth to correspond to the thickness of the speaker flange and the gasket or sealant you'll use to mount the drivers. Another technique for cutting holes that I like best of all involves the use of templates. I cut the template so that it looks just like the hole I'm trying to make in the speaker. Use 1/8" or 1/4" hardboard and a jigsaw to cut the shape. Make sure to cut carefully and sand smooth since the hole you cut in the speaker will be exactly like the template. Attach the template to the baffle with a couple of screws and, using a 1/4" router bit with bearing on the end, cut the hole. The bearing rides on the edge of the template. Note, that this must be done before the speaker is assembled. Also, it's almost a necessity to use a router table for this since there won't be much surface for the router to ride on near the edge of the baffle. Another very useful technique is to cut the front, back , top, and bottom slightly oversize (about 1/8" on each edge), then trim the overhang after assembly. For this, a straight bit with bearing is needed. I assembled the box using drywall screws and glue, but since have gone to using finishing nails instead of screws. It takes a little getting used to, but you don't have to pre-drill and counter sink and you don't have the big holes to fill. The base is very important. Combining the speaker's narrow width with its height of 4 feet, it doesn't take much to knock it over, especially on carpet. The base adds the needed width for stability. It is also a place for the crossover. Use of the spikes is also recommended. Step by Step Cabinet Construction 1. Cut all pieces to the dimensions shown. 2. Cut driver cutouts in front baffle and rabbet for flush mount. 3. Cut hole for terminal cup in rear panel. 4. Cut 45 degree bevels on interior reflectors. 5. Cut the two terminus trim pieces with 45 degree bevels. 6. Lay out in pencil the locations of the four reflectors and the divider on both side panels. 7. Glue the divider, top, and bottom in place between the two sides. 8. Glue the four reflectors in place. 9. Install foam absorption material to the top reflectors and divider. 10. Install foam to the inside of the front and rear panels. 11. Install triangular piece "G" to top of reflector "C". 12. Install piece "H" onto rear panel centered horizontally and at a point which will be 4 1/4" below the lower edge of piece "G". Note, these last two steps are done now so that the terminus can be cutout with a router using "G", "H", and the sides as guides. 13. Glue the front baffle and rear panel in place. 14. Cut out the terminus opening. 15. Install the two terminus opening trim pieces. 16. Drill wire hole in bottom. 17. Paint or apply veneer as desired. 18. Install wiring from drivers out hole in bottom. 19. Install wiring from terminal cup out hole in bottom. 20. Install drivers and terminal cup. 21. Install base and connect wiring to crossover. Step by Step Base Construction 1. Glue side pieces to top of base. 2. Drill hole for wires going into speaker. 3. Drill holes for spikes. 4. Drill and countersink holes to attach base to speaker. 5. Use 1/2" rabbeting bit to cut recess for bottom panel. 6. Cut out bottom panel to fit opening in bottom of base. 7. Pre-drill and countersink holes to attach bottom panel to base. 8. Paint or apply veneer to base. 9. Attach base to bottom of speaker. 10. Install crossover onto bottom panel and connect wires to drivers and terminal cup. Wiring It's best to install the wiring after assembly and finishing, but before stuffing the line. Run a pair of wires from each driver down and out through a 1/2" hole in the bottom of the speaker, into the base. Run another pair from the terminal binding posts down and out through the same hole. Leave about 16" extra for each wire coming out the hole. Attach the wires to the crossover and secure the bottom base cover. Note: If you plan on bi-wiring, i.e., using two sets of binding posts and splitting the crossover into separate tweeter and woofer sections, you will need to include the baffle step filter (R4/L3) in each section. That's because this filter operates on both drivers, over the entire frequency range. However, for the tweeter section, all that is really needed is R4, the 8 ohm resistor. L3, the 2.0 mH inductor, can be omitted since it provides a low pass path at around 500 Hz. Stuffing I ended up using a stuffing density of around .75 lbs/cu.ft. of Polyfil pillow stuffing. You may have heard that this material is not the absolute best to use, but it's inexpensive and readily available. Finishing Veneering is an easy and, considering the time and effort involved in an well done painted finish, an inexpensive option. A 4' x 8' sheet will cost about $60 for common paper-backed veneers such as oak and cherry. You can buy them at hardwood (woodworker) supply stores or from online suppliers such as http://www.woodveneers.com/. Even if you've never veneered before, it's not that hard. You can then stain and apply a gloss or semi-gloss finish that will look great. You can also paint the enclosure. Depending on your experience and the amount of time you want to devote to it, you can do a spray can job or create a piano black gloss finish. The Grille Here is a drawing of the grille. It is made from 3/4" MDF and covered with black grille cloth. Round over the inside and outside edges of the side away from the speaker. Before installing the grille cloth, drill a small (1/16") hole where the grille guides will go, place the grille on the speaker, and shove a small finishing nail or brad through the hole to mark the front of the speaker. Drill out the grille guide holes then install the grille cloth with hot glue or staple it in |
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| Conclusion | ||
| When I finished the db61tl, I was surprised how good $160 worth of drivers and crossover parts could sound. I'd recommend them for home theater use or for music reproduction on a budget. The speakers' bass output is sufficient for most users to consider them "full range" for music applications. At a modeled max SPL of 104 dB, they can play quite loudly without obvious distortion setting in. They are just a bit forward when the listener is on-axis, due to the diffraction bump at around 2 kHz. This helps bring out the dialog for home theater work, but for music I prefer to listen to them slightly off-axis, which minimizes the effect. |
| About The Designer | ||
| Curt Campbell has been a music enthusiast all of his life, including live performance as a trained musician. His fascination with electronics and speaker building started early with building up some oddball project or other, usually with parts pilfered from other equipment. Curt's additional hobbies include woodworking, photography, and-along with keeping the family's vehicles running-rebuilding old sports cars. He enjoys his career in commercial aviation, where he supports and diagnoses avionics systems in corporate aircraft. His current speaker building passion is crossover design, and numerous projects on the PE Project Showcase and his own website feature his crossover work. |
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DISCLAIMER - Parts Express posts the "Project Showcase" as a community service. Projects displayed have not been tested or evaluated by our staff. We make no warranties whatsoever in regard to the projects' fitness for a particular purpose. Claims of performance or fitness are those of the contributor and not of Parts Express. Project re-production for commercial resale may be a violation of United States patent or trademark laws. |
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