DCT = Dispersion Control Technology
The inspiration for this design came from the realistic 3D sound I enjoy listening to when I have two small drivers facing upwards on a desk during driver evaluation. I also had a desire to build a system that didn’t have a crossover point where the human ear is most sensitive (2-4 kHz).
The design is a 2-way floor standing system with semi omnidirectional dispersion. The wide dispersion is accomplished by firing the high frequency driver in a mostly upwards direction. An acoustic lens and reflector focus the sound semi Omni directionally.
Design a system that provides realistic sound that most people could enjoy listening to with the total driver cost being less than $200.
The full range driver has its own sealed chamber at the top of the enclosure with a cone shaped section behind the driver to reduce the back wave reflection affects. The woofer is a Peerless 6-1/2 inch HDS Aluminum cone. Due to the systems low 1 kHz crossover frequency, I could take advantage of the reduced mid-bass distortion that and aluminum cone offers without the need for an electrical notch filter to suppress the cone break-up resonance.
The shape of the enclosure is very much a form follows function type of design. The enclosure is made narrower at the rear so that the surface area on the top baffle farthest from the full range driver is reduced. The wall are non parallel to hinder the creation of standing waves. The geometry of the folded MLTL was designed so that the exit ports crossed the line path to provide the rear exit. The extra side panel detail allowed the main panels to have cut outs to increase the MLTL cross section area where the ports cross and make the panel stiffer and heavier. The front vertical baffle round overs help smooth baffle refraction and make the front baffle narrower increasing stiffness. The alignment for the woofer is a folded Mass loaded Transmission line with two 1-5/8″ ID ports on the rear panel. The transmission line also has a separate chamber at the bottom tuned to suppress unwanted line resonances. The full range driver is housed in its own sealed compartment that has a cone shaped section behind the driver to help reduce standing waves.
The exterior panels are 18mm baltic birch plywood except for the top baffle that is solid Qtr. sawn white oak and the black painted side panels are 1/2″ MDF. The internal partitions are 1/2″ baltic birch plywood and the cone section of the full range enclosure is two cardboard cones from a craft store glued together to increase strength. The enclosure panels are put together wood glued miter or butt joints. After I built the prototype enclosure and had issues with aligning the panels I built fixtures to help align the panels for the final version. The vertical round overs are made by cutting a section out of a 3″ ABS drain pipe that was epoxied to the chamfer panel behind it.
Designing the crossover was done rather unconventionally. I started using the PCD spreadsheet and had to set a large offset from the baffle for the tweeter (full range in my case). I started with 1st order electrical slopes and found that I could combine the woofer baffle step compensation with the low pass filter by using a larger 5mH inductor. A ERSE Super Q inductor was chosen for lower DCR to not overly affect enclosure tuning. The simulated crossover was about 600Hz and a flat on axis response was possible with a single capacitor on the full range driver and inverting the phase like is usually done with linkwitz-riley circuits. After tweaking the crossover frequency is closer to 1kHz.