Initial Wiring

Here we just want to get the basics of the wiring in place while we have the best access to the box.

21. Using screws, install one of the 12" drivers into the Isobaric Chamber.

Tip: Use the speaker sealing caulk around the rim of the speaker to ensure an air tight seal.

Tip: Don't slip off a screw head and puncture the speaker with a power drill –again, not that it ever happened to me!

22. Mount the electrical connections in the Isobaric Chamber. Referring to the adjacent picture, mount the Matchit Autoformer in the center, one pair of binding posts on the left, two pairs of binding posts on the bottom right, and the grounding blocks on the right wall of the Isobaric Chamber.

Tip: If you decide to move the mounting locations, make sure that any connection wire will not rub up against a driver (unless you enjoy random buzzing of course).

Tip: Since the binding posts will mount through the sides of the Isobaric Chamber, glue each of the posts in place to ensure a tight seal.

Tip: To start, use the 4x connection in the Autoformer.

23. Label the various components you just installed. The left pair of binding posts should be "External Speaker Input". The right two pairs of posts should read "Isobaric Voice Coils". Finally, the grounding blocks should read "Internal Speaker Distribution"

Tip: If the binding posts used are not color code, you may want to note polarity ('+' and '-') as well.

24. Inside the Isobaric Chamber, using some 12 gauge speaker wire, connect the "External Speaker Input" to the Input of the Matchit Autoformer. From the Output of the Matchit Autoformer, connect to the copper grounding blocks. The connections to the two copper grounding blocks will need to be soldered.

25. Outside the Isobaric Chamber, solder enough wire to the posts labeled "External Speaker Input" to allow connection to the binding posts on the back of the box. Also, connect the posts labeled "Isobaric Voice Coils" to the 12" speaker (one pair per voice coil).

Tip: At this point, you're probably wondering why mess with all these binding posts, and why not simply connect to speakers directly? Well, there are a couple of reasons. First and foremost, this method allows us to customize the impedance seen by the amplifier. With four voice coils and the Matchit Autoformer, we have quite a bit of flexibility. By adding or subtracting voice coils, changing to series or parallel wiring, adding some kind of damping circuit, we can tune the response of the box to any system by simply removing the front driver. As a side benefit, the binding posts allow for a nice tight seal of the chamber.

Assembly

You've been patient; let's see if we can make this thing look like a speaker.

26. If not already done, disassemble the main box.

27. So that the two drivers are concentric, screw and glue the Isobaric Chamber (with speaker attached!) to the back of the front panel.

Tip: Use LOTS of wood glue when you assemble. When you press panels together, there should be a bead of glue oozing out the entire length of the joint. This is to ensure that we get a tight seam and there are not voids in the glue bead. Once the connection is completely screwed (hah!), wipe off any extra glue.

28. Using the Spray Adhesive, apply the acoustic foam to All interior surfaces of the box and let dry.

Tip: Stop approximately 1" from each panel edge to allow room for assembly. In final assembly, the adjacent foams will join to a single piece where they meet.
Tip: Spray both the panel and the foam with the adhesive and allow it to become tacky before applying.

29. Once dry, cut out relief holes with a utility knife for the ports, binding posts etc. to allow them to pass through the box.

30. Screw and glue the sides of the box together.

Tip: Cover the driver in the Isobaric Chamber to keep it from getting any glue on it.

31. Take one of the 1" dowel rods you cut to length earlier, coat the ends of the rod and the 1" holes in the left and right side of the box with lots of Gorilla Glue.

32. Insert the rod through the holes in the box.

Tip: Once inserted, make sure that plenty of glue is on there to keep a tight seal.

Tip: Rotate the rod in place to distribute the glue.

33. Repeat the previous step for the second rod.

34. Insert the 2" flare ports through the two openings in the top of the box. TAPE (not glue) the top of the flared ports to the remainder of the port to keep it from sliding in the box (if that happens your day will be ruined).

35. Screw and glue the Top of the box to the sides.

36. Install the WBT speaker posts to the back of the cabinet.

37. Solder the connection from the WBT speaker posts to the binding posts on the Isobaric Chamber labeled "External Speaker Input"

38. Let the assembly dry.

Tip: Read a book, take a nap . . . .

39. Flush cut the ends of the dowel rods with the box panels.

Tip: A flush cut pull saw is your best bet here.

Tip: When you run your hand over the panel, there should be no "bump" when you reach the dowel.

Grilled to Perfection!

To protect the driver from damage, I added a simple grille. To make it look pretty, I followed the proportions of the main box.

40. Using some scrap ¾" thick hardwood (i.e., oak), cut into ¾" wide strips.

41. Cut to the frame sides to length.

Tip: Remember the 5 degree angles used on the main box apply here as well.

42. Lay out the frame, butting the edges together.

43. Pre-drill the frame for the same screws we've been using.

44. Screw and glue the frame together and allow drying.

45. In the four corners of the grille, drill a hole for each ofthe magnetic screw guides.

46. Centered on the speaker cutout in the front panel, drill four holes at the same relationship to one another as the holes in the speaker frames.

47. Using Gorilla Glue, mount the magnets in the frame and on the box front panel.

Tip: Mounting the magnets to the front panel now means that they will be hidden by the veneer – fancy!

Tip: Make sure the magnets are pulling towards one another when they face each other!

48. Doing your best to keep the fabric from bunching on the frame, stretch the grille cloth over the frame you just constructed and staple into place using a heavy duty stapler.

Click Here to Go to Part VI.