MONITOR 890 MK III
This octagonal cabinet looks more complicated than it really is. All the chamfers are cut at 22.5° except two (at 45°). When you set up the saw, it is best to cut fractionally over 22.5° to ensure that, on the outside, all the chamfers are really airtight.
First cut the required cut-outs in the boards, which have already been cut to size. The two circular ones for the bass loudspeakers, the square opening for the tunnel and the two for the level controller.
Next, build the main body without the base and top. You will need plenty of sticky tape to hold the joints together when gluing the side panels. The parts for the tunnel, the four stiffeners on the side panels and the vertical stiffeners (50 mm wide) on the front baffle then need to be shaped to an exact fit. The base then has to be shaped to fit exactly in the completed main body, since it is hardly possible to build the body with millimetre accuracy. Next, glue the vertical stiffeners to the base and the stiffener between the baffle and the rear panel.
The top with its cut-out for the terminals for the high- to mid-range is then shaped to fit and glued in position. The two crossover circuit boards are attached to the rear panel opposite the lower bass speaker drivers. The wiring to the horns need not be heavier than 1.5 mm². From the terminals to the circuit boards and to the woofers, use wires with a cross-section of 2.5 mm².
The twin terminal unit for connecting the mid- to high-range horns is fitted in the square cut-out in the top. The two gold-coloured jumpers have to be removed to do this.
The mid-range horn is placed on top of the cabinet on its three straight-sided feet. The tweeter is mounted on the wooden base supplied and is placed on top of the mid-range horn, towards the rear. The position of the two horns is crucial to the acoustics and, for this reason, they should be positioned as shown in the drawings.