It has been a long time since I have worked on a speaker project. I have lots of parts sitting in boxes, just longing to become a full, functional speaker! So this holiday season I decided to get back onto the horse and finish up Speaker III. The first step is to figure out where I left off.
The first problem is the shielded tweeter. I only bought two, and they are not available anymore. This is not a bad problem – LCDs are the norm today and magnetic shielding isn’t as desirable as when I started Speaker III in 1998. I found a substitution in the way of the Vifa D27TG-05-06. It is a silk dome with ferrofluid like the D27SG-05-06. Efficiency is similar between both units at 91/92 dB/2.83v, as is the resonance frequency of 1,000 Hz.
It is a lot of work to make your own cabinet with the number of small internal pieces. So I decided to use a pre-fabricated MTM (mid-range / tweeter / mid-range) cabinet from Dayton Audio. Internal volume is 0.75 cubic feet. The front baffle is removable and ready for your driver cut-outs. Here is the Front Drawing with tweeter and mid-range locations and cut-outs. Note how the lower mid-range is further away from the tweeter than in Prototype #3 (I will show why this is not good later in testing).
Well, I didn’t save myself that much work. I wanted to do a round-over on the mid-range cut-outs based on my research into cleaning up the tweeter response. I couldn’t find a router bit that would let me do that – not at a price < $100 anyways. The solution was to make my own baffles out of two pieces of half-inch particle board and glue them together after making all the routes and holes.
Where did the work come in? Trying to finish the baffles as nicely as the factory baffles. To achieve a smooth finish I coated the baffles with an epoxy product. Which I then sanded. And then applied another coat. And sanded. And again. And again. Then I finally sprayed on a black laquer.