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A Version of Bert Doppenberg's TQWP speakers
Just for fun, I decided to try and build a TQWP speaker using small full-range drivers. I started with Bert Doppenburg's TQWP design, which was published on BD Design's web page, and used el cheapo Radio Shack 40-1197 drivers.
The result was really astounding for drivers that cost US$5.00 each. Not perfect, though.
I modified the design to use the 40-1197 full-range as the front (main) driver, and put a small PVC-cone woofer, the Radio Shack 40-1030, in for the rear driver (nicely, they fit in the same hole as the 40-1197). This helped the speaker quite a lot, filling in the midbass and pumping up the bottom just a tad.
Next, I bought a pair of Fostex FE108 Sigma's and installed them as the main drivers (also the same hole as the 40-1197!). This made the speakers a tad bright.
The sound of these little guys has improved with time. As they broke in, the brightness has disappeared. The amount of bass generated from such small drivers is surprising. In a small room, I don't find them lacking at all!
All in all a good project.
The plans for this project are no longer available on BD design's web site. I asked Bert Doppenberg if he would let me post them here, so others can build their own version of this speaker. Bert graciously agreed, so here are his plans. Click on the pictures for a full size drawing. Thanks Bert!
Bert also designed a filter to shape the frequency response a bit. With the drivers I used, I found I didn't really need it... but if you'd like to enhance the bottom end and tame the "brightness" a bit, especially with a pair of FE103 drivers, try this circuit: