These speakers are the largest I have made to date measuring approximately 1.5 cubic feet each. They are also the most powerful, with eight full range drivers providing a large sound stage and a subwoofer in each speaker reaching 45 Hz with no drop in volume and still usable to 30 Hz with room gain.
For this project I wanted to build a set of stereo speakers which would cover the full frequency range themselves, as opposed to a 2.1 system using two stereo speakers and a separate subwoofer. This resulted in the power of a set of tower speakers in a comparatively small unit.
These speakers were not straightforward. This may be in part because I decided I wanted to do something with these eight 2 inch drivers and 6.5 inch subwoofer first. It turned out these were not a perfect match for each other and needed some extra work. Typically, a simple crossover network would be used to low pass filter the subwoofer and high pass filter the other speakers such that they each played their bandwidth of frequencies. However, on the first assembly the output level across the frequency range was far from even. I experimented with different crossover frequencies, using L-pad enumerators to bring down the overall level of the full-range drivers, adding a partitioning wall to isolate the subwoofer, and stuffing the full range enclosure to reduce resonances.
The final configuration splits the full range drivers, with two playing fullrange and two high pass filtered at 800 Hz. The subwoofer is low pass filtered at 500 Hz which is higher than a subwoofer should be, but in this case the driver is able to handle the low midrange and eases the transition to the other drivers. All the square fullrange drivers are attenuated with a variable 8 ohm L-pad.
The graphs below show in green the subwoofer chamber response, in white the response of all four full range drivers, and in red and orange a pair of the drivers and a pair of filtered drivers. The software and real testing confirmed each other and allowed me to make more informed predictions before trying future configurations.