Main Line Arrays

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The main left/right speakers are "near" infinite line. The array is 8' tall mounted 1' off the floor thus leaving a 1' gap between array and boundary at each end. There are eighteen Dayton Reference 6” truncated frame mid-bass drivers and forty two 2” Aura mid-tweeters in the array. Originally no shading was used but with encouragement from Don Keele I later added Hann shading to the array. I no longer believe that shading is the best approach nor is CBT. (Sorry Don) I believe instead that in a situation where a true infinite line is possible, it is the better approach. Problem with any line array other than CBT is that they only work well if the listening position is in the center. With an infinite line, no matter where you are, you are in the center so problem solved. Where infinite line is not possible however, CBT is definitely the best approach. I view the CBT as the perfect solution for finite line arrays, in fact CBT is really the only mathematically correct way to build a finite line array.

The eventual replacement for the existing speakers will be a true floor to ceiling (or at least as near to this as is practical to install) infinite line array with no shading. I would also like to make the new design a three way adding tweeters that can be crossed into around the 3 ~ 4 KHz range. The new speakers will likely remain open baffle with Owens Corning 703 insulation in the back opening of the enclosure just like the existing speakers.

To mount the 2" Aura drivers I just glued them in place with RTV. The 6" drivers are compressed between foam tape gaskets and rubber grommets. As you can see in one of the construction photos the grommets simply go between the driver flange and an aluminum bar that holds everything in place. This actually worked out quite well!

Construction photos:

One note about the 2" Aura drivers. These are little reverse domes with a very large pole vent being the only escape to the outside world in the rear of the driver. This vent along with the air mass behind the reverse dome forms essentially a ported baffle tuned to about 1,7 KHz. If used in open air this driver has a very large 1.7 KHz peak as a result. The peak can be eliminated by mounting two of the drivers back to back and wiring them out of phase so they work together as a dipole or it can be eliminated by mounting damping material like the Owens Corning 703 to the back of the driver. In the early stages I had planned to use the back to back method but eventually opted to go with the damping material which of course cut the driver cost in half.