CBT 36 Circular Arc Line Array Loudspeaker
Designer: Don Keele Marshall Kay
Project Time: 20+ hours
Project Complexity: Professional
Project Cost: Over $1000
The CBT36 is a special design called a “CBT circular-arc ground-plane line array.” The CBT36 contains 18 each 3-1/2” full-range drivers used as mid woofers, and 72 each 0.72” diameter tweeters mounted on a 36 deg circular-arc front panel. The system stands about five feet tall with a width of about 6-1/2 inches, and a depth at the base of about 23 inches.
The system has extremely well-behaved and smooth coverage from locations well above the array to points even down at floor level, and at distances from directly in front of the speaker to points in the rear of the listening room. The horizontal coverage is extremely broad and uniform even out to plus-minus 90 degrees. The CBT36’s variation of loudness with, distance is also very unique. At standing height, the system’s volume level hardly changes over a range from directly in front of the system to points 10 feet away! The CBT36 has been specifically designed to operate over a reflective ground plane, which is a fancy name for the floor, and does not suffer from destructive floor-bounce effects. The curved line array of 72 tweeters extends all the way down to the floor to take advantage of the ground-plane acoustic reflection. Effectively the floor provides a reflective surface that acoustically extends the array below floor level and thus creates an array that is over 10 feet tall and controls vertical coverage and directivity down to below 160 Hz!
An active DSP crossover divides the spectrum into multiple parts, the bass-mid drivers operate from 50Hz to 1KHz and the tweeters work from 1KHz up. In addition to dividing the spectrum, the crossover also provides parametric EQ to compensate for diaphragm resonances. The crossover pictured above is a cost effective solution but you can choose other options if you prefer, however you should contact us before purchasing a different DSP crossover so we can verify that it has the necessary functions to work optimally with CBT36. The crossover chosen here was the Behringer DCX2496 ULTRADRIVE PRO DSP Crossover.
To achieve a high end finish you will need to sand and prime the parts. We recommend that you start with 150 grit sand paper to sand the edges, this will remove remaining tool marks. Next move to 180 grit and continue sanding the edges and finally use the 220 grit sand paper. Apply a heavy solids primer compatible with the paint system you have chosen, if you spray the primer on, you will need to consult the paint vendor for recommendations on tip diameter and air pressures. Allow the primer to cure for the specified time prior to sanding. Start with 220 grit and sand all surfaces lightly, but pay particular attention to the edges. Step up to 320 grit paper and again sand all surfaces lightly and finally move to 400 grit and again sand all surfaces. If you wish you can continue to 600 grit sand paper as the last sanding step.
The CBT36’s variation of loudness with distance is also very unique. At standing height, the system’s volume level hardly changes over a range from directly in front of the system to points 10 feet away! In other words, if you were to set a loud listening level at a typical listening distance of 10 feet and then walk towards the system, the speaker’s volume will not get any louder even though you walk up and stand directly in front of the speaker! This one has to be experienced to be believed!
About The Designer
Marshall Kay and Don Keele of Audio Artistry brought their concept to reality in conjunction with electronics supplier Parts Express and its Dayton Audio brand of loudspeaker components to create the CBT36, the world’s first broadband constant directivity (CD) loudspeaker system for the home. The CBT36 system provides extremely even coverage and flat frequency response at all locations in the listening room.
Project Parts List
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