Originally Posted by Trendy
Well this will be a bit of a reach but perhaps it's about how much air four 7” drivers can move. Using the equation pi*r^2, four 7” drivers have a surface area of about 152 square inches.
As a rough approximation using nominal diameter which is based on frame size is OK, but the actual diaphragm size of a speaker is significantly less than the size of the frame because of the area lost to the surround. Only the inner edge of the surround moves with the cone, and the outer edge does not move at all.
For example I have here a Stereo Integrity 15", but the actual diaphragm is more like 12". A good estimate would be that the travel of the cone is uniformly distributed across the 3" surround, so about 1 1/2" of the surround is effectively moving with the cone. The diaphragm diameter is thus effectively 13 1/2 inches. We lost about 10% of the diameter or nearly 20% of the cone area.
Roughly equivalent to one 14” driver, with a surface area of about 154 square inches.
I'll take that at face value.
Individual 7” drivers will perhaps be less prone to cone breakup and distortion than a single large 14” driver.
The low pass crossover for the woofers is said to be 230 Hz, so cone breakup just isn't an issue. Breakup of 8" cones can be counted on to be higher than 1 KHz, and usually several times that.
As far as distortion goes, for woofers that depends mostly on the voice coil and magnet. In another post I just made I explain why smaller drivers are prone to lower linear limits in this important performance area.
This might provide you with a more accurate frequency response.
It looks to me like they are trying to use a column of 4 smaller drivers to allow building a more stylish, narrow enclosure. 4 drivers are more than enough to create a column array, which limits vertical dispersion while maintaining a certain amount of horizontal dispersion. Controlling vertical dispersion helps limit the mid-bass notch due to the "floor bounce". The low crossover helps avoid lobing due to multiple drivers as does the edge-to-edge placement.