In Reply to: RE: "The use of two 12" drivers gives you the cone area of a 24" woofer " posted by b.l.zeebub on July 10, 2013 at 06:40:41:
I believe there is still substantial confusion here about Sd. The nominal diameter of a driver typically includes the surround. Normally only about one-half of the surround is part of the sonically emissive diameter of the driver so adjustments need to be made for that. Also some drivers such as my AER MD-3s have no central dust cap so a circular area at the center of the cone must also be subtracted from the effective area of the cone to compensate for this. To complicate things further some manufacturers measure the maximum diameter of the driver including basket area completely outside the cone to state the diameter of the driver while others are more conservative and only state the diameter of the cone as the size of the driver. These sorts of things are why one should always measure drivers for themselves before designing enclosures for them unless the manufacturer provides very comprehensive specifications and is totally trustworthy.
All that being said for at least forty years I have guesstimated the effective cone area of a driver by first calculating the radius as being 85% of the nominal radius of the cone. This is to compensate for the above listed non sound emitting parts. Then just calculate the area of the circle with Area = Pi X radius squared. As an example a 12" driver has an effective radius of 12 X 85% divided by 2 = the effective radius. 12 X .85 / 2 = 5.1". 3.14159 X 5.1 X 5.1= 81.71 square inches. With these simple steps you can arrive at a good estimate of the sound emitting area of the driver.
I do not believe the depth or slope of the sides of the cone need be considered.
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Follow Ups
- RE: "The use of two 12" drivers gives you the cone area of a 24" woofer " - Don Reid 07/12/1314:55:23 07/12/13 (0)