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16th January 2005, 02:34 AM  #1 
diyAudio Member
Join Date: Feb 2004
Location: Mt. Pleasant SC

Calculating Cabinet Volume?
Ok you math wizards how would I caculate the volume on a box shaped like this? Lets' say that it's 40" tall.
Thx 
16th January 2005, 03:50 AM  #2 
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Join Date: Jun 2002
Location: USA, MN

I love the shotgun approach. How many forums did you post this question on?
If the program you drew that in ia worth anything it will give you an area, then you multiply by 40 and there's your volume. IF it doesn't give you an area, you need to break up the figure into areas you can calculate. If all else fails, make a 1" grid and start counting squares
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16th January 2005, 03:58 AM  #3 
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Join Date: Jun 2001
Location: Eugene, OR

Draw a line through the figure where the circle turns to verticle edges and consult this link:
http://mathforum.org/dr.math/faq/faq...e.segment.html to get the area of that circle section. Divide the remaining area into rectangles and right triangles and calculate their areas. Add all the areas together and multiply by 40. There's your volume. It won't be perfect because the circle section is not really a section of a perfect circle. 
16th January 2005, 04:33 AM  #4 
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Join Date: Feb 2004
Location: Mt. Pleasant SC

Thx Bill. That's what I was doing but I realized it wouldn't be perfect too. I was hoping someone had some kind of majic formula out there.
Mike 
16th January 2005, 04:52 AM  #5 
diyAudio Member
Join Date: Feb 2004
Location: Chinook Country.Alberta

calculating that shapr's area...
try this:
[(arc measure in degrees)/360]X(Pi X r^2) X 40" if I knew the measure of the arc I'd give ya the answer. stew 
16th January 2005, 05:37 AM  #6 
diyAudio Member
Join Date: Jan 2004
Location: Toronto, ON, Canada

The calculate volume, you need to find the area of that shape and multiply the area by the height.
What I see in that shape is a semicircle (top half), two rectangles (under the semicircle), and one triangle. Find the area of each and add them together. Multiply by the height. EDIT: Yikes. That isn't a perfect semicircle, it's a semiellipse. If you can somehow figure out the equation of the ellipse, you can integrate to find the area. The rest will be easy. 
16th January 2005, 05:54 AM  #7 
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Join Date: Jul 2003
Location: Doerun, GA

Your drawing doesn't quite have enough information...
See the additions to your drawing. You'll need the length of the blue line, and the distance indicated by the green arrow. The red box incorporates the straight sided section from where the ellipse meets, down to onehalf the length of the green arrow. The area of the ellipse: =1/2 x pi x 7.25 x the length of the blue line. (7.25 is half of the 14.5 inch width) Add that to the area of the red rectangle and multiply by 40" tall. BTW, how are you planning to build this? Tim 
16th January 2005, 08:52 AM  #8 
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Join Date: Jan 2005
Location: Lake In The Hills, IL

I have always found it is easist to 'break' the shape into easy to calculate shapes, find the volume (or area) for each and then add them all up. Based on your drawing, you should be able to break the shape into a triangle, rectangle, and 1/2 circle.
From there, the calculations become fairly simple. A triangle is (height x width) / 2. The rectangle is height x width. The half circle is (pi x (r squared)) / 2. After the area of each basic shape is found, then add them together. After that, multiply by the cabinet height. This is assuming that the radius of the curve is constant and not changing. Your drawing has the curve being slightly eliptical, but this may be just the drawing and I made the assumption that your cabinet would circular in that area. If not, you will need to find the formula for the area of a elipse. Hope this helps. Scott
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16th January 2005, 10:15 AM  #9 
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Join Date: Feb 2004
Location: Chinook Country.Alberta

the area...
If the "top" is in fact a semi circle then the shape's area is 93.57 sq inches or so. If it is an elipse, and a rectangle and a triangle , then just a few more steps.
What precisely is this shape in regards to its parts? stew 
16th January 2005, 01:22 PM  #10 
diyAudio Member
Join Date: Feb 2004
Location: Mt. Pleasant SC

Does anyone remember the DCM Time Windows? My wife has asked me to build a pair of speakers tha look like our old Time Windows but sound better. She just loved the way they looked because they were elegant and made nice stands for picture or statues. Here's what it looked like.

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