How to get the right volume in a trapezoid box? - Page 3 - diyAudio
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Old 12th March 2013, 10:49 PM   #21
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The position of the trapezoids would not matter as long as they are parallel to each other. Now truncate one at an angle and thing would change, but otherwise rotation about the axis will not change the math for a simple trapezoid at each end.
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Old 12th March 2013, 10:52 PM   #22
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I'm sure the missing height can be calculated from the dimensions given. That doesn't excuse the lack of disclosure in the OP. No, I'm not ragging on the poster; he's probably just frustrated. Math'll do that to ya.
I would've just calculated the rectangle and subtracted the triangles.
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Old 12th March 2013, 11:05 PM   #23
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I now understand what Dave was saying. When I looked at the dimensions of the top and bottom, I admit to misreading. [read: egg on face]. In my mind this was a trapezoidal prism, aka a pyramid with the top cut off.

Man, you have to be careful, this coulda turned ugly with me ending up at the bottom of the pile.

Hey natural sound, give us a sketch or something next time would ya? Ol' Cal was wondering what others were thinking when they were doin' the same at me. I couldn't understand X's math even though I know he's good. When Dave stepped in I had to take a step back as his first comment was WTF? [to me that is]
So, I go pick up my wife from the train, come back, read the first post again and let out a big sigh.

Am I still allowed in this thread?
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Old 12th March 2013, 11:22 PM   #24
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Fill it with sand, pour the sand into a measuring jug?

Just by way of a second string?
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Old 12th March 2013, 11:23 PM   #25
Decker is offline Decker  United States
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Fill it with water and then pour the water into a measuring cup.
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Old 12th March 2013, 11:31 PM   #26
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The volume in cubic inches (to keep unit homogeneity) is:
(9+6)/2 in x (7+4)/2 in x (height) in =
7.5" x 5.5" x H"= V cu in

being:
in = " = inch
H = height in inches
V= volume in cubic inches.
Divide V by 1728 to get cubic feet.

By the way: that looks like a pretty small box, definitely narrow and thin, what speaker will live in it?

EDIT: Carl, I also see it as a truncated pyramid, only base is not square or rectangular but a trapezoid.
So we have to compensate on 2 out of 3 dimensions.
Hope now the OP does not add: "oh, I forgot, top and bottom are not parallel"

Last edited by JMFahey; 12th March 2013 at 11:34 PM.
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Old 12th March 2013, 11:54 PM   #27
xrk971 is offline xrk971  United States
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I am re-reading the OP post 1 and see a completely different geometry now: 9x7 rectangle bottom and 4x6 rectangle on top wall. Still don't have height. But if height is 12 for sake of assumption, volume is now average of top area 4x6 and bottom area 9x7 times height which is assumed to be 12 or (24/2+63/2)x12=522 cubic inches. A picture IS worth a thousand words in this case!
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Old 13th March 2013, 12:26 AM   #28
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Quote:
Originally Posted by Cal Weldon View Post
I now understand what Dave was saying. When I looked at the dimensions of the top and bottom, I admit to misreading. [read: egg on face]. In my mind this was a trapezoidal prism, aka a pyramid with the top cut off.

Man, you have to be careful, this coulda turned ugly with me ending up at the bottom of the pile.

Hey natural sound, give us a sketch or something next time would ya? Ol' Cal was wondering what others were thinking when they were doin' the same at me. I couldn't understand X's math even though I know he's good. When Dave stepped in I had to take a step back as his first comment was WTF? [to me that is]
So, I go pick up my wife from the train, come back, read the first post again and let out a big sigh.

Am I still allowed in this thread?

Yes all is welcome on my post no matter what cal . This is the height of the box all the way around. The box is 40 inchs tall. The front and back's are the same which is the bottom is 11 inchs wide and the top is 6 inchs wide. The sides are 10 inchs on the bottom wide by 2 inchs on the top wide. Now I used 3/4's birch ply-wood. The box was cut wrong and the guy who was helping me was in a hurry and was not listening to me. Cost me a lot of money and time so he got fired. I had to finsh Cutting angle cuts on a broken table and with a circle saw is not fun for a first time user. Jeff

Last edited by cross reference; 13th March 2013 at 12:40 AM.
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Old 13th March 2013, 12:57 AM   #29
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Okay here are some pictures of the boxes I have been working on and testing a drivers the Fostex Fe 126en drivers sounded very natural and modd by me in the blue boxes. Then I re-did the boxes in black stain with the Fostex FF 125WK drivers and they turned out very, very nice sounding . I cut a hole for a driver I thought I was going to use but, I messed up. I will start from the ground up and redesign my boxes. This is why I wanted to figure out how to get the right cubic feet in a trapeziod. Jeff
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Old 13th March 2013, 12:58 AM   #30
Dave R is offline Dave R  United States
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Quote:
Originally Posted by Decker View Post
Fill it with water and then pour the water into a measuring cup.
line with a plastic bag first. This works.
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