Thank you for your response and passion but I must correct some of your dimensions and a basic flaw in some of your assumptions.
Okay, I'll play along. Let's see.
First and foremost, please keep in mind we are dealing with a total internal volume that is right of the decimal (less than 1).
Oh really? I guess that is not too significant. Lets look at it another way. I'll be overly generous and say your .5 cubic foot curved sides box is .4 cubic feet rather than what I stated before. That is a 20% deviation if it is less than .1 cubic feet in difference. That seems fairly significant to me.
First off, I will confess I did make an error in what I stated above. When I stated the depth of the box, I stated it as 10.125" taking into account the thickness of the brace as if half of it were gone. It should have been 10.375". That would actually make it .387 cubic feet of air space and not .377 cubic feet.
So we are at .387 cubic feet based on the posted data on your web site and taking into account some deviation in thickness near the rear of the box.
1. The cabinet walls are made using 18mm (.7087) thick MDF not 3/4” (.750). It is common when converting from metric to inches
Okay then, the internals increase to 12.6" high by 7.1" wide at the front and by 3.6" wide in the back by 10.425" deep. Thank you for that correction. You are now up to .399 cubic feet.
2. The vertical internal brace is made of 15mm (.5906) thick MDF not ¾” (.750)
Okay, that is a difference of 3mm total. I allowed for half of that thickness to actually take up air space. So I would need to give back 1.5mm to the depth. That is .05905512 inches. Now we are up to .400 cubic feet.
3. Your assumption regarding the total volume displaced by the internal brace is suspect at best. To say “subtract out the thickness of the brace minus its holes, which is ABOUT HALF OF ITS VOLUME” is not an accurate enough method of measurement..
I'll go one further than that and say that it isn't even there to begin with. That would crank it up to .414 cubic feet. We are still a long way from .5 cubic feet.
4. The walls of the cabinet do not get “thinner” toward the rear. The walls maintain the same 18mm thickness from front to rear.
Well, I measured right at 3.5" wide on the inside at the back wall. The 2" flared port from PSP is 3.97" wide on the inside and I placed it in the back of the cabinet on four of the ones that I ordered. I'd say it took out about a .25" of the side wall at the back on each side as it went through. That would also tend to confirm the 3.5" thickness on the inside. But if you insist, that makes it 3.1" on the inside. Now you are back to .377 cubic feet. That is still considering that the brace takes up half of the air space of its thickness.
5. The curve cabinet is not a “Trapezoidal” shape with the sides being straight. The sides actually bow outward before they gradually curve in toward the rear. The width of the cabinet is 8.5” at the baffle, the maximum width of the cabinet is 8.65”. This may seem minor, but again all of these “minor” issues are starting to add up!
Yep. I mentioned that. It will add a little, but not much. Deducting the entire thickness of the brace as if there was no brace there at all gives back more than that will. I'll add that back again. You are up to .380 cubic feet. We are still a long way from .5 cubic feet.
6. If you are relying on Bass Box to help calculate this may be part of the problem! The shape of this cabinet is far too complex for Bass Box to calculate correctly.
Come on now Rich. This is a simple truncated pyramid with a little curve to the sides.
Also listed below is a link to another forum from a gentleman that has read your post and measured the cabinets using simple geometry. His numbers are coming out close to ours. http://www.htguide.com/forum/showthread.php4?t=30443
That's it Rich? You found a hobbyist whose numbers came closer to yours? Come on Rich. Go measure the boxes yourself and you'll see.
Let's do this: Let's throw all this technical stuff out the window and let's say we don't know too much about math. We can only measure straight boxes. Let's just use a little common sense shall we?
These two boxes that you offer have the same size front baffle and are made to the same thickness. Right?
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=302-720http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=302-721By the numbers the one with the straight walls comes up right at .5 cubic feet, and trust me, that one is real easy to measure. You claim it to only be .494 cubic feet. Great! That is plenty close enough.
Your engineers at the factory that happens to be "one of the best cabinet factories in the world" states that the difference in internal volume between the two boxes is only .017 cubic feet.
The curved one is .5" deeper (which would add .018 cubic feet on the curved box over the straight one, by the way), however the rear baffle gets 4" smaller on the inside compared to the front baffle (7.1" to 3.1") and is a significant difference.
And it only lost .017 total cubic feet? Really? REALLY?
It lost 4" on the back wall over a 12.5" tall area and only lost .017 cubic feet?
That would be the same as taking the straight sides box that is .5 cubic feet and shortening the depth by .335". So shortening the depth of that box by .335" (that is less than 3/8 of an inch) gives you the same air space as adding .5" of depth and reducing the rear wall width by 4"? Are you kidding me?
If you took the box with the straight sides and moved one side wall in by .25" it would reduce the internal volume by .018 cubic feet.
Come on! I am really trying to help you out here.
Our factory is one of the best cabinet factories in the world. They have over 30 design engineers on staff using the latest CAD systems that can accurately calculate internal volume and we stand by our measurements.
Considering how well these front baffles fit on the rest of the box (or didn't fit), and the variance in the amount of overhang around the sides, I have a tough time going along with the "best cabinet factory in the world".
What I do think is that these are pretty nice cabinets and very nice for the money. I like them well enough to recommend them (with a minor modification) to my customers to use in 4 different kits that I offer. I am driving sales your way. Nice boxes, but the published air space value is not correct. ALL of the published air spaces on ALL of your curved boxes are not correct.
So, how about taking some measurements on those boxes yourself and getting back to us?