Originally Posted by chalugadp
I finished my Marty sub sketchup ..
Wow, Chalugadp. I really like your sketchup model. I have a few thoughts about the bracing I thought I would share, partly because I felt a need to explain the pseudo-engineering concepts I was using for my bracing.
1. Deeper braces are better than shallow braces for making panels stiffer. Bracing stiffness increases as a function of depth squared (^2), eg. doubling the brace depth from 1" to 2" results in a brace 4 times as stiff.
2. If the Slot Panel has lengthwise braces on one side, minimal stiffness is added by additional lengthwise braces on the opposite side. Cross braces on one side and lengthwise braces on the other side will behave the same as if the braces were both on the same side. That is why the top of my Slot Panel only has cross braces, because I felt additional lengthwise braces would be redundant. Granted, they are not as deep, and therefore not as stiff as the added lengthwise bracing, but I felt the added complexity could be avoided with minimal impact on structural stiffness, especially since the shorter slot braces are supported by a panel on BOTH sides.
3. Regular wood is stiffer than MDF, but is also more likely to resonate. I felt that the relatively short pieces of natural wood would offer superior strength to weight ratios vs. MDF and yet would still be sufficiently stiff as to not resonate within the operating range of the sub. I have no proof for this last assertion.
4. Large area lap joints are easy to construct and offer superior bond strength compared to but joints, even if biscuits are used. Furthermore, I built the lap joints with one piece intentionally short to minimize the number of precision cuts required and potential rework if the length was too short or too long. I really like the look of many of the window braces I see in the build threads, but I think many of them fall short in terms of either the lack of stiffness they add to the design or the added weight without substantially increased strength. Lastly, some of those window braces are very complex and look like they require a lot of time and precision for a good fit.
Given the above, I would suggest the following changes to your design:
1.Extend the Slot Braces all the way to the back panel. You can make them taller beyond the inner port opening if you wish.
2. Eliminate the redundant longitudinal Slot braces on top of the Slot Panel and add cross braces instead.
3. Add full cross braces to the rear panel. There is no need for the bracing here to resemble the front panel, because you don't have to worry about clearance around the driver.
4. I like the double bracing that you have drawn, and it may be necessary, I don't know, but it will definitely make the building that much more challenging and time consuming.
Please don't take these suggestions as being too critical. I really like your design, overall, but from my limited experience, the bracing looks like it will be a tough build. Now, if you figure a clever way to build the bracing on the bench and place the majority of it into the sub already assembled, you will really be on to something!!
Awesome skethchup model! You are definitely THE SKETCHUP MAN!