[fredm]

I am planning on making another box but this one with dimensions of 22x22x50 or so kinda a bigger version of this box

The box pictured has no braces and is really solid because of the rectangular shape. This larger box though I was thinking of putting in 2 internal braces parallel to the plane of the side the ports are on, kinda evenly spaced in the box.

You guys think that is enough?

 

[Aaron Gilbert]

What makes you think a rectangular shaped box is any more strong than another shape? :scratch:

Adding a couple braces as you describe is a very good idea. At 50" on the long dimension though, I'd probably add at least two more braces.

 

[fredm]

What makes you think a rectangular shaped box is any more strong than another shape? :scratch:

Adding a couple braces as you describe is a very good idea. At 50" on the long dimension though, I'd probably add at least two more braces.

when you have a cube you have much larger areas of both directions quite far away from a "wall" and higher chances for resonance. Plus for a given cubic foot sized box the more material you use to make it the better and a rectangular has much more surface area of MDF than does a cube or other design.


I am not doing it on purpose for this reason, it just needs to be this shape to fit.

 

[Aaron Gilbert]

when you have a cube you have much larger areas of both directions quite far away from a "wall" and higher chances for resonance. Plus for a given cubic foot sized box the more material you use to make it the better and a rectangular has much more surface area of MDF than does a cube or other design.


I am not doing it on purpose for this reason, it just needs to be this shape to fit.

There's nothing wrong with the shape being made to fit where you want. And I wasn't implying that a rectangle is worse than a square - a cube is made up of rectanges by the way, just with all sides the same length. I was implying that other shapes such as a cylinder/tube are much stronger than a rectangular enclosure and often don't need bracing. With a cube vs. an elongated rectangular box, yes, the total span in one direction will be longer than the rectangle for a given interior volume. However, the span in the other direction will be smaller. For a given surface area, a square cannot have a longer span in both directions than an elongated rectangle.

More material isn't necessarily better, for a given size enclosure. A substantially stronger and less resonant box can be made using only 3/4" thick walls and lots of lightweight bracing, vs. an enclosure with 1.5" walls and limited bracing.

 

[fredm]

More material isn't necessarily better, for a given size enclosure. A substantially stronger and less resonant box can be made using only 3/4" thick walls and lots of lightweight bracing, vs. an enclosure with 1.5" walls and limited bracing.

obviously I meant similar bracing or lack thereof.

So you think the 2 panels will be enough for that size box? This is by far the largest box I have ever built and the first to use real bracing.

 

[Aaron Gilbert]

obviously I meant similar bracing or lack thereof.

So you think the 2 panels will be enough for that size box? This is by far the largest box I have ever built and the first to use real bracing.

Are all walls 3/4" material? If so, I'd say you probably want at least three braces along the 55" dimension. With two braces, you still have unsupported lengths of at least 18". Go to three braces, and that drops to just under 14". I'd use four braces myself, that gets your span down to 11". My box has 48" wide panels, and I used four braces across that width - though two additional near the center.

If your walls are 1" or thicker, you might be able to get away with two braces. Also playing a factor will be the strength and excursion of the woofer.

All that said, I don't know if there are any hard and fast rules for bracing. I don't recall reading such in any of the usually referenced loudspeaker design literature. Most DIYers tend to err on the side of overbuilding, rather than underbuilding. Most people tend to make braces from the same material as the enclosure, ie 3/4" MDF, which they join to all four sides of the cabinet, then cut a big circular hole for air passage. There's nothing wrong with this method, except that it adds significant weight (could be a benefit depending on your point of view) and takes a lot of extra material, most of which will be cut out into big MDF discs and removed. I prefer to use dimensional lumber (2x4) for bracing, unless I just happen to be making a divided cabinet where I want to seal off one side from the other. 2x4s are easy to add at any time even after the box is full constructed (but before veneer or paint are applied). Other people are fans of bracing with wooden dowels of 3/4" to 1.5" thickness, and that can also work well.

 

[fredm]

Are all walls 3/4" material? If so, I'd say you probably want at least three braces along the 55" dimension. With two braces, you still have unsupported lengths of at least 18". Go to three braces, and that drops to just under 14". I'd use four braces myself, that gets your span down to 11". My box has 48" wide panels, and I used four braces across that width - though two additional near the center.

.

The length is 50" and unless I am wrong it should be 12"X22" of "unbraced" wall.

Also when bracing a 22x22x50 would I want a brace with one large hole or say 4 small holes? I mostly see one large hole which would seem only to really excel in adding weight to the panel walls, is this the function of bracing, or am I looking to mostly add structural integrity (where is seems 4 smaller holes would excel giving it a center cross shape)?

 

[Aaron Gilbert]

The length is 50" and unless I am wrong it should be 12"X22" of "unbraced" wall.

Also when bracing a 22x22x50 would I want a brace with one large hole or say 4 small holes? I mostly see one large hole which would seem only to really excel in adding weight to the panel walls, is this the function of bracing, or am I looking to mostly add structural integrity (where is seems 4 smaller holes would excel giving it a center cross shape)?

My bad, I had 55" in my head for some reason. I'm not sure how you are getting a 22" x 12" span with only three braces along the 50" dimension, though? Even if those are external dimensions and you're using 1.5" thick walls, that's 45.5"/3 = 15.17". Then again, that's still considerably smaller than your 22" dimension, so if the 22" is ok, you should be fine with that also.

I can't answer your questions about the single large hole vs multiple smaller holes. My instinct is that either will work fine. After all, many commercial subwoofer bracing consists of nothing more than a 1x2 piece of MDF or plywood joining the two largest panels together, sometimes joined with another piece perpendicular. Any brace joining all four sides together is going to be far stronger than that.

 

[fredm]

My bad, I had 55" in my head for some reason. I'm not sure how you are getting a 22" x 12" span with only three braces along the 50" dimension, though? Even if those are external dimensions and you're using 1.5" thick walls, that's 45.5"/3 = 15.17".

yeah I confused myself LOL!