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need help building a ported box for my 2010 single cab f150


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i just got a pair of sundown sa-10. i know they reccomend a ported or sealed enclosure. i would like to go with a ported since i have a planet audio 2600w amp thats going to push them. i just dont know how or understand how to figure the dimensions for the ported box. i have a total space of 48"w X 12"d X 12"h. it says i need a 1.0-1.25 cubic feet tuned to 35Hz. any pics or cut out lists would be a big help. i also plan on using 3/4 MDF.

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Here's how to figure volume (air space) in a box:

You have 48x12x12 gross area but assuming you'll be using 3/4" mdf, you only actually have 46.5x10.5x10.5 of volume. To find out how much that is, you need to multiply the three numbers and that total is 5126.625inⁿ. To convert that number to cubic feet, divide 5126.625 by 1728 (one cubic foot), for a volume of 2.97ftⁿ.

So, you have almost 3 cubic feet in which to put two subs that want 1-1.25 cubes each. I'll assume that your most important two dimensions are the height and depth, so we need to find the width that will make the box the size you need. First, let's assume you want the box to be 2 cubes net (1 cube each) and let's use Sundown's recommended 35 Hz tuning.

For net box volume, you have to account for the space the driver(s) & port(s) displace, so that total has to be added to our 2.0 number. The SA-10s displace .1ftⁿ so add .2 to 2.0 for 2.2. Next, use a port calculator to find the volume of the ports. We'll use two four inch ports and this calculator. Using that calculator, we find that we need two 4" ports 24.72" long. We can assume 24.75 for ease of measuring with a fractional tape. To find the volume the ports will displace, we need to measure the Sd of the outside dimension of the port.

A 4" schedule 40 PVC pipe is ~4.5" in diameter so using the PiR² formula, we take half the diameter (2.25) and multiply it by itself and then Pi: 2.25x2.25x3.14159 = 15.9in². Then we take that measurement and multiply it by the vent length of 24.75 for a total of 393.52inⁿ Since we have two ports, double that number and add it to the 2.2 we have so far.... 393.52x2=787.04. Then divide 787.04 by 1728 for a total of .45ftⁿ and add that to 2.2 for a total of 2.65ftⁿ.

So now we know we need 2.65ftⁿ of gross volume in the box in order to have a 2ftⁿ box tuned to 35 Hz. Going back to square inches, we multiply 2.65 by 1728 for a total of 4579.5inⁿ. Then, to find the width we need for the box we divide 4579.2 by 10.5 by 10.5 or, 4579.2/10.5/10.5= 41.53. So that's the inside measurement of the box. The outside would be 43, since we can round the .53 down to an even .5

The next dilemma we have is where to locate 48" of port in a 43" space. We can't have one port on each end, because they're too long and we don't want to offset them so, we'll put both on one side (let's say the right) and then we'll shift the woofers both to the right so that they don't fire directly into the port openings.

And to note... offsetting the ports isn't a really bad thing to do but given their lengths, they would wind up being really close together inside the box and doing that would cause an excessive amount of cross flowing turbulence which would lead to an excessive amount of port noise in an otherwise good sounding box. So that's why I said we don't want to offset them... in this instance.

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Well then, slot port volume is calculated just like any other square volume, so it shouldn't be a problem to figure out with the information above. Just remember to use the outside dimension of the port when calculating displacement and use the inside dimension when tuning. ONe slot port with the same area as two 4" ports will be 2.25x10.5.

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all the math makes my head spin.. it gets a little over whelming when you dont understand it.. do you have a shop in shreveport? i stay in texarkana is why i ask

I sure do. And, I can help you out... just send me a PM.

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