Ported box for a MMATS Dread 12

I am building a box for a friend but have no experience with ported boxes. As far as I know they have to be built pretty much dead on to spec or the sound will suck. Here ar the specs for the sub: (its the dread 12)
https://www.mmatsproaudio.com/pdfs/Recommended%20Enclosures%202004.pdf
I got the 2cf but the 25sq"x16"L and .25cf displacment for the port are new to me. If anyone could help me with this I would appreciate it, thanks in advance!

The 2 cubed feet is NET meaning without the volume of the woofer and port added...so the box should be built around 2.7 cubed feet...leaving some room for bracing.

With that port the tuning is about 38Hz

Use this https://www.carstereo.com/help/Articles.cfm?id=31 to help you with the tuning and how to tune the box

"25 square inch by 16 inch long" refers to the volume of the port.  If the port is inside the enclosure, as it usually is, the port volume infringes on the box volume just as much as does the drivers themselves and the added bracing.  The displacement of all these objects must be added up, added together, and subtracted from the gross box volume.  This will give you the new net box volume.  It is this final net volume that you use to determine tuning frequency.

Multiply three dimensions to find the cubic answer.  In inches, feet, meters or whatever you are working with.  The link in the answer above has calculators that will change from one unit to another unit. 

Now, look at the 25" sq X 16" problem:  that is akin to a slotted port design, or it could likely refer to a roughly 6" round port.  This site has some good, friendly calculators as well, and you can figure this one out using one of those.  Go to https://www.the12volt.com/caraudio/boxcalcs.asp

Scroll down to Volume calculator - Rectangular or square.  Now you have to find two numbers that when multiplied equal 25", because the problem gives you the number as "squared".  Do this by dividing 25 by 2, which equals 12.5.  Now you have the three dimensions you need:  12.5, 2, and 16.  Input those numbers in the calculator.  Enter "0" in thickness, as we will assume these dimensions take the port wall thickness into account already (but you will need to research that).  You will get your answer in cubic inches.

There are 1728 cubic inches in one cubic foot (12 x 12 x 12).  After you have found all the displacements in cu inches, divide by 1728 to convert the sum to cubic feet.  (The ".25cf" you mentioned above refers to a rough, but close enough, port displacement in cubic feet.)

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Ok I pluged those numbers in and came up with .231 the port displacment was set at .25 is this going to play with the sound of the sub at all being off by about .02? Sorry about the questions I just want to get this thing right.

So overall the space inside the box with the port should be damn close to 3888ci? Take the 3456 (2cf for the sub) and 432ci for the port and divide by 1728 to get an overall of 2.25cf.

Here is a box I drew up just to see if this is right. The orange area is the 2cf for the sub and the grey is the .25 for the port and is 16" long, did I get it?

.25 is a rounded-off number in the spec sheet.  Use your figures, and be sure to include the entire port structure including its walls.

When you are deriving box airspace, use only the airspace that is dedicated to the woofer, not the entire amount that includes ports and baffles.  Saying that it is 2.25 overall can cause confusion...if there is exactly 2 cu ft dedicated to the woofer then that is what you would say.  It would be a 2 cu ft box.

...and don't ever be sorry about asking questions.  That's what makes this forum go 'round. 

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

So as long as I have a 25sq" port that is 16" long be it round or sloted I am good? Did you see the box I drew up? Would that be the correct way to measure the port and the displacement for the sub?

Thanks again for all your help! Just kinda sucks that stereo stuff isnt my strong point so I am learning new stuff everyday!

Isn't "net" volume total volume and "gross" the total without extras added in...But hell I am really now sure...I always get confused between net and gross measurements

Gross is the whole thing.  Net is the airspace that's left for the woofer after displacements have been deducted.  You can be reminded of this every time you pick up a jar of something from the grocery store...it will say on the label "nt wt" or "net weight", which will indicate the weight of the product in the jar...but not the jar itself.

otto34, the drawing doesn't indicate how to measure.  But you are definitely on the right track, and this type of knowledge doesn't come quickly.  The drawing indicates, to me, that you are a pretty good drawer but not yet a box designer.  Arrange the port so that it fires out the same side as the woofer, even if you have to put an elbow in it.  If you want to invert the woofer as the pic illustrates, allow an additional approx. .03 cu ft for the area within the cone, which will be a part of the box volume.

I make much cruder illustrations, and here is an old one to prove it.  This shows that an inverted cone driver will add to the airspace in the box:

There is always a little bit of guesswork involved in coming up with net airspace, and the ".25" in the spec sheet that we talked about proves the point that it is alright to be close.

For your port displacement, measure the port structure from the inside of the baffle to the end of the port, in length.  A 16" port that is mounted through a 3/4" baffle will actually measure 15 1/4" long.  Find the outer diameter, not the inner, for port structure measurement.  A 4" inside diameter might measure 4.25" on the outside.  This total volume is displacing air from the enclosure.

Oh, I just double-checked your question and, yes, round or slotted doesn't matter as long as the square inch opening is 25".  That's inside opening area.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Damn, Steve, those autocad drawings are freakin awesome....look drawn to scale to me lol

Just messing

So then this looks better?

Well I think I am kind of getting it. I just wanted to know if you run an elbow in your port do you measure from the center of the port to get your 16" of port lenght?

nouseforaname wrote:

---

yes, use the center line of the port from one end to the other, even through the elbow.

---

Cool deal, thanks bro!