Box Build for two Skar VVX 12"s

[Sheena]

Equipment: 2 Skar VVX 12" & BRZ1200.1 in a 9th gen civic.

Well i know it took longer than a week, but its been rather humid here in Houston so.

We finally went and got the MDF at Home Depot Tuesday and we will start cutting it up Friday morning.

The final box specs are..............:

I had a question about the port area, honestly it seems small to me and its been bothering me. i know its 12-15 sq in per cube, but i rather ask here than go and cut the wood and not be happy.

The current box i have in there now is 3.78 cubes @ 32hz with 10.99 sq in of port per cube. so jumping to almost 13 sq in will be a HUGE upgrade imo. but i'm no expert.

also these are the absolute max dimensions that can go into my car, i project that i'll have to remove the trunk lid already.

[Joe X]

Consider this one:

Enclosure Specifications:

Fb = 31 Hz

Vb = 3,7 ft^3

External Height = 15,5 in

External Width = 37,01 in

External Depth = 20,25 in

Port Width = 4 in

Cut List:

* All Dimensions in Inches.

* Wood Thickness is 3/4 for all Parts.

External Enclosure Parts:

Front = 32 1/4 x 14

Back = 37 x 14

Left & Right Sides:

Side 1 = 19 1/2 x 14

Side 2 = 18 3/4 x 14

Top & Bottom = 37 x 20 1/4

L Port Internal Assembly Parts:

Front to Back = 14 3/4 x 14

Extension = 14 x 14

The .05 cuft brace you considered is accounted for.

[Sheena]

i appreciate you taking time to look at my situation, but i have a few issues lol.

firstly, what calc did you use to get those numbers? i assume thats without the sub displacement, which is .36 cu ft which would drop my cu ft down to 3.4

that would be cool, cause i'd have a 15.64 sq in port per cu ft, but not enough net cu ft for the subs.

i suggest going and looking at Torres calc, which every member uses here.

http://www.stevemeadedesigns.com/board/topic/38791-torres-box-tuning-calculator/

im not bashing or hating you etc, thanks for the input, but after overviewing a 4" port it leaves me with 3.46 cu ft net for the subs. i was thinking MAYBE 3.75" but that leaves me with 31 hz tuning.

the goal is around 3.8 net and 30hz tuning with the proper amount of port.. whats the proper amount of port for my situation?

[Sheena]

So i woke up and this is what i found...

No worries, after a phone call i found out that he was getting it inspected for me!

onto some tease pics.

Ah, much better!

[Joe X]

I recommend to do all caclulations manually if you want to make sure and you have the time. All calculators only use this for figuring out the tuning of the box:

Fb = 0.159*sqr(Av*1.84e8/(Vb*(Lv + 0.823*sqr(Av))))

Lv = inches, Av = square inches, Vb = cubic inches.

Vb is net internal airspace before displacements. Above I considered 0.05(brace) + 0.36(both subs) + port (airspace + wood) displacements.

And nevermind this was just a suggestion.. I just figured that you would need a golden ear to notice a 0.07 cuft and 1 Hz difference.

[Sheena]

im not sure what the calculations are on this type of box.. but did you take them into account?

this will be the type of box that will be built, because a typical slot port (3 common walls) with a 33" long port creates some nice loading issues. (correct me if im wrong)

[Joe X]

If you calculate the box on the pic you will find that you run out on depth by far (with that 20.25 external depth) if you want to have any decent port area on that tuning (Fb).

[Joe X]

Ok so here's all I can do, 2 different designs, the second one goes above width by 7/8 but you gain flush mounting:

------------------------------------------------------

Enclosure Specifications:

Fb = 30 Hz

Vb = 3,8 ft^3

Subwoofer Mounting = Front Mounted

External Height = 15,5 in

External Width = 37,04 in

External Depth = 20,25 in

Port Width = 3 3/4 in

Cut List:

* All Dimensions in Inches.

* Wood Thickness is 3/4 for all Parts.

External Enclosure Parts:

Front & Back = 37 1/16 x 15 1/2

Left & Right Sides = 18 3/4 x 14

Top & Bottom = 37 1/16 x 18 3/4

L Port Internal Assembly Parts:

Front to Back = 15 x 14

Extension = 13 1/4 x 14

------------------------------------------------------

Enclosure Specifications:

Fb = 30 Hz

Vb = 3,78 ft^3

Subwoofer Mounting = Flush Mounted

External Height = 15,5 in

External Width = 37,88 in

External Depth = 20,25 in

Port Width = 3 5/8 in

Cut List:

* All Dimensions in Inches.

* Wood Thickness is 3/4 for all Parts.

External Enclosure Parts:

Front = 33 1/2 x 14

Front Internal = 32 3/4 x 14

Back = 37 7/8 x 14

Left & Right Sides:

Side 1 = 18 3/4 x 14

Side 2 = 18 x 14

Top & Bottom = 37 7/8 x 20 1/4

L Port Internal Assembly Parts:

Front to Back = 15 1/8 x 14

Extension = 12 1/4 x 14

------------------------------------------------------

My take, trust no calculator (or my calculations for that matter) do your own math so that you can trust what you are building.

[Sheena]

im liking how the second one looks, but instead of 3 5/8" port, ill be using the port from the first one, 3 3/4"

leaves me with 3.77 cu ft net and 30hz... with..... 13.93 sq in of port!

after the holidays i have to make a mock up with cardboard and see if i can fit the extra 7/8" of width into the car.

im thinking i might be able to.

thanks for the calculations Joe, i hope you took nothing i said as offensive. your feedback lead to what i was looking for.. more port area if needed.

from 10.99 to 13.93.. i think my subs will love me for more port

[Joe X]

Here you can read all about the topic:

http://www.jlaudio.com/header/Support/Tutorials/Enclosure+Ports/Tutorial%3A+Enclosure+Ports/656168

Here are some online tools that you may find useful:

http://www.the12volt.com/caraudio/boxcalcs.asp#porsq

I have found no flaws with the above tools.