Designing a port on WinISD? Need help!

[Lurius 10+ year member]

Alright, I am building a center console/sub box and have been using Sketchup for the basic design, trying to get the design phase complete.. The box will be housing a JL 10W7, firing towards the backseat of the truck. For now I have pretty much figured the dimensions of the box itself, and once it is put together I will be fiberglassing around it to give it more of a center console "feel", as well as cupholders!

Measurements, unless otherwise noted are in inches..

The outer dimensions: 12 width x 15 height x 22 depth.

The inner diameters(using 3/4" MDF): 10.5 x 13.5 x 20.5 = 1.68 cubic feet

The driver displacement on a 10w7 is 0.09 cubic feet

so after the driver the displacement is 1.59 cubic feet

JL recomends in the manual a 1.5 cubic feet in a slot ported enclosure, and tuned to 32hz.. This is where my question comes in..

How do I design the port in WinISD? I know nothing of ports, so bear with me please! Would it be wise to tune the port to a higher hz, what effect would this have on the SQ and SPL?

-Lurius

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[Lurius 10+ year member]

Alright, I think I got the port designed right.. I'll get a picture up here in a minute of what it looks like on Sketchup..

I used WinISD beta to get the port info below, though i'd love it if someone could confirm I got all this right...

WinISD said(after getting my box dimensions and the driver's stats, etc):

With a 10.5"x1.5" rectangular port: Vent length = 19.80" - Fits perfect with about 1.5" of space left behind it..

Again, im just learning this stuff, so bear with me if im completely wrong!

I'll get a couple pics of the box up in a second...

-Lurius

 

[Lurius 10+ year member]

Pictures..Help is much appreciated!

Thanks a bunch guys!

-Lurius

 

[wesl56 10+ year member]

remember that you need to take port displacement into account... so if you want to keep it at 1.5 cubes net, then you may need to go a little bit deeper or higer, whichever you have room for

going with 1.5 cubes net @ 32hz, you will have a 10.5x1.5x24 port,

about .2 cubes of port, and .09 driver disp, aim for 1.79 gross... so ur gonna wanna go with about 23-23.5" for depth (external) (might wanna double check, but that seems about right)

 

[Lurius 10+ year member]

Anyone else check it for me please? I just want to be certain before I start building heh, would hate to waste so much MDF!

-Lurius

 

[helotaxi 5,000+ posts]

In the picture you have the opening between the inside end of the port and the back wall of the ox is smaller than the width of the port. If that is actually he case it will severely mess up the tuning and probably produce some port noise as well.

With a 1.5cf box tuned to 32hz with a 10.5X1.5" port I got 23.5 in for a port length including end correction. Assuming 3/4" material you would be looking at .31 cf for port displacement and figuring in the .09 for the sub that gives you 1.9 gross internal needed.

 

[Lurius 10+ year member]

Thanks for clearing it up for me! The width in the rear was actually wrong in the pics, I accidently added an additional 3/4" on accident, fixed it on the model lastnight but dident update the pictures.

Thanks a lot for clearing it up, just bought some new saw blades and a new saw, might but some of the larger pieces tonight(gotta try out the new saw lol!).

I will likely have to expand the size since the box isnt large enough yet, but will figure that out in a while.. Thanks again!

-Lurius

 

[Lurius 10+ year member]

Another question.. Alright, so do I calculate the box volume(1.68cf), then get dimensions for the port using winISD(10.5"x1.5" = 19.80" long for 32hz), THEN calculate the new volume? This keeps getting me right at 1.4cf before the driver displacement. Does this sound right, or am I messing up somewhere?

-Lurius

 

[helotaxi 5,000+ posts]

You can do it tht way but the way that works the best for me and gets the most predictable results is to figure the final net internal volume that I want and the tuning that I want. From there I figure out two of the max dimensions of the overall box that I can't or won't compromise on. Which dimensions these are depend on the install and the space you have to work with. I can now take the net volume, add the port displacement (including material used to build it) and driver displacement and get a gross internal volume. Convert that from cubic feet to cubic inches and divide the volume by the two dimensions that are fixed. Don't forget to account for material thickness here when figuring internal (gross internal) volume and max outer dimensions. The result will give you the internal third dimension that you need to get both the volume and the tuning that you want. It can be done the way that you are talking about but the math can get kind complex and it is likely that you will end up with a compromise design rather than the volume and tuning that you want.

 

[Lurius 10+ year member]

I'll have to give this another go, redraw the design for a little larger volume.. I was doing the displacement math wrong for the port last time, but I think I got it now!

Thanks a lot, i'll post progress pics whenver I work on it.

-Lurius

 

[Lurius 10+ year member]

heres a picture to better illustrate my question..

Does this area, just below the arrows I drew on the image get counted in final box volume, or is it included in the port?

 

[xluben 10+ year member]

you also need to add half the port width to the port length (for that type of port), and for displacement just remove what is being used as port.

EDIT: i think that has been covered, but have you been looking at air port velocity in winisd? i'd guess that it's too high //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

what's your max dimensions?

this is what i came up with, trying to work with your original dimesions:

http://www.subwoofertools.com/forum/ported-box.asp?Ew=22&Eh=15&Dia=4&Xmax=23&Vd=.09&NumW=1&Vb=1.5&Fb=32&Qts=&Vas=&Fs=&CE=0

 

[Lurius 10+ year member]

Port velocity? Im really new to this, please help me out with that. Porting is confusing lol.

-Lurius

 

[xluben 10+ year member]

http://www.carstereo.com/help/Articles.cfm?id=4

winisd will do the calculation for you (and it's more accurate) that equation only covers round ports. with a too small (or too skinny) port the air will be traveling at too high of a velocity and you'll get port noise.

 

[Lurius 10+ year member]

How would I calculate a rectangular port? Its 1.5"x 9" and its actually got a fait bit of space behind it, would it really be likely to have port noise?

-Lurius