Another Bandpass, but WINISD related, Thread

[Bakerman]

Lets start with my available dimension.  Im building for the back of a Jeep Cherokee.  My width is set at a 39" max.  Height isn't a hard stop, but I would like to keep it under 17".  No restrictions on depth that anyone would get close to designing anything like this.  The driver is a Skar ZVX-8

 

So to the point, I'm not asking for someone to design a box, but just incase anyone asks, I went ahead and got details covered.  Ive been wanting to try out my skills at a 4th order.  My main two resources are Steves old write up on the topic, about a 2:1 ratio, manufacturer specs on the sealed, twice the area for the port, tune high, etc.  So I designed a box that is 12*12*12 for the sealed.  With displacement, it comes out to a net volume of .67 c/ft and the manufacturer recommends .65c/ft.  So I feel like Im golden on that.  The ported section is 24.5" wide, but the same 12" tall and 12" depth.  The port measures 10.5" (box height minus wood thickness) and 2.85" wide with a length of 6.90".  (I know the decimals are hard to actually get on a table saw, but its the math, work with me)  This gives me a ported section with a net of 1.35c/ft, 14.45sqin of port area, and a tuning of approximately 50hz.  Now when I go to put this in WINISD, not only is my peak at like -5db, but the low is 11hz and the high is somewhere in the 100'shz range.

 

Then I found this super complicated set of math forumula's that suppossed to give you the perfect dimensions based off the specs of the driver.  You can find the writeup at this link.  Anyways, by the time I do all the math, with an S value of .7 at 3db peak, it gives me similar specs.  I get a sealed portion of .60c/ft net and a ported section with 1.5c/ft net and a tuning of 47hz.  This seems more "exact" than SMD's formula, so why not go with this?  Well, when I plug it in to WINISD i get similar plot points as expected.

 

So at the end of the day, should I go with my gut and build it out to specs similar to above, or am I doing this all wrong and have no concept of what I am doing?  My goal is to have a daily driver with a loud setup, but is clean and can actually be listened too.  So i thought if I can design a box with a good flat response across the spectrum of about 40hz-100hz I would be good.  But this is turning to be a bit complicated.  Pic for attention, just to show you I actually do this math by hand.  Im a bit old school

[Joe X]

Checked the t/s parameters for that sub and the parameters don't match, this is typical for skar audio and the only way to get the true parameters is to break in the sub and then measure the parameters yourself. And then with that information decide which box should be built for it.

 

Secondly WinISD is designed for home audio and cannot directly simulate a cars cabin gain, you need a workaround to very coarsely simulate frequency response:

 

 

internal car length = l [m]

speed of sound = c [m/s]

 

Setup the following filter :Linkwitz transform:

 

With the following parameters:

f0 = c / 2l  (solve this formula)
fp =15
Q0 =0.707
Qp =0.707

 

Be aware that when the filter is on the rest of the plots are invalid.

 

Sorry this had to be that difficult but it cannot be made simpler.