4th order in crown vic (now ported)*(back to 4th lol)*

[dsw422]

thanks. so I calculated wrong on the port area. according to carstereo.com ill need a minimum area of 354.95.. does that sound crazy or is it just me?

also.. I downloaded the WinISD alpha (the better version). and my graph changed (slightly)

[dsw422]

so I drew up the box in sketchup just so yall get an idea of how itll look..

[Triticum Agricolam]

You want to get the newest version of WinISD, you can get it here: http://www.linearteam.org/download/winisd-07x.exe

Like JoeX said, WinISD doesn't adjust the output based on the port size. You need to do that yourself. Enter in how much power you are going to be running in the "Signal" tab and then take a look at the "Front port - air velocity" graph. For bandpass boxes I'd suggest keeping it under 20 m/sec if you can.

[dsw422]

thanks triticum.. that's the one I downloaded to get the second graph.

so I did what you said.. with same net box size and tuning, the minimum port area to be below 20m/sec is 270 sq in... that's huge for just 2 15s..

anyway.. quick question about WinISD, what is the difference between front and rear port velocity.. I ask this cuz the 4th order only shows velocity in front port graph and the vented only shows in the rear port graph.. Im still new this obviously.. lol

[Joe X]

The rear chamber is sealed man, air velocity should be zero.

[dsw422]

The rear chamber is sealed man, air velocity should be zero.

Oh ok.. thanks..

So if I go the ported route, should I still keep air velocity below 20??

[Triticum Agricolam]

thanks triticum.. that's the one I downloaded to get the second graph.

so I did what you said.. with same net box size and tuning, the minimum port area to be below 20m/sec is 270 sq in... that's huge for just 2 15s..

anyway.. quick question about WinISD, what is the difference between front and rear port velocity.. I ask this cuz the 4th order only shows velocity in front port graph and the vented only shows in the rear port graph.. Im still new this obviously.. lol

Your second graph shows version .50a7, the one I linked is version .70.

With bandpass boxes all of your sound is coming out that port, its going to need to be big or you will be choking your output. With ported boxes you can get away with a little higher port velocities, but lower is still better. I go as high as 30 m/sec with ported boxes, but I like to keep it less than that. Unfortunately its not an exact science. I can't just tell you that 30 m/sec is OK and 32 m/sec is not. Things like the shape and style of your port, its placement within the box and within the vehicle will all affect how much port velocity will be OK.

[dsw422]

ok.. my computer wont let me download the .70 version..

but I may go ported since the port area for the 4th is way too big..

only thing now, with ported and 130sq in. of port are is over 5 ft port length.. how can i design the port to be that long in the design i have and be efficient??

[Joe X]

Ported,those subs would require much less than that area. Unless you are tuning very low is not going to be 5ft.

[dsw422]

i based the port area from carstereo.com's port area calculator. with 19mm of xmax, 2 15s and tuned to 32hz, it recommends 126.57 sq in.

on the same page it recommends port length of 49 inches.

and according to WinISD, a 5 cu ft net box and port area of 132 sq in, port length needs to be 59.7 in. port velocity will be 29.756 max.

so which one is right??