First Box Build WinIsd Question.

[SpydreX]

Building a ported box for two Sundown Audio X 18s in my 97 Jeep Grand Cherokee. I wanted to tune the box to 30Hz and have around 6ft^3 of airspace for each driver. To build a box big enough I was planning on making the box conform around the wheel wells meaning that the lower section of the box would be 42" long 9" tall and 25" deep, the top would be 50" long 18" tall and 25" deep. So the top goes over the wheel wells while the bottom goes in between them if that makes since.

Port will be 40.5" tall 4" wide and 30" long to achieve somewhere close to 30Hz. Box dimensions take into account sub woofer, port, and 45 bracing displacement. Oh yeah and I will be up firing subs port firing back if that matters at all.

WinIsd is throwing me a weird transfer function magnitude so I was hoping y'all would take a look.

I also wanted y'all to see if my port velocity is good or not.

[Triticum Agricolam]

Your tuning must be off in WinISD. From the graphs you are tuned to like 150 hz.

[SpydreX]

Your tuning must be off in WinISD. From the graphs you are tuned to like 150 hz.

Do you think its just the program? I made sure to set tuning to 30Hz

I just don't want to end up building the box and then realizing after the fact that i've screwed something up.

[Triticum Agricolam]

I've never had WinISD let me down when the information its given is correct.

There is a newer version of WinISD you might try and see if that fixes the problem, you can get it here: http://www.linearteam.org/temp/winisd-07x.exe

[SpydreX]

I've never had WinISD let me down when the information its given is correct.

There is a newer version of WinISD you might try and see if that fixes the problem, you can get it here: http://www.linearteam.org/temp/winisd-07x.exe

Thanks for the download I will try it out and let you know if anything changes or not.

[SpydreX]

I've never had WinISD let me down when the information its given is correct.

There is a newer version of WinISD you might try and see if that fixes the problem, you can get it here: http://www.linearteam.org/temp/winisd-07x.exe

Well I typed in all my parameters and information and the transfer function magnitude is a lot more acceptable now but still seems a little high. Also it is giving me a very short port length auto calculated to 2.96in.

My port velocity also seems to be very high.

[SpydreX]

Oh shit wait, while reviewing my post I just realized my port is in centimeters instead of inches. Oops... Well Transfer function magnitude is still high but port velocity is back down to around 25.6 m/s.

[Triticum Agricolam]

If you want to reduce the peak in your transfer function magnitude you can reduce the box size, tune lower, or do a combination of both.

[SpydreX]

If you want to reduce the peak in your transfer function magnitude you can reduce the box size, tune lower, or do a combination of both.

One thing I am confused about is where the peak is at, around 40Hz so does that mean my box will actually be tuned to 40Hz? I was playing with some different sizes and to get it to peak at 30Hz I had to punch in 50ft^3 which is obviously unrealistic. any time I decrease the tuning frequency on the box the peak frequency never changes.. All it does is flatten out the peak so what exactly is the transfer function magnitude? Is it my tuning, where the bass hits the hardest, or is it suppose to match my frequency?

[Triticum Agricolam]

The transfer function magnitude is just a graph of the frequency response of the sub & enclosure.

Where your box peaks at and where its tuned to are not the same thing, as the graph is showing. Ported boxes are a resonant system and the tuning is the frequency at which the system resonates. Where you get peak output is going to depend on a lot of different factors, box size and tuning being some, but not all, of them.

WinISD only shows you raw output from your sub, once you put it in a vehicle cabin gain is going to change the frequency response significantly. Most likely shifting your peak frequency down.