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Brandon Thompson

EVL 12 - Weird Extended Cab Enclosure

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Hey guys! I'm new here, but not entirely new to car audio. Have spent a while learning how to use WinISD and have a pretty firm understanding of ports, gain, box rise, air velocities, etc. 

I have a very limited space behind the seat of my extended cab Ranger, however lots of tall room. This creates a box that's very upright, and looks very different from most things I've seen. I was wondering if this configuration would make any significant issues? I notice that my output/ transfer function magnitude graph looks very different than what I'd expect out of a ported enclosure built close to manufacture's specifications, too. I expected a peak around tuning frequency ( around 31 hz) and a fall off. Instead, I have a pretty linear graph (which I like) however it seems to try to peak at 40+hz? ( See pictures). 

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Box Design (2.75" Port, 2 cubes of net volume as per Skar's specs and my area limitations)

 

 

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Transfer Magnitude Plot

 

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Rear Port Velocity (m/s)

 

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Cone Excursion (mm)

 

Also, the program says I'll be exceeding XMAX at only 40hz with a 1200W input, which seems off as well. Port velocity peaks at 38m/s, which is close enough to 10% the speed of sound that I'm comfortable with it. Any input on the box design would be great! This will be my first ported box I've ever built. Moving from a 600w sealed setup to a 1200W ported. Thanks!

 

One last thing, does the board where the sub mounts to seem too thin around the edges? It's 12.5 inches wide, and the cutout diameter is 11.25".

Edited by Brandon Thompson
Inserted Wrong Picture

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Hello Brandon, welcome to the forum.  

I plugged your numbers into WinISD and I got a significantly different looking frequency response graph compared to what you got.  What specs did you use for your subwoofer?  If you could post a screenshot of the T/S parameters in WinISD, that would help.  

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1051536683_DriverParameters.PNG.c933aa6acb5672d984ffe57bb6d8f6ff.PNG

Here's a picture of the driver parameters. I filled in what I could off of Skar's website and let it auto calculate the rest. Pretty new to some of these specs so it's possible I threw in a number that was way off. 

 

I also put in a 23hz highpass filter and a 60hz lowpass in WinISD, if that's also useful info. Again just mainly confused by the way the curve looks. Thanks!

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OK, try these parameters:
image.png.a109b6648980537c4c25ca955637c789.png
I've had issues with trying to use more than one voicecoil in WinISD, so I just double the Re and leave the voicecoils as one, like they are wired in series.  

This is the transfer function magnitude I'm getting with a 2.0 cu ft box tuned to 31 Hz:

image.png.ed05dc5d154fbb7e9b65c20c2ba1f6a7.png

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5 hours ago, Brandon Thompson said:

That looks way better, thank you so much for your help!!! Any other suggestions on the box? 

I think your box looks pretty good.  If anything you might add a couple braces from side to side, other than that I'd add 45 degree pieces in the corners of the port path and round over the inside corners to smooth airflow.  

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IMG_20181224_165636-min.thumb.jpg.48f9a0dc57d20eb20a4656abcb7d391c.jpg

I made my first ever ported box today, turned out awesome! Used the stone textured spray paint you can buy in Walmart and it doesn't soak into MDF like other spray paints and leaves a nice texture. Sounds pretty good, but I'm currently having to run it at 4 ohms since my amp isn't 1 ohm stable. So it's only on maybe 350-400 watts :(

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Looks great man!

 

One suggestion, you might try flipping the box around so the port is next to the door. 

Edited by Triticum Agricolam
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Yeah, I was thinking about that.. that's part of the reason I did a port-up subwoofer-up box. I'd assume it'd have better sound wave coupling with the port parallel next to the window just from what I've learned online, I'm by no means an audio engineer though. I know in home audio they try to do something similar. Why does it work like that though? I'd love to learn.

 

I just threw it in there so I wasn't bass-less for now, soon I'll have to take the whole thing out to rewire the sub and install a new amp. When I do that I'll definitely turn the box around, thanks for the suggestion! 

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