The dual reflex...like the picture in winISD is showing

 

What's your group delay and port sizes?

 

Group delay graph uploaded.

 

Thanks. What do you think of the graph? I'm not sure why the attachment came out so small because it is actually a large screenshot.

 

See port sizes so far. This is still subject to change.

 

My question is how you are going to get a 4.5 foot long port to work right? That's not a good idea.

The FR looks good, but that's about it. I myself wouldn't build that box.

 

Yeah the port sizing is subject to change. But so far after some more tweaking i came up with a slightly bigger box and shorter ports and a frequency response with a better low end extension. So i've come up with a box size of roughly 40x14x14 which is about 4 inches to long for vehicle, but i can increase the box height instead to compensate.

What do you look for in the group delay graph?

 

That one port is still nearly 4 feet long. Way too long for the port area.

The general rule of thumb is if the speaker has good specs for sealed then it would do ok in a 4th order, and if it models well ported then it would do ok in a 6th order.

I don't think that speaker is very well suited for ported enclosures.

 

Alpine type R is better off in 4th order bandpass.


Sixth order, is the addition of another chamber, and another vent, from 4th order.

dual reflex band pass is easier to understand.

It gets complicated way too fast, I believe JL Audio has a tutorial on vented alignments that explains it well.


you have 3 cubic feet in which to put a dual chamber enclosure, and deciding on how you want to shape your response, makes a difference on everything.

to make it a high-gain box, or "one note wonder" you make the vented side bigger than the sealed side.

to make it a good balance between efficiency and musicality, you make the two sides relatively equal.

to make a smooth, low peak, sound quality box, you make the vented side smaller than the sealed.


these are just rough guidelines and do not hold true for every sub, but it should give you some idea how to start separating the box into sections and then tuning for a graph that looks like a plateau and not a mountain range.

 

I couldn't get it to model how i wanted in a 4th order, not enough low frequency response so that's why i tried 6th. Hatedguy, it actually models quite well in a ported which is what i'm currently using. See curve below: the white line is ported and the yellow is 6th order bandpass and the blue is 4th order.

 

For the 4th order: you need to increase the size of your rear (sealed) chamber to get frc down to 45ish for maximum low-end extention. Then tune you front chamber to the frc frequency and adjust slightly from there. You don't have nearly enough airspace to produce anything that will sound good.

For the 6th order: Not even remotely enough space. Unless you can devote a solid 4+ cubic feet don't even bother. BTW there are two types of 6th order enclosures: a parallel tuned (the "dual reflex" design), and the series tuned ("quasi 6th"). WinISD can only model a parallel design, but a quasi design needs as much airspace so it's kind of a moot point.

 

The port for that ported box will be too long for the area to be really effective...just taking a wild guess. You are going to need to make the enclosure much larger to get a port to have a length to work right.

 

Presently the sub is in a 1.7 cubic ft box tuned to 28Hz with a vent length of 46 inches. This isn't much different than the rear chamber for the 6th order which i have modeled as 1.6 cubit ft tuned to 25. The vent length is actually shorter at 30" because i used a slightly smaller vent area.

The sub is designed to play well in small enclosures tuned low. Alpine recommends 1-1.5 cubic ft tuned 32-37hz.

 

the Q-logic bandpass box designed as a pre-fab, universal fit model used 1.82 cubes, with vented taking .98 and sealed .84 cubes using 2 - 4" vent tubes.

Many people found this box was a bit peaky and not quite large enough to present a sound quality, or less boosted response.

If you add just .2 cubes to each chamber, it would help make a lot more subs sound more musical.

I wouldn't attempt to run that 12" sub in a box with less volume than the Q-logic "standard" box, and after looking at the "fit sheet" Q-logic supplies with the box, I'd probably use a similar ratio of sealed to vented for a bigger box, using slot venting.

so, something like .94 sealed, 1.1 vented might be enough using a single 6" round vent, or something similar in the slot.