On axis 6th order assistance

[8ten8]

As an experiment, I'd like to use my old 15 (AB xd1522) and build a on axis 6th around it. My goal is, w/ the 900w I have, to get down in the 20's with authority and hit the 40's or 50's as well. If it works to my liking, I would build another for my future set-up. Assistance is needed on this as I suck at the math part. Specs for the 15: Fs 31hz,  Qts .575,  Qes .669, Qms 4.082, Vas 82 liters. Max dimensions: 30" D x 42" W x 20" H. 2002 Outback. Thanks gents 

 

[Triticum Agricolam]

I'm not sure what you are referring to by "on-axis". 

Are you looking for a parallel-tuned or series-tuned box?

[8ten8]

17 minutes ago, Triticum Agricolam said:

I'm not sure what you are referring to by "on-axis". 

Are you looking for a parallel-tuned or series-tuned box?

Parallel. The references I found online did not include pvc. Just normal  ports on eachside of the enclosure. DBdynamixaudio call it on-axis 6th order  parallel bandpass 

[Triticum Agricolam]

1 hour ago, 8ten8 said:

Parallel. The references I found online did not include pvc. Just normal  ports on eachside of the enclosure. DBdynamixaudio call it on-axis 6th order  parallel bandpass 

OK. I gotcha.  I looked up the stuff on DBdynamixaudio.com.  I see why they call it "on-axis" but they are the only people I know that do that.  "on-axis" has a very specific meaning in the audio world and it generally doesn't apply to subwoofers, which is why it threw me off a bit.  

 

Unfortunately your sub has a bit of a low EBP, which is going to make it tough to get good low frequency output in a 6th order bandpass.  Increasing the size of the rear chamber helps, but you can only go so big before cone excursion gets too high. My suggestion would be 4 cu ft tuned to 25 hz for the rear chamber and 2 cu ft tuned to 50 hz for the front chamber.  Both chambers should have port area of at least 35 sq in.  Depending on how much cabin gain you get you should get good output from the mid 20's up to 60 hz or so.  

 

[8ten8]

1 hour ago, Triticum Agricolam said:

OK. I gotcha.  I looked up the stuff on DBdynamixaudio.com.  I see why they call it "on-axis" but they are the only people I know that do that.  "on-axis" has a very specific meaning in the audio world and it generally doesn't apply to subwoofers, which is why it threw me off a bit.  

 

Unfortunately your sub has a bit of a low EBP, which is going to make it tough to get good low frequency output in a 6th order bandpass.  Increasing the size of the rear chamber helps, but you can only go so big before cone excursion gets too high. My suggestion would be 4 cu ft tuned to 25 hz for the rear chamber and 2 cu ft tuned to 50 hz for the front chamber.  Both chambers should have port area of at least 35 sq in.  Depending on how much cabin gain you get you should get good output from the mid 20's up to 60 hz or so.  

 

Awsom, very nice! I'm going with your recommendation.  I haven't used Torres before. Assuming Torres is mobile friendly. What would be your recommendation to figure the plans out? The port and displacement of motor, port and bracing is  where it gets screwy for me. 

[Triticum Agricolam]

3 hours ago, 8ten8 said:

Awsom, very nice! I'm going with your recommendation.  I haven't used Torres before. Assuming Torres is mobile friendly. What would be your recommendation to figure the plans out? The port and displacement of motor, port and bracing is  where it gets screwy for me. 

Torres is PC only, its not mobile friendly.  It would be tough to use to figure out this style of box anyway. 

There are multiple ways to layout a box like this, here is one idea:

The outside dimensions are 42" wide, 18" tall, 21" deep. All panels except the top and bottom are 16.5" wide.  The top and bottom are 42" x 21".  The ports are 2.5" wide.  

[8ten8]

2 minutes ago, Triticum Agricolam said:

Torres is PC only, its not mobile friendly.  It would be tough to use to figure out this style of box anyway. 

There are multiple ways to layout a box like this, here is one idea:

The outside dimensions are 42" wide, 18" tall, 21" deep. All panels except the top and bottom are 16.5" wide.  The top and bottom are 42" x 21".  The ports are 2.5" wide.  

Thank you so much Triticum! I'm literally grinning from ear-to-ear

[Joe X]

Modeled that and here's what Ive got, generic cabin gain applied:

 

Seems like there's a rather fast roll-off beyond 35-37Hz or so in my modeling, if one is interested in more gain at higher frequencies and a seemingly smoother response I would suggest a front chamber of 2.5net @ 55Hz which would model like this:

 

 

 

[8ten8]

7 minutes ago, Joe X said:

Modeled that and here's what Ive got, generic cabin gain applied:

 

Seems like there's a rather fast roll-off beyond 35-37Hz or so in my modeling, if one is interested in more gain at higher frequencies and a seemingly smoother response I would suggest a front chamber of 2.5net @ 55Hz which would model like this:

 

 

 

Ooo that's nice. How would I go about making the adjustments? 

[Joe X]

The easiest way would to do that mod would be making the chamber on the right a little wider and adjusting the port length on that chamber to the new tuning considering the increased internal airspace.