SoundQubed Jeep Grand Cherokee Laredo 2014

[Charles Phillips]

Hello, internet. I'm a college kid helping a friend of mine with a build in his Jeep. This is my 4th build, but my first posted build so go easy on me. We're all here to learn.

This is meant to be a budget build that may or may not be incrementally upgraded. He's had a few Rockford Fosgate prefab setups in the past, but wanted something a bit bigger. Our equipment currently consists of:

- 2x SoundQubed HDS-2.110 (600W RMS / piece) $120 / each

- 1x SoundQubed Q1-1200.2 (1300W @ 14.4v)     $200 used

- 1x 4 gauge CCA amp wiring kit                           $40 used

- 1x large sheet of birch plywood                          $50

Over the course of the past few weeks, we've agreed that an isobaric 4th order bandpass is the best solution to our problems of space, since he didn't want the size of a ported box, but thought a sealed box wouldn't play low enough. Since I'm still technically in the testing stage, I'm still not sure that a 4th order will fit the size requirements, but on paper it's looking alright so far. I'll get more details when I touch base with him tomorrow. A goal of mine was to be able to document a 4th order isobaric design and have a list of calculations that works for everyone. I apologize for no pictures in my first post, but I assure you they will be here ASAP. So, with no further ado...

 

STEP 1: Deciding on a goal
We want a fairly linear response over a wide frequency range at the expense of SPL. Sometimes less is more. My thought was that the nonlinearity I would sacrifice by going with somewhat degraded transients would be possibly smoothed out by the choice to go isobaric. Since the two drivers become acoustically paired together by the small amount of air between them, they're treated as one distinct transducer, and the mechanical parameters change to reflect that.

STEP 2: Choosing the amount of ripple

There are countless sources which indicate that certain "S" values correspond to certain acoustic crossovers. I decided not to go with 0.707 and exchange transient response for a wider pass band that can be smoothed out, deciding that 0.6 would be a good start for experimentation. In conclusion, S = 0.6.

STEP 3: Determining the bandwidth and thereby, sensitivity

To find these, you have to reference the chart I will include a link to at the bottom of this post. Firstly, you have to find the fL, or lower -3dB point. This is the lower part of the passband where the frequency response drops off rapidly (compared to sealed or ported boxes). I'll post all of the formulas I used and my work in case anyone else is interested in my results.
fL = F(s) / Q(ts) * (fL factor)
fL = 31.63 / 0.519 * 0.4827
fL = 29 Hz low cutoff (0 dB gain)

Then we determine the high cutoff. The sealed section of the box helps reproduce the low end while the ported section acts as a filter and assists reproduction of the high end.
fH = F(s) / Q(ts) * (fH factor)
fH = 31.63 / 0.519 * 1.4387
fH = 87 Hz high cutoff (0 dB gain)

So wow, we end up with an effective range of about 32 hz - 80 hz before cabin gain (keeping in mind that the points dictated as -3dB will be half as loud as frequencies within the passband. This suits our needs perfectly!

STEP 4: Find the volume of the ported chamber

I did this part in liters and then realized I was in America.

Vf = (2S * Q(ts))^2 * V(as)
Vf = (2(0.6) * 0.519)^2 * 56
Vf = 21.721271 liters = 0.767079446132 ft^3 = ~0.77 ft^3

STEP 5: Find the volume of the sealed chamber

Vr = V(as) / ((Qbp / Q(ts) )^2 - 1)
Vr = 56 / ((0.8333 / 0.519)^2 - 1)
Vr = 35.4899442 liters = 1.253315551387 ft^3 = ~1.25 ft^3

STEP 6: Calculate front chamber tuning frequency

fb = Qbp * (F(s) / Q(ts))
fb = 0.8333 * (31.63 / 0.519)
fb = 50.784738 hz

STEP 7: Calculate port dimensions

Since this box will be slightly bigger than the aforementioned specifications to account for the volume taken up by the sub basket and magnet assembly, we still need a small port. After all, the bigger the port is, the longer it needs to be. There's a relatively simple equation out there that calculates the air speed at the port to determine if it needs to be bigger, but I've assumed ~4" would be appropriate.

R = 5 cm (10 cm diameter)
Lv = ((94250 * R^2) / (fb^2 * Vf)) - (1.595 * R)
Lv = ((94250 * 5^2) / (50.784738^2 * 21.721271)) - (1.595 * 5)
Lv = ((2,356,250) / (56,021.1044)) - (7.975)
Lv = (42.0600419) - (7.975)
Lv = 34.0850419 cm = 13.41930783465 inches long port x 3.93701 inches wide

CONCLUSION OF FIRST CALCULATIONS:

This is an example with one of the two SoundQubed subs in use. I will make a subsequent post where I will change these parameters for application in an isobaric setting, and make sure we document the proper way to wire the line out converter since we will not be replacing the radio.

SOURCES:
http://audiojudgement.com/4th-order-bandpass-design/
http://images.audiojudgement.com/2016/03/4th-order-bandpass-ripple.jpg

 

[Charles Phillips]

Back at it again! Since I wanted to have an easy way to find 4th order specs without a bunch of repetitious calculations, I decided to program a calculator in Java. It's pretty good for a nice quick design for a 4th order bandpass with one sub, but can be scaled if you know what you're doing with basic math. You still have to use an external source (included) to find the minimum port diameter (I've been coding for 3 hours, don't hate). Otherwise, it's nifty and will save you quite a bit of time. Best of all, it's free! Hope this helps someone out. Running some experiments with a leftover HDS-312 to decide if isobaric would just be more of a pain than it's worth.

 

Here's the link to my 4th order calculator:

https://drive.google.com/file/d/0B4nVZk8knWyIQTFOQU1Jb18wNTQ/view?usp=sharing

Google scans all files under 100 MB (this one is very small) for viruses, so no worries about that.

 

Sidenote: You'll need JRE (java runtime environment) to run my .java file.

[WalledSonic]

What are your references/sources for this calculator? Why not just use winisd?

[BP1Fanatic]

or Hornresp???

[Triticum Agricolam]

I thought you decided to go with a ported box?

[BP1Fanatic]

BR is boring. BP is where's it @!

[Charles Phillips]

On 6/30/2017 at 2:30 PM, WalledSonic said:

What are your references/sources for this calculator? Why not just use winisd?

 

On 6/24/2017 at 11:56 PM, Charles Phillips said:

SOURCES:
http://audiojudgement.com/4th-order-bandpass-design/
http://images.audiojudgement.com/2016/03/4th-order-bandpass-ripple.jpg

I didn't want to use WinISD or HornResp right away because I wanted a better understanding of what I was doing and why those calculators make certain things the way they do.

 

On 6/30/2017 at 7:31 PM, Triticum Agricolam said:

I thought you decided to go with a ported box?

 I did, and after seeing the large port we have to deal with, we've revised our strategy a bit.

 

 

[Charles Phillips]

After designing a ported isobaric box that had a very large port (9 inch diameter and 112 inch length) we decided that since the most he's had in the car before was some 100 watt amp and an Rockford Fosgate sub, one 10" would probably be enough on 600 watts. However, to make sure, I have a box sitting around for 2 12's that is about right for them. I'll adapt that box and see if he's willing to give up space for bass. In the end, if we decide on one sub in the car, the other one will go in his boat or as a home theater sub in some sort of bandpass or horn. 

For all those people with two SoundQubed HDS-2.110's wondering what to do with them, my results from BassBox Pro 6 are quite telling. They indicate strongly that a hi-fi design gives strong SPL and a very acceptable frequency range to play with. You only give up having a huge peak at a few frequencies which is expressed in the loudness optimized setting. I've included the specs here in case I've made any huge errors, which is very possible given how big the port is.
 

[Triticum Agricolam]

So just to make sure I'm on the same page as you,  you are proposing a 1.75~ cu ft box, tuned to 28.8 Hz for two HDS210 subs on 1300 watts.  Is that correct?

Assuming that info in correct, you neither need nor want a 60 sq in port for that setup.  Its too much, and I don't get to say that very much.  A 112" long port is going to cause you problems.  Once you get much over 44" or so you can start to run into pipe resonance issues.  Also, you don't need that much port area to keep port velocities under control.  A 30 sq in port will get the job done, and even it is going to be pretty long.  

These really small, low tuned boxes are where a t-line starts to make sense.  

[BP1Fanatic]

Can you post the HR response to your latest build TA? That's an interesting looking FLH!