Designing a 4th order bandpass with a flat response
Primer:
I'm going to do an article covering 4th order bandpasses. It's format will be similar to my "designing a box with winISD" article. The alignment of the box will be very similar to a sealed box within the 30-80Hz band. This will be not at all like they "typical" 4th order bandpasses with large vented chambers tuned low. This method is for people who like how sealed boxes sound, and want a little more output from their subs. You can typically get about +2-3dB from 30-80Hz over a sealed box. It also allows you to ventilate the motor, for greater thermal Power handling over a sealed box. It also puts a excursion null at tuning, which might net you some mechanical power handling over a sealed box. If you want to win a SPL competition this method is not for you. A ported box will have more peak SPL. If you like how sealed boxes sound, and would like some more output(and don't mind giving up more trunk space) this box is for you.
Step 1: Determine the response you want.
The response of a subwoofer is entirely dependent on the box it is in. This method will show you how to design a box that sounds like a sealed box but with twice the efficiency. If that's what you want you're in the right place. Note that if your sub isn't suitable for use in a sealed box, it isn't suitable for use in this alignment either.
Step 2: Collect the T/S Parameters of potential subs and enter them into WinISD
Alright you're still here! Well then it's time to start modeling responses in WinISD. To do that you'll need some electro-mechanical parameters known as the Theile Small Parameters. These allow WinISD to model the response of the driver. When modeling this enclosure we're going to make some assumptions about cabin gain.
Step 3: Modeling
To start modeling subs you will want to click 'New Project' or CTRL+N.
You will be prompted to select a driver from a drop down menu. Choose one of the drivers you plan on modeling and click next. Then you will be prompted for the number of drivers. Enter the number of drivers and click next.
Next choose the type of enclosure, in this case a 4th order bandpass. Finally you will choose your alignment. Choose 0db ripple 0db passband gain. This isn't critical, since we'll be modifying the alignment later anyways.
Time for the magic. If you chose 0dB ripple and 0dB gain in the previous step then you do not need to adjust the sealed chamber volume. It will be roughly correct. You can fine tune it later.
Otherwise you'll want to enter a sealed chamber volume which results in a Q of .7. (not sure what the volume is to get a Q of .7? go back and model a sealed box with your sub and chose .707 as the Q when prompted).
Now adjust the vented chamber tuning to 65Hz, leave the chamber volume whatever it was before from the previous step. If in doubt make it 1/2 the sealed chamber volume. We'll fine tune this later.
Now it's starting to look like a the sealed response, from 30-80Hz.
Step 4: Apply Cabin Gain, SSF and LPF In this step we will be applying some filters to simulate cabin gain, the sub sonic filter on the amp, and the high pass filter on the amp. If you're not sure how to apply these filters check out my other post: http://forum.realmofexcursion.com/en...ar-winisd.html
Note how similar the shape of the two curves are. In case it's not clear:
In our region of interest, 30 - 80Hz, there is at least 3dB gain. On an advanced note, if your amp has a 24dB/oct LPF the combined rolloff will now be 36dB/oct. That may cause issues blending with your front stage. So you may want to increase the LPF freq on the amp. Or if possible set it to 12dB/oct. If it was me, I'd turn the LPF on the amp all the way up, and set the LPF on my head unit to 12dB/oct at 80Hz. The 36dB/oct combined roll of is partially responsible for the difference in response between the two boxes above 60Hz or so.
Step 5: Adjust the tuning and volume It doesn't work out as easily as above. If the subwoofer has a large VAS, a qts that isn't around .4, or other extreme parameters it may require some fine tuning. Sometime subs aren't suitable for this alignment. But for most typical mid-Q subs, this will work.
The box we came up with above has some very odd measurements. Let's convert it to nicer numbers. 2cuft sealed, 1cuft vented at 65Hz. That didn't change things too much.
__________________
Car: 2009 Audi A4 Avant Quattro
Sub amp: Hifonics ZXX-3200.1D
Subwoofers: 4 SA8V.2 @ 2 Ohms
Enclosure: 2 cu ft ported, tuned to 33Hz
Re: Designing a 4th order bandpass with a flat response
Yup, can't give away the golden goose.
Either that or I got really sick of typing.
Oh and the screen caps, those are a pain too.
__________________
Car: 2009 Audi A4 Avant Quattro
Sub amp: Hifonics ZXX-3200.1D
Subwoofers: 4 SA8V.2 @ 2 Ohms
Enclosure: 2 cu ft ported, tuned to 33Hz
Re: Designing a 4th order bandpass with a flat response
It was mentioned I should address port area.
I like to keep the vent velocity below 30m/s between 30-80Hz.
The rule of thumb 16 sq in /cu ft of port area usually achieves this for moderate systems. For a typical 12" sub and 1500Wrms it's usually fine.
But it's good to check the vent velocity graph in winISD. If it's going over 30m/s, then you're Qp is going to drop. Which in turn will decrease the output. This leads to port compression. It's similar to thermal Power compression. When you increase the power by 3dB you might only gain 1dB in output. Measuring the Qp of a port is difficult. It's much easier to just use adequate port area from the start.
__________________
Car: 2009 Audi A4 Avant Quattro
Sub amp: Hifonics ZXX-3200.1D
Subwoofers: 4 SA8V.2 @ 2 Ohms
Enclosure: 2 cu ft ported, tuned to 33Hz
Last edited by Fallen; 10-10-2012 at 08:04 PM.
Reason: Too complicated
Re: Designing a 4th order bandpass with a flat response
Fixed. I'll post the image in your thread Beck.
__________________
Car: 2009 Audi A4 Avant Quattro
Sub amp: Hifonics ZXX-3200.1D
Subwoofers: 4 SA8V.2 @ 2 Ohms
Enclosure: 2 cu ft ported, tuned to 33Hz
Re: Designing a 4th order bandpass with a flat response
So I figured since you helped me see in my Iso thread how it wouldn't work out I figured I would try your step by step to possibly see where I went wrong when building my first 4th... Which I pretty much built to sub specs. Together they called for 1^ft sealed, 1.75 ported which is what I did... I tried to model this in winisd and when I go to look up any of my subs they aren't there... So I tried to enter them in the database but they refuse to let me type anything in... Am I doing something wrong? I am using version .44 if that matters...
Re: Designing a 4th order bandpass with a flat response
Quote:
Originally Posted by Slobalt7
So I figured since you helped me see in my Iso thread how it wouldn't work out I figured I would try your step by step to possibly see where I went wrong when building my first 4th... Which I pretty much built to sub specs. Together they called for 1^ft sealed, 1.75 ported which is what I did... I tried to model this in winisd and when I go to look up any of my subs they aren't there... So I tried to enter them in the database but they refuse to let me type anything in... Am I doing something wrong? I am using version .44 if that matters...
you dont just use the sealed and ported recommendations...that is a fairly awful idea.
check the sticky for winisd. it shows you which params to input. Certain params are calculable based on others,(qe qts, vas, etc) and it there is a conflict between what winisd has calculated and what you entered(even if it is a discrepancy of .00001) it will trigger an error message
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Re: Designing a 4th order bandpass with a flat response
Quote:
Originally Posted by smfonic1
Don't put to much into Winisd, let it solve the missing parameters for you.
It is tricky, I agree with that.
Agreed.
The QB3 alignment might be ideal for in houses, but with cabin gain it just gives you a bloated low end.
...
But then again I like a somewhat bloated low end hahaha.
Anywho with subs with extreme specs, it'll often give dumbass recommendations.
__________________
Car: 2009 Audi A4 Avant Quattro
Sub amp: Hifonics ZXX-3200.1D
Subwoofers: 4 SA8V.2 @ 2 Ohms
Enclosure: 2 cu ft ported, tuned to 33Hz
Re: Designing a 4th order bandpass with a flat response
Quote:
Originally Posted by cxa0897
you dont just use the sealed and ported recommendations...that is a fairly awful idea.
check the sticky for winisd. it shows you which params to input. Certain params are calculable based on others,(qe qts, vas, etc) and it there is a conflict between what winisd has calculated and what you entered(even if it is a discrepancy of .00001) it will trigger an error message
Oh Trust me I found that out, Wasted a couple sq ft of 3/4 because at the time I didn't know what I was doing... Rebuilt the box using the scrap from the first one and built a pretty decent but leaky ported box. Fixed the leaks and it hits pretty well but too peaky because I tuned too high(48htz-ish).
Quote:
Originally Posted by Fallen
Anywho with subs with extreme specs, it'll often give dumbass recommendations.
So I figured out how to throw my Skars in there but I can not find any t/s's on my MA80xe's. I developed a 4th for the Skars last night although IDK if I will make it or not, it seems quite [email protected], [email protected], [email protected] Without any t/s's IDK what to do with the MA80's. I know they are some relatively obsolete subs but they still have good spiders and maintain a more consistent volume through a wider range than the MA-8's in the same sealed box...
Re: Designing a 4th order bandpass with a flat response
Quote:
Originally Posted by Slobalt7
Oh Trust me I found that out, Wasted a couple sq ft of 3/4 because at the time I didn't know what I was doing... Rebuilt the box using the scrap from the first one and built a pretty decent but leaky ported box. Fixed the leaks and it hits pretty well but too peaky because I tuned too high(48htz-ish).
So I figured out how to throw my Skars in there but I can not find any t/s's on my MA80xe's. I developed a 4th for the Skars last night although IDK if I will make it or not, it seems quite [email protected], [email protected], [email protected] Without any t/s's IDK what to do with the MA80's. I know they are some relatively obsolete subs but they still have good spiders and maintain a more consistent volume through a wider range than the MA-8's in the same sealed box...
__________________
Car: 2009 Audi A4 Avant Quattro
Sub amp: Hifonics ZXX-3200.1D
Subwoofers: 4 SA8V.2 @ 2 Ohms
Enclosure: 2 cu ft ported, tuned to 33Hz
Zomg... Not nuthugging or anything but I think you have helped me on everything I have asked... We should make a search engine like Google but only for audio and name it Fallen. lol.
Re: Designing a 4th order bandpass with a flat response
:P but Fallen just uses google.
Hahaha.
__________________
Car: 2009 Audi A4 Avant Quattro
Sub amp: Hifonics ZXX-3200.1D
Subwoofers: 4 SA8V.2 @ 2 Ohms
Enclosure: 2 cu ft ported, tuned to 33Hz
Re: Designing a 4th order bandpass with a flat response
Oh damn it. I use google and can't find ****....
As a side note: how do you introduce filters? I don't seem to have a tab like in the tutorial... And, how do you narrow your graph, I am modeling subs, I don't really care about how it sounds above 100htz(that is what my mids are for right now until I get some sophisticated **** and use midbass woofers) but it models to 1000...
Re: Designing a 4th order bandpass with a flat response
Okay, I'm debating on building my first 4th order setup with my IAD 15. I have read the the 4th Order Flat Response Sticky thoroughly, but I have some questions. For example, if I follow the sticky thread using the general cabin gain filter, I use 3 cubes on the sealed side and 1.5 cubes on the ported side tuned 60 hz, that gives me a flat response and rises around 50-60 hz. If I design a 4th in the program with 2.5 cubes sealed and 5 cubes ported tuned 60, it peaks at tuning. I've been researching and most people run double the volume on the ported side versus sealed/2:1 ratio. According to WinISD, that should peak at tuning of the vented side with the cabin gain filter applied, but everyone says they get nasty on the low frequencies. Any idea as to why WinISD shows a 2:1 (Ported to sealed) ratio 4th order peak at tuning?
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Vehicle: 2012 Dodge Ram Express SCSB 5.7 2WD
NO AUDIO AS OF YET! :/
Previous Setups: 2 CVR15D4 on Hifonics Brutus 1000D @ 1ohm tuned to 35hz, 2 DD1508D4 @ 35hz on Hifonics Brutus 1500D, 2 GPV12D4s @ 33hz on DSC2000.1D, 1 GPV12D2 @ 33hz on HTG2600D, 1 RE SE15D2 2 cubes sealed on HTG2600D. RE SE15 [email protected] on Brutus 1000.
Current: Incriminator Death Penalty 12D2 on Skar SK-1500, 2ft^3 tuned 35.5hz
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