How to/what to consider when designing 4th order bandpass

[20 hz bass machine]

First things first you need modeling software! Without it you will not be able to dial in the enclosure properly.

Secondly, you need to make sure that you're using a sub that is suited for sealed applications. You can determine this by calculating the EBP (FS/Qes). An EBP below 50 is ideal but technically anything between 50&100 will fit the bill.I personally never go with a 4th order if the EBP is above 75.

After you've chosen a sub, you have a lot of factors to consider. Everything you do will change the design of the box and need to be accounted for.

Now you need to determine how much space you have/how much you're willing to give up.

From there I input the driver into my modeling software (BB6 in my case) and start by modeling a sealed enclosure in order to determine what the Q factor of my sealed section will be.

At this point I decide on a sealed section volume. I usually shoot for a Q of .707 although depending on box size, space available, power being used, and desired ratio. That is liable I change.

Once you've decided on a sealed side volume, yo will move over to 4tg order design and input your decided sealed volume.

This should give you a sealed side resonance. That resonance is what you tune your vented chamber to.

From there it's simply a matter of modeling the vented chamber to your desired ratio making sure to size the port properly and accounting for all internal displacements.

You'll notice that ass you change the tuning, the port changes, which changes the net volume which changes the ratio slightly which changes even more variables. All of which need to be accounted for and addressed before coming to a finished product.

There's a lot more to it than just this but I figured it would help someone who's just trying to get their feet wet

 

[Buck]

Sealed peak resonance is Fc or Fsc or in a 4th order bandpass could be called Frc. I always check what a woofer's Fsc and Qtc are in sealed to determine how they will play in a 4th order bandpass.

Over say 1000-1500w, I also recommend inverse mounting the woofers (motor in ported chamber) to help motor and coil cooling.

Also, depending on the the quality of the woofer or strength, you may want to do individual sealed chambers for each sub. Some of the higher quality, well made subs can all share one large sealed chamber with each other. Some lower powered/softer subs or cheaper-made subs can have issues being damaged by having a bunch of subs all compressing air in the same chamber. Cones and surrounds can blow out or break, in some situations. One large sealed chamber will resonate lower than the same amount of airspace divided up into multiple chambers, so keep that in mind.

Ported to sealed ratio is a farce; that's a doodoo way to determine a 4th order bandpass. Both sealed and ported airspaces should be considered based off how much air the subs can properly pressurize, not a ratio.

You can tune the ported side to the sealed resonance, or you can tune differently. It just depends on what the sealed resonance is and what your overall goals are for the system.

Most of the higher powered subs will do better in ported boxes or series 6th orders, but there are some higher powered subs (say 3000w+) that will work being played in a sealed chamber.

Don't do too much port area on your 4th order. Often times, they don't need as much as people think they do, from what I've seen. It depends; a b-pillar 4th order wall's port area is going to work somewhat differently than a smaller 4th order bandpass. If you want a musical response, go with a proper amount of port area. It's the same idea with any ported chamber: your port area can determine overall bandwidth and peakiness, so it's important to know what kind of port area you need. A 500w sub in a 4th order is going to probably need less port area than a 3500w sub.

 

[20 hz bass machine]

Sealed peak resonance is Fc or Fsc or in a 4th order bandpass could be called Frc. I always check what a woofer's Fsc and Qtc are in sealed to determine how they will play in a 4th order bandpass.

Over say 1000-1500w, I also recommend inverse mounting the woofers (motor in ported chamber) to help motor and coil cooling.

Also, depending on the the quality of the woofer or strength, you may want to do individual sealed chambers for each sub. Some of the higher quality, well made subs can all share one large sealed chamber with each other. Some lower powered/softer subs or cheaper-made subs can have issues being damaged by having a bunch of subs all compressing air in the same chamber. Cones and surrounds can blow out or break, in some situations. One large sealed chamber will resonate lower than the same amount of airspace divided up into multiple chambers, so keep that in mind.

Ported to sealed ratio is a farce; that's a doodoo way to determine a 4th order bandpass. Both sealed and ported airspaces should be considered based off how much air the subs can properly pressurize, not a ratio.

You can tune the ported side to the sealed resonance, or you can tune differently. It just depends on what the sealed resonance is and what your overall goals are for the system.

Most of the higher powered subs will do better in ported boxes or series 6th orders, but there are some higher powered subs (say 3000w+) that will work being played in a sealed chamber.

Don't do too much port area on your 4th order. Often times, they don't need as much as people think they do, from what I've seen. It depends; a b-pillar 4th order wall's port area is going to work somewhat differently than a smaller 4th order bandpass. If you want a musical response, go with a proper amount of port area. It's the same idea with any ported chamber: your port area can determine overall bandwidth and peakiness, so it's important to know what kind of port area you need. A 500w sub in a 4th order is going to probably need less port area than a 3500w sub.

Love the added input. Agree with everything you said. Always a help on here buck! You should see some of my newer designs, I've gotten a lot better. Starting to become known locally as the "king of 4ths". I have a lot more to learn but I've been learning a lot

 

[20 hz bass machine]

 

[Buck]

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Hahaha remind me of this, slide in wall for 4 sundown either x-12's or zv5 12's:

Idk if I'm ready to give away specs yet lol. I cherish my hard work in teaching myself how all of this works.

4th orders are actually pretty easy, if you have the right subs for a 4th order. Speaking roughly, a lot of musical 4th order bandpasses I've done wind up in a 1.5-2:1 ratio ported to sealed. Just depends on what the sub wants for each. By far the most important part of a 4th order is the sealed chamber.

People get it stuck in their heads how 4th's work. 4th's can work however you want them to. Look at home audio 4th's, where sometimes the sealed chamber will be 3x larger than the ported, lol.

 

[Buck]

Biggest mistakes I see with 4th order bandpasses:

1. Too small of sealed chamber
2. Too large of ported chamber
3. Too much port area

 

[Big_Dan_T]

Sealed peak resonance is Fc or Fsc or in a 4th order bandpass could be called Frc. I always check what a woofer's Fsc and Qtc are in sealed to determine how they will play in a 4th order bandpass.

Over say 1000-1500w, I also recommend inverse mounting the woofers (motor in ported chamber) to help motor and coil cooling.

Also, depending on the the quality of the woofer or strength, you may want to do individual sealed chambers for each sub. Some of the higher quality, well made subs can all share one large sealed chamber with each other. Some lower powered/softer subs or cheaper-made subs can have issues being damaged by having a bunch of subs all compressing air in the same chamber. Cones and surrounds can blow out or break, in some situations. One large sealed chamber will resonate lower than the same amount of airspace divided up into multiple chambers, so keep that in mind.

Ported to sealed ratio is a farce; that's a doodoo way to determine a 4th order bandpass. Both sealed and ported airspaces should be considered based off how much air the subs can properly pressurize, not a ratio.

You can tune the ported side to the sealed resonance, or you can tune differently. It just depends on what the sealed resonance is and what your overall goals are for the system.

Most of the higher powered subs will do better in ported boxes or series 6th orders, but there are some higher powered subs (say 3000w+) that will work being played in a sealed chamber.

Don't do too much port area on your 4th order. Often times, they don't need as much as people think they do, from what I've seen. It depends; a b-pillar 4th order wall's port area is going to work somewhat differently than a smaller 4th order bandpass. If you want a musical response, go with a proper amount of port area. It's the same idea with any ported chamber: your port area can determine overall bandwidth and peakiness, so it's important to know what kind of port area you need. A 500w sub in a 4th order is going to probably need less port area than a 3500w sub.

What would ya charge for an enclosure design? Current setup is an 08 hhr ss with 300 amp alt, 2 agm's, about 500 rms between doors on timpano mids, 3k rms on skar zvx12v2 d2's @.5 to get the 3k. Box is 5.4 cubes slot port at 34. Box built for american bass xfl and needs more port area cause I get alot of port noise now. Wanna go with a wall at the c pillar and take the whole hatch. Goal is demo car. Good range but decent spl. Listen to rock when not showing but dubstep at carshows alot. Debate 4th or 6th. Skar says on site that the zvx isn't reccomended for sealed but when asked about a 4th they recommended 1.25 to 1.5 sealed and 40 inches of port area for ported section. The sealed sizes seem pretty small to me for such a large woofer tho.... but I have never done a 4th or 6th so I don't know..... ????

 

[Buck]

What would ya charge for an enclosure design? Current setup is an 08 hhr ss with 300 amp alt, 2 agm's, about 500 rms between doors on timpano mids, 3k rms on skar zvx12v2 d2's @.5 to get the 3k. Box is 5.4 cubes slot port at 34. Box built for american bass xfl and needs more port area cause I get alot of port noise now. Wanna go with a wall at the c pillar and take the whole hatch. Goal is demo car. Good range but decent spl. Listen to rock when not showing but dubstep at carshows alot. Debate 4th or 6th. Skar says on site that the zvx isn't reccomended for sealed but when asked about a 4th they recommended 1.25 to 1.5 sealed and 40 inches of port area for ported section. The sealed sizes seem pretty small to me for such a large woofer tho.... but I have never done a 4th or 6th so I don't know..... ????

I’m not able to design right now

 

[Big_Dan_T]

I’m not able to design right now

Is there anyone you may reccomend? I can probably figure it out to do on my own but I don't really know the basics. I know to build a sealed section and then tune the ported section to the center bandwidth of the sealed. My software tells me the sealed side is 50 hz no matter how big or small I make it. If 2.5 - 3 sounds right and I could figure out how to understand that tuning, then I can design that and the sealed section on my own. I can't afford to build several boxes to figure it out so I wanna know what I'm doin before I start. If ya know what I mean. But if I can get someone that knows it well to design one for a reasonable price, I would know it is good.