How to design and build a 4th order bandpass enclosure

If you’re interested in building a 4th order enclosure and need some help, hopefully this page is for you. I have put together a bunch of tips and how-to’s that should help you put together a 4th order enclosure. Check it out.

There are 3 major steps you’ll need to do in order to design your enclosure.

1. Choose a Driver(s) – This would be the subwoofer – anything from a 6.5″ to a 18″ will do. You can even go smaller or larger. The most common would probably be 8″ and 10″ subs, due to the massive enclosure size of a 4th order bandpass enclosure. I currently have 4 10″ subs in a medium sized 4th order and it is roughly 17 cu/ft before displacements.

2. Choose a location for the driver. Is it for a home or a car? I assume most people will want it for a car, but they can be used anywhere really. Once you have a location you’ll need to measure the size of the area you’re working with. This will ultimately decide how many woofers and how large you can go.

3. Calculate total available area and choose what type of response you want. Do you want as much SPL as possible but at the same time creating a very peaky box or do you want a less peaky curve with the sacrifice of a few db? This will determine the ratio and size of your sections.

To determine the internal sq/ft you simply multiply length x width x height (in inches) then divide by 1,728. If you do 20″ x 20″ x 10″ for example you have 4,000″ then divide by 1,728 and you get 2.31 cu/ft, so that would be a pretty small box. If you have an non square area then you can break that up into 2 or 3 smaller square sections to make measuring simpler, then add the sections to get a total.

If you’re not super familiar with what a 4th order is, it’s basically just a sealed box and a ported box stuck together. The woofer is sandwiched in between and all of the sound output comes from a port. The 4th order design will yield a very large peak in spl at or near the tuning frequency, the width of the peak will depend on the ratio of the box. You can try different tuning frequencies in WinIsd or any box design program to see what it does to the response curve but on average 45hz is a safe bet for tuning. It allows the box to still dip into the 20’s on the low end while still having output around 60hz up top, giving it a fairly wide pass band. You don’t have to rune a 4th order super low to get into the 25-30hz territory like you would a normal ported box. The sealed section of the 4th order determines low end output for the most part, the larger you go the lower it will usually play but the port tuning frequency plays a role as well. If you tune higher than 45hz it will start to cut off some low end response. If you tune lower than 45hz it will then lose some upper end response.

I built my most recent 4th order very large on the sealed side, 1.0 cu/ft per 10″ sub. Then about 2.5 cu/ft each ported. This gives me 4 cu/ft sealed and 10 cu/ft ported total volume, since I used 4 subs. It plays under 30hz no problem. I went with a 2.5:1 ratio of ported to sealed which gives me a pretty good peak in output. It narrows the response a small amount but it’s not that big of a deal for me, I wanted the best output I could get with my budget woofers. You also need to remember to subtract the displacement of the woofers, any baffles or braces, and the port from any calculations you do.

The box ratio is simply the sealed airspace vs. the ported airspace, the ported side will almost always be the same size or larger than the sealed side. If you have a 1 cu/ft sealed section and a 1 cu/ft ported section, you have a 1:1 ratio, this will yield a more flat response but with less peak spl. If you have a 1 cu/ft sealed section and a 3 cu/ft ported section you’re at a 3:1 ratio, this will result in a  more peaky curve but the total spl will be higher. The average boxes you’ll see are usually 1:1 all the way up to 3:1. You will see some competition vehicles as much as 10:1 or more though with a very high tuning, this results in what is called a burp box. It will play one frequency really loud, the rest will be lacking severely. They are usually used for competition only. I like to have low bass too, so I built mine to play from about 28-65hz.

The port volume is calculated using the airspace of the ported section only. You calculate it the same way you do for a normal ported box. I use WinIsd to input my preferred response and tuning frequency with my given airspace and see if I can make that port length work. You want to make sure you have enough port surface area though, so you multiply the length times the width of the port,  for example a 12″ x 12″ port would be 144 sq/in. If you have 4 10″ subs which are about 300 sq/in of cone area (cone area chart at the bottom of the post) that port would be good sized since 144 is about half of 300. You can also divide the sq/in of port, 144sq/in in our example by the ported section of the box, we’ll use 10 cu/ft as an example. This gives us 14.4 sq/in of port per cu/ft of ported airspace. This is good enough. I try to shoot for 10-20 sq/in of port per cu/ft. If you go lower you may have port noise but if you’re limited you can try it, sometimes it works. You want to keep the port as close to square as possible, you don’t want a 15″ x 1″ port, it is too long and narrow with too much port velocity. If you do a rectangle port just make sure you’ve got a good amount of port width vs. port height.

You’ll see many people fire the woofers into the sealed section of the enclosure, I did this as well. In my case and the same as many others it is done so you can smell the voice coils if you begin the over heat them. I have gotten mine hot a few times and had to turn it down, if I hadn’t had them mounted this way, I probably wouldn’t have known it and fried a woofer.

In the construction aspect of the box you’re basically just building a large ported enclosure. The only difference being that the woofers are mounted inside of the box. You can do it in any fashion you want really, I built mine pretty simply as you can see below. You can see the full build by clicking here. You can build yours in any shape but squares/rectangles are easier to calculate, so keep that in mind.


Sealed section on the left and ported on the right. You have to make sure the woofers are all connected right or make one of the panels removable. I sealed the entire box up after mounting/connecting the woofers, so if something ever blows it will have to be cut open. I did test it all before sealing it up though, make sure you do the same unless you have a removable panel.

You’ll see some people put plexiglass/acrylic panels in, if I had the budget for that I might have done it. This allows you to access the woofers and looks cool. I did not brace my box much aside from the center panel. It is 2 sheets of 3/4″ MDF where the woofers mount. So that is a 1.5″ baffle in the box, it made it pretty solid. If I had massive power and stronger woofers I probably would have but for this setup I didn’t deem it necessary. You can also coat the box in fiberglass and resin for strength. Wooden dowels do not take up much air space but add a good amount of rigidity if mounted properly and glued or better yet fiberglass them in place.


I bolted my port in place, I could have probably used screws but I was originally going to make it removable. That plan changes though so it ended up being bolted in place. I sanded the edges of the port to round it over a small amount but a router would have been better. You can also kerf the edges but this is even more work, a lot of work. It can result in a small spl gain though, so if you have the tools and time it can be worth it. If you do kerf the port or round it over with a router you need to account for that in the length. The length will be measured from the half way point of the kerf or roundover. This usually adds only a small amount of length (1/2″ or so) but it will change the tuning frequency slightly (it will be slightly higher) if you do not account for it.

Hopefully this page has helped you on your quest to build a 4th order bandpass enclosure. If I missed anything or you have any questions feel free to drop a comment below.

Subwoofer Cone Area Chart (You can subtract a few percent for the surround, larger width surrounds taking up more cone area than smaller ones)

Single Sub

  • One 5.5″ = 24
  • One 6.5″ = 33
  • One 7″ = 38
  • One 8″ = 50.27
  • One 10″ = 78.54
  • One 12″ = 113.1
  • One 15″ = 176.71
  • One 18″ = 254.47


  • Two 8″ = 100.53
  • Two 10″ = 157.08
  • Two 12″ = 226.19
  • Two 15″ = 353.43
  • Two 18″ = 508.94

If you’ve got 4 woofers just double the amount listed under pair and so on for more.


  • brian says:

    Is the ported side always supposed to be the larger of the two Chambers and if not what is the result in doing this, just for insight…and if u were using 2 druvers in a 2 to 1 ratio is it the sum of the sealed area that represents the “1” or is it each individual sealed Chambers vol? As in 1cft x 2 sealed = 4 cubes ported or would it only be 2 cubes ported??

    • admin says:

      You can make it any ratio. The general rule is that 3:1 ported to sealed will give a nice bump at tuning frequency. The lower you go, the less of a bump. If you go 1:1 it won’t have nearly the peak, it can still sound fine but won’t be much louder in SPL than a proper ported box in many cases. 2:1 is the minimum I’d bother with myself.

      As for your box, I think I get what you are asking. If you have 2 subs that need 1 cu/ft total space sealed, you’d do 2 cu/ft ported for a 2:1 box. This is after port and woofer displacement, in a smaller box it is critical to account for it. If each sub needs 1 cu/ft sealed then just double the above. 2 cu/ft sealed section with a 4 cu/ft ported section, again only if each sub needed 1 cu/ft sealed.

  • Bradley says:

    Hello, I have an American bass hd12d2, & would like to use this box design. I have a Lincoln navigator and would like to stick with a single 12, running a fosgate t1500bdcp at 1 ohm to the sub. I was thinking 2cubes sealed with 5cubes ported. Does that sound correct? If so my next objective is figuring port size, design & location. Would you lend me a hand with this please? Thank you and I appreciate it.

    • admin says:

      I would go a little smaller sealed, you shouldn’t need more than 1.25 – 1.5 for a single 12 on the sealed side. You could leave the ported side big and get a massive output bump at tuning frequency. Port location will depend how your box fits in with the vehicles interior. You want it to fire cleanly and not directly into a wall. As for the port size it is easy, you just use the 5 cu/ft side of the ported box and tune it like one. A square port in a 4.75 cu/ft box (taking away woofer displacement) at 8 x 8 inches would need to be about 11.33″ long to be tuned to 45hz. That is what the average 4th order is tuned to, it will still get low.

      • chris patton says:

        OK I’m building 4th order box for two Alpine type r 10″s 3:1 ratio im lost on port i need 14 in port?? is this how deep port need to be??

        • admin says:

          I’m not sure what you mean. If someone says there is XX” of port they often refer to length but sometimes the surface area too. You need to know the height and width as well for tuning. 14″ is small though so whatever you read meant length most likely.

  • Artie Tyler AKA PAK-N PUNCH says:

    I have 8 ROCKFORD FOSGATE P210S4 subs and was told to put in FOURTH order and Im so Lost trying to configure them I have them in a 96 Tahoe firing up the boxs is ported and both subs and port fire up I’m metering at 141.7 on a 800a2 but want more and was told this one way to get it need input

    • admin says:

      Those subs have a qts of .43 according to this –

      That isn’t 100% ideal for a 4th order, the general rule of thumb is that you want a Qts of .50 or higher when considering a 4th order for subs. They would probably work but might not perform quite as well as some other subs. You could also try changing the tuning frequency of your current box along with the air space, which would be a lot less work. That might get you a few more DB on the meter depending how well it is tuned right now. You could also try more power, an 800a2 is only giving each sub about 100 watts and per the link above they can take double that. Doubling the power should add about 3db if the electrical can keep up. If you want a 4th order though for that peak output, I’d for with about 5.2 cu/ft sealed and 15.6 cu/ft ported. This would be a 3:1 ratio, giving a nice bump at tuning frequency which I’d suggest 45hz.

  • Rups says:

    hey guys need some help busy with a huge 4th order build using 10 x 12 inch woofer can you help me with sizes and port , need to tune around 37 to 40 hz

  • Nerros says:

    I’d like to build one of these enclosures for my garage, so space isn’t an issue. Im using a single Polk audio DXi104 SVC 10″ sub wired at 4 Ohms and would greatly appreciate your help.

    FS 35Hz
    Xmax Linear 0.622
    SD 54.25 in/2
    VAS .099 ft/3
    QTS 0.55
    QES 0.59
    QMS 9.1

    With a cut out diameter of 9 1/16″ (23.02cm)
    Top Mount depth 5 7/16″ (13.81cm)
    Bottom Mount depth 5 15/16″ (15.08cm)

    This is all new to me and I dont know what I like. I am assuming I like it loud and low.

    • admin says:

      Well, I’m not sure if this is good or bad news but I’d just suggest a normal ported box for that sub. If you want to build a 4th order you can but the specs I am getting just aren’t great. I can’t get the port big enough in surface area to be adequate without it being crazy long which won’t fit in that airspace. The best I can come up with is as follows.
      2:1 Ratio 4th order
      1cu/ft sealed and 2 cu/ft ported. Tuned to 45 hertz via a 4″ x 4″ square port which will be 18″ long. The port is on the small side so make sure to round the edges off to avoid noise as much as possible.

      The response is a few db higher from 35-60 hz over the ported box but that is higher bass notes. If you want more low end db you are better off with a large ported box for this sub. A 2.2 cu/ft box tuned to 30hz will yield more db from 23-34hz, which is the bulk of most “low bass” notes. That is a fairly large ported enclosure so the power handling will drop a bit but it will be crazy efficient even with low power. Good luck in whatever you decide to do. I’ve uploaded the graph (click here) which also compares a 1 cu/ft sealed box for that woofer.

      Also you gave me the wrong VAS, you added a zero. Luckily I caught it because the number seemed really off. I got the right one from Polk’s website. I left out a single digit in the past and ended up with a box tuned WAY off. Always triple check those numbers. 🙂

  • jose says:

    Alright im build a 4 order wall for 4 12 hds312 Max dem are h 35 w 50 d24 wondering if you could help me out thank you

    • admin says:

      That might not be enough space, from my quick math you’re looking at about 20cu/ft internal space. Take out the space for bracing, a large port, and the woofers and you are down to somewhere in the 15-17cu/ft area to work with. If you have 1.25 cu/ft for each woofer sealed that takes up 5 cu/ft. This leaves you about 10 cu/ft of ported space, so the max ratio you’d be able to do is 2:1 which isn’t going to give the massive bump that a 3:1 or 4:1 4th order would give. You could still build it this way but if you are going for max spl it might not be ideal. You could lower the sealed volume some and end up with a 3:1 but this will sacrifice some low end response. I’ll throw the T/S parameters from the website into a program later on and see what it shows, then I will edit this post. You might be best with a large ported box since you want 4 woofers in that space but we’ll have to see what the program says.

  • Jared says:

    Ok so I thought I had my box figured but I am once again stumped. I know all the equations and can get my box the right cubes to fit my space I am just missing one variable….. Airspace. My box is for two 15″s. It will be two ported chambers in the back (or ends) sharing one sealed chamber in the front center. The drivers will be facing the ported chambers. My speakers call for 2.5 cubes per for sealed box and 3.5 cubes per for ported box. Seeing as I am going for the most well rounded sound profile I am fine with the 5 cubes (2.5 per) on the sealed side since the sub backs face the sealed side as manufacturers specs. I just have no clue what ratio I should use to figure ported sides since the drivers are facing the ported chambers. Any ideas?

    • admin says:

      The standard size is 3:1 ratio, you can do 2:1 as well with slightly less output at tuning frequency or even 4:1 or 5:1 for extra output. So if your sealed side is 5 cu/ft total and you did the 3:1 ratio you want 15 cu/ft on the ported side. They need to be in one common ported chamber as well, otherwise it will be pretty much impossible to get the 2 ported chambers tuned exactly the same. You’ll then figure out your port size based on the 15 cu/ft section of the ported side only.

  • Pacco says:

    I have a pair of cheap 12″ eBay knock offs that I bought for a bit of nothing. I have zero t/s specs on this speaker. How can I determine if this will work in a 4th order box. Win isd gives me a grim outlook if I plug in numbers from other low quality speakers. Some boxes for a single 12 figure to be over 30 cu ft!! I can come up with approx 1.3 cu ft sealed and 3.1 ported in the space I want to use. I hope to use 3″ round ports. I have about 20 ft of heavy tube I can use in my boxes. Any advice?

    • Pacco says:

      In addition, the description does say it is a mid Q design. What mid range of QTS that is , I don’t know.

      • admin says:

        It is pretty hard to say or guess. You can buy a meter from partsexpress and it can measure the T/S parameters for you. If you only have 1.3cu/ft sealed and 3.1cu/ft ported total space there is no way that will work for a pair of 12’s in the 4th order. I would suggest at least 1-1.5cu/ft sealed and 3-4.5cu/ft ported per sub for an average 12″ that will work in a 4th order. So at minimum like 2cu/ft sealed and 6cu/ft ported plus you need to account for bracing, woofer and port displacement. So the box will be even bigger than that. You could try making a box for a single one of those 12’s and see how it is but plotting it will be impossible without t/s parameters. Good luck.

        • Pacco says:

          My apologies, a single 12 is what I planned to use in this space. In reference to port tuning, is it plausible to slide a port in and out while playing a frequency sweep to tune it. I am imagining that I would need to choose a port size, try it, then change to a different length, then yet again a different length….etc, etc. It seems to me that if I were to take a 8″ long 3″ round port and adjust the depth in and out, it would not change because the tube never actually changes. Is that correct? I have a good kicker that I finally took the time to repair. I believe that is what I will use this first time. I have made small bandpass boxes for 6.5″ woofers. When done correctly, and the cabin gain of a hatchback factors in, they get relatively good response in the 38-80 range.

          • admin says:

            You are correct, you’d need to change the length of the port to have a different tuning frequency. Sliding it in and out will change it a little because having it outside the box will change the displacement in the box some. However it won’t be a major effect. I would say a range of Mid 30’s to Mid 80’s should be achievable with a 6.5″ with a bit of experimenting. I’d try to start with 45-50hz as a benchmark and see where that gets you. It will peak here but should have decent output on each side of the curve to a certain point where it will fall off hard due to how 4th orders function.

  • Pacco says:

    I am running into an issue. WinISD is telling me to put the ports in the smaller of the two spaces. If I read your post correctly, your optimum ratio is 3:1. I understood that to be 1 sealed and 3 ported. I am using a kicker 05C124 comp 12. I am also wondering how much surface area difference there is when comparing the front and back of the cones. It has to be somewhat different. Is it simply not enough to be concerned about? One more thing. If I mount the sub facing the sealed box, am I supposed to reverse the phase?

    • admin says:

      WinISD will default the box to be a flat response, a lot of time that will end up with the box being oddly sized. Just adjust the size of the ported section so it’s the bigger one. I use the older WinISD, the newer one does not work well for 4th orders from what I tried/read. 3:1 is a pretty good ratio and a good starting point. Some people go lower for a more flat response such as 2:1 and some go as high as 10:1 for a crazy peaky output. I never even enter cone displacement, it shouldn’t have much affect on it either way. You don’t need to adjust polarity either way, some will try both ways as sometimes one will yield slightly better output but it depends on so many factors. The times it really counts are when you have multiple woofers mounted differently – some normal and some inverted. With a single woofer it isn’t as crucial. I had mine wired normally.

  • MONST1 says:


    i have 2 questions.


    where do you set your Lowpass filter? @ (24db and 18db slope)


    is it a good plan to put this Sub(Specs below) in a 1,06cf Sealed 2.12cf Ported @ 45hz Enclosure?

    QTS: 0,526
    VAS: 0.68405ft³
    FS; 39,9823hz
    RE: 2,2ohm
    QMS: 8,006
    QES: 0,563
    SPL: 86db
    BL: 17,24690T-m
    SD: 79,205inch²

    thanks 4 help and any answer :p

    • admin says:

      It depends on what I have for mid range and mid bass speakers when speaking on the crossovers. If I only had smaller mids around the 5.25″ and below range then I would go for 85-95hz. If I have 6-8″ mids then 75-85hz. I would say that is a good baseline to test from on the box size, that QTS should work well in a 4th order. The 2:1 ratio won’t give a killer peak but at the same time should be a fairly nice response range.

  • MONST1 says:

    ok thx i will try it:)

  • kicker guy says:

    I’m curious i usually do normal ported boxes but I kinda wanna try this…. I have a blow through box now so opening can be up to 49 wide and 17 tall and 8 foot bed can take it all up if needed…. I’m wanting to put 4 12s or 4 15s kicker l7 and I’ll be running off 2 1600.1 kicker amps or 2 2500.1 if the 15s…. Wat kinda space and port sizes would I need for these options? Really appreciate the help!!! 🙂

    • admin says:

      You would be better with 4 12’s. The 15’s would require a lot of space and with the limited height it just isn’t worth the trouble in that space but it could be done at like a 2:1 ratio box, maybe 2.5:1. 8-10 sealed, 16-22 ported cu/ft. The 4 12’s will work better, you have like 35 cu/ft or more of usable space from my estimates. I grabbed some random L712 t/s parameters, looks like about 6.5 cu/ft sealed, 19.5 cu/ft ported will work. That is a 3:1 ratio with a nice bump over a standard ported box from 28-61hz peaking around 43. That would be a 30 x 10 x 5.43″ port at 45 hertz. So 300″ of port area. All measurements internal btw. Add for bracing, port displacement, etc. Wood thickness.

      • kicker guy says:

        Is it best for subs to face into the sealed chamber like in ur pic or out? I’m going purely for spl numbers

        • admin says:

          The main reason to face them into the sealed portion is so the voice coils are exposed. It is very easy to over power and heat up subs in a bandpass. So you can smell the voice coils if they start to get stinky much sooner. If you have the subs facing into the ported section it will delay your ability to smell the woofers over heating. One isn’t better or worse as far as performance goes, some people do it for aesthetics as well.

          • kicker guy says:

            Questio.. I don’t have the program not sure which one ur using…. But would 2 15s fit in the same box udescribed for the 4 12s and sound right?

          • admin says:

            I am using Win ISD Click here to download it

            The box would not be the same. You’d need a different box for 15’s. It is very easy to figure though with the program. Just input the drivers T/S parameters into a new sub. Then get to playing, you can open numerous windows at once to compare how box size affects output.

          • kicker guy says:

            k so i downloaded the beta and pro…. pro actually gave me something useable but first time using this program…. here is wat it gave me it just dont sound right from wat im seeing….. told me that optimal was 8.414 sealed and 29.58 ported was optimal which is fine i can make that work its a 3.5 to 1 ratio but told me to tune it to 32 hz which peaks at 31 hz and f3 is at 20 hz and it says for a square port that it should only b 4×4 and 1.68inches deep which sounds like a tiny port from wat u told me earlier and wat i have seen of these kinda boxes they have huge ports…. am i doing something wrong or is this info correct?

          • admin says:

            You have to adjust the parameters it first shows you. That is just a baseline. You need to input the box size you are shooting for then check out the graph. It helps to open 3-5 different boxes so you can compare the curves as you make changes. You also need to manually adjust part of the port size. It defaults to 4×4 or whatever it is on each new box. It will not be ideal. You would want to start around 5 cu/ft sealed and 15 cu/ft ported as a 3:1 ratio baseline for a pair of 15’s in a 4th order. The port should be around 200 cu/in baseline – so 20″ x 10″ and see if the length is doable.

  • Phil says:

    I’ve read alot of the comments and questions on the 4th order box can’t believe how much space some guy’s are willing to give up for the box, like the one with 8x10s holy crap if you went 3:1 you’d be 8cf sealed sections & like 30cf ported sections. (I think, I’m new at this) That’s a whole Lotta space not to mention the extra weight 3/4 mdf isn’t the lightest wood, I guess you gotta be really hardcore to give up that kinda space for your bass.
    I may attempt one of these 4th orders for my 2 12 budget Infinitys I know my amps good enough as I recently blew my American Bass 10″Sub, it’s a Powerbass 2000.1d so at 2 ohms it’s rated for 1000watts (I think & 2000watts @1ohm) I just don’t have a ton of space to sacrifice. See what happens I guess it may be worth a try, thanks for all the calculations that was my issue.

  • Jeffrey says:

    Hello I need Help please. I have a jl audio 13w7AE and I contacted jl audio, so their recommendations for a 4th order is 0.90 cuft. sealed, 1.45 ported, area of port opening 50 square inches, effective port length 21.75 inches. Tuning 58 hz. The qts of this sub is .44. While this enclosure type is not the first choice recommended by jl audio, will this still sound good. I’m looking for a 50/50 sq/sql setup. Do bandpass boxes require the same amount of power as a sealed enclosure? Thanks for any help you can provide.

    • admin says:

      Normally I’d say stick to what the manufacturer suggests but that is a really odd box. With tuning that high you will lack a lot of low end response. You could give it a shot but it may not sound that great, you could try tuning it lower but I am sure JL would have suggested that if it worked with that woofer.

  • reru says:

    hello buddy need some help busy with a high spl car using this design i am look for a single peak hz like 73 hz , using very high ratio what should my sealed enclouse be to ported for 4 x 12 inch , also how big my port area should be , ts par are fs 42 hz qts 0.63 qes 0.71 vas 0.79

    thank you

    • admin says:

      You are really best downloading winisd and trying out some boxes for yourself, just add your sub to the database and make some boxes. You didn’t say is the vas was L or Cu/ft, I assume Cu/ft. I did some boxes and it’s gonna be real hard to tune to 73hz without having too much port. This is still too much but a box for those @ 70hz is as follows.

      4cu/ft sealed and 20cu/ft ported 5:1 ratio. You need to account for sub and port displacement too. Port would be 25″ x 35″ internally with a length of 1.63″. So it will be VERY short. This box also has NO low end at all. Strictly a high frequency burp box.
      Good luck.

  • danny griffin says:

    Im planning a 4th order for 2 ..jl audio 13w3v3-4 specs for ported are2.25 per sub couldyou help me with recomending cu ft per s and p port specs? Ive followed this feed for a few months seeing its the most resourcful ive found now im ready to build ..i got my ideas in mind id just really appreciate your helpfrom here ..this is my first 4th order bandpass ..thanks

    • admin says:

      You’ll need the T/s parameters to make a box. A basic starting point for a pair of 12’s would be about 3 cu/ft sealed, 9 cu/ft ported – tuned to 45hz.

  • Alex says:

    I’m figuire out a 4th order band pass for my 2001 Rockford fosgate power HX2 15″. Woofer specs are:
    Fs 22
    Qts .388
    Vas cu ft 4.45
    Xmax .74
    Spl 87.5
    Power handling 1000rms
    Speaker displacement .185
    Sealed cu vol 1.25
    Vented cu vol 3.5

    Would like for it to drop down into the low 20’s and go as high as about 55-60hz. Would prefer it to peak around 38-45hz

    • Alex says:

      What kind of volumes and port would you recommend?

      • admin says:

        You are really best downloading winisd and trying out some boxes for yourself, just add your sub to the database and make some boxes. You just need to input the Qes, Qts, Vas, FS, and SPL to get a proper plot line in the program. A good base line for a 15 is around 1.5 – 2 cu/ft sealed and 3-6 cu/ft ported. The response you want will be really tough though, low 20’s to 60 is a stretch for a 4th order. I mean it might hit all those notes but the lows and higher end will be significantly less db than the middle.

  • Eli says:

    To start off, Great article. We grew up making 4 order boxes but never really pay to much attention to port sizes. Now as an adult i stubbled across a 10″ FR HX2 RFD2210 for dirt cheap and thought what the heck. Have to admit its recharged my inter bass fever. i Picked up a kenwood-9102d in the deal as well so i am hoping this amp will fit this subs needs.
    With my available space where i want to install the box I am thinking the 2/1 ratio is my best bet. I want to build it in a long rectangle shape with .75 sealed and 1.5 ported.
    My question to you is, after reading your post, it appears my port size 3″ but you stated “make sure you’ve got a good amount of port width vs. port height.”
    What should be the depth in inches and the size of the port opening. Also what difference would it make if i made it rectangle instead of square?
    Also, i would prefer to put the port firing out the side of the ported side instead of the end. Will that make the difference?
    Your insight would help me out greatly.
    Thank you for your post. It has fueled my drive to see what i can get out of this hefty little sub.

    • admin says:

      If you use a round port you don’t need to worry about width/height. Port shape isn’t critical, some designs are just easier to fit in certain boxes. Just make sure to round the edges and keep turbulence to a minimum. You’d need to get the T/S parameters of your woofer and use winisd to design a box. You just create your woofer in the database. It will tell you what size your port needs to be based on the box size and tuning you choose. You can fire the port any direction really, just keep the woofer as far from it as you can. You don’t want it right next to the port. You box size is a good start for a 10″, you can open up 2-3 different boxes in the program and compare to curves also. Good luck.

  • gao says:

    Hey think for the information. I looking to build a 6th order and was wondering if you could help me. Sub I’m using is one 8 sundown e8v2 d2. Could you help check out my number? Seal side is .5 ported tune 33hz. Ported side is 1.5 tune to 65hz both after displacement. Also would recommend a 6th order vs 4th order for max SPL on music?


    • admin says:

      I once knew all about 6th orders but it’s been about 12 years since I last looked into them. So as much as I wish I could help, I sadly don’t remember enough to offer much advice. I know they can be insanely good, but it requires a lot of testing and tuning. The odds it is perfect out of the box are slim to none. They are very tricky but are cool boxes and fun to mess with. Good luck. I would say that would be a good baseline to start with though.

  • bowtie406 says:

    Can i three subs..hds312..share the same sealed area then each ported to three different tones? I have cargo area of work with. Im looking for spl…big dbs. Thanks in advanced for your input.

  • kenneth says:

    I have 2 t0d415 qes 0.57 and fs is 26.2 hz best design for this would be helpfull

  • blaza33 says:

    im doing 8 dd 2525s in a 2-1 my ported side is 26.5 how many sqare inches of port do i need for th 8 15s?

    • admin says:

      Well if you went with 15 cu/in port per cu/ft – you’d need about 397.5 sq/in of port. That is a 20 x 19.875 port.

  • Terry says:

    Hi, I’ve been using Winisd for a few days trying to come up with the best 4th order enclosure for 2 RE Audio SEX10d4 subs. I have gotten what looks like a good response from inputting 1.3 cu ft for the sealed and 2.3 cu ft for the ported. My question to you is when looking at the graph do I measure the response -3db to -3db or from what’s at 0db mark low to high. I plan to use a 6 inch round aeroport with some of it outside the box and pointing up through the factory sub location so I can get all the output into the cabin thanks for any advice you can give.

    • admin says:

      -3 to -3 is a range to look at. That is pretty much going to be what you’ll hear. You might hear some a bit lower and higher, they just be a lot quieter obviously since it falls off so quick on each end of the spectrum. You will still get some output past the -3 mark on each end, it just won’t be as substantial. Hopefully that helps.

  • Nate says:

    Good read. Im about to build a 4th for 12 fi sp4 15’s with 6 cresendo bc5500, one per pair, I planned on going 24ft3 sealed(2cubes per) and 48ft3 ported tuned at 45 hz. I love the lows and i like them loud. Does this sound like a good idea going 2cubes per sub? Or would you go higher? Also what would you recommend as to the ports square inches per cube on the ported side, should i go around 14 0r 20 per cube, bigger or smaller?And my last question would I be better off building all the subs on one wall(like yours so youd see them all when you look in) or separating them with 6 on the left and 6 on the right or a horizontal v? I do plan on keeping the shape of the port as square as possible. THANKS FOR YOUR HELP.
    DUAL 1
    Fs: 27.6 Hz
    Re: 0.65 Ohms/coil
    Qms: 6.56
    Qes: .52
    Qts: .48
    Mms: 434g
    Cms: 0.77mm/N
    Sd: 810cm^2
    Vas: 70.4 l
    Spl: 86.4dB 1W/1m
    Bl: 13.7 N/A
    Xmax: 33mm
    Rms: 3000W
    Sealed box: 2-3.5cuft
    Ported box: 3-5cuft
    Mounting depth: 11.250”
    Displacement: 0.21cuft

    • admin says:

      That box sounds great. I would go with that, it should get down. As for the subs, a lot of times for me I just build what I can fit. Once you mock it up, you might be stuck one way. If you do a V, try to keep the woofers as far apart as you can. It is possible to get a gain when you do a V, but it’s a lot of complicated math. It’s best to just go for it if that is all you can do. If not I do flat for simplicity sake. I would stick to around 15 per cube on the port myself, I think you’ll end up with a truck sized port otherwise. Good luck. If I missed anything let me know.

  • Nate says:

    Which is a better set up, subs on wall when you look in like yours or subs on the left and or right when you look in, also what is your recommendations as far as port area to box ratio for best low frequency output, and is 2cubes per 15 sealed a good number?

  • Anthony says:

    Ok so im doing this for my home i have 1 15 dj sub no enclosure will be running 1 500 watt dayton audio amp plate whats the best way to do this i know its gonna be big but for mobies i want that shit to be nasty thanks in afvance

  • ricky says:

    Hi I am in the process of building my 4 order
    My box size is
    38″ wide at the top
    50″ wide in the middle
    38″ wide at the bottom
    37″ depth
    33″ high

    I have 4 x15″ ground zero 3000rms each
    What I need to know is what distance do I need to mount the subs from the back wall and what size port do I need to have to get the correct spl

  • joshua says:

    I’m building a 4th order for a SSA xcon 15″. Should I 1:1 or 2:1 for SQL setup. Would be running 1500w daily and 2000w for bragging rights.
    Amp AQ 2200
    Sub xcon 15″ 1750w rms
    Space is 5-6 cubic ft available
    I’m building a 4th order for a SSA xcon 15″. Should I 1:1 or 2:1 for SQL setup. Would be running 1500w daily and 2000w for bragging rights.
    Amp AQ 2200
    Sub xcon 15″ 1750w rms
    Space is 5-6 cubic ft available
    Max specs. w40″ X h24″ X d34″

    Enclosure Recommendations:

    Sealed: 2.0 – 2.25 cu.ft.
    Sealed: 2.75 – 3.0 cu.ft. optimal
    Ported: 3.0 – 3.25 cu.ft. @ 26-33 hz
    Ported: 4.0 cu.ft. @ 26-33hz opt.
    Sub Outside Dia.: 15.625”
    Cut Inside Dia.: 14.125”
    Displacement: 0.20 cu.ft.
    T/S Specs:

    Re: 3.7
    Fs: 31.3
    Qms: 6.11
    Qes: .45
    Qts: .42
    Mms: 268g
    Vas: 88.4 L
    Sd: 810
    BL: 20.71
    SPL: 89.6 1w/1m
    Xmax: 31mm

  • erns says:

    Hi thx for the link gave me good insight to my build im thinking of doing if u can drop me a email plz I have a couple of ideas I want to run by u I wana try and build a 4th order wall in my 1995 hyundai accent sedan with 4 15 inch subs I would like ur wise council in this matter thank you so much

  • Jake says:

    I have 2 PSI Platform 3 18s.
    With a 2:1 3cu.ft sealed and 6 cu.ft ported.
    Would this be sufficient enough? Would it still hit the lows?

    Also I see people have port and some not. Some people just have a big cut out rectangle or square but with no extended port walls. Please explain the differ between the two.

    • admin says:

      Sorry for the late reply – I would check with PSI regarding the box. I am not sure on the requirements for those subs. It does sound a bit small for 2 18’s. As for the box – they are all ported when they are 4th orders. The ones that are short are designed that way. It may just seem like a hole but the port is just designed in such a way it only needs to be 2″ deep sometimes due to the high tuning frequency of 4th order enclosures. So it’s just a matter of port tuning and design.

  • Jason walters says:

    Hi there I am very interested by your designs and I would like to build a box using this design. I am using 2×12″ tagra xxx 4d ,dual 2 ohm subwoofers and 2×2500 watt 1 ohm tagra amplifiers (all south African built) and would love some help with measurements, volumes, ports etc I am looking for high spl as well as good every day sound

    • admin says:

      I don’t have time to do box designs at the moment, so sorry. I wish I did. If you just follow all the directions and use the program WinISD it isn’t that hard. If you have specific questions I could try to help but building plans from scratch is a lot of work.

  • Joshua says:

    I have see a few different 4th order designs. some like yours and some that have two sealed chambers on each side of the box sharing the same ported area. How does this effect performance and sound?

    Also what causes some designs to be more sensitive and “unload” the subs when someone opens the doors to the car while playing?

    Last, I wanted a 4th order for 2 15’s Sp4’s. I want to play lowww like in the 20’s. don’t really care much about the higher notes some maybe 3.5:1??. and will a bigger port area cause more air movement?

    Fs: 27.6 Hz
    Re: 0.65 Ohms/coil
    Qms: 6.56
    Qes: .52
    Qts: .48
    Mms: 434g
    Cms: 0.77mm/N
    Sd: 810cm^2
    Vas: 70.4 l
    Spl: 86.4dB 1W/1m
    Bl: 13.7 N/A
    Xmax: 33mm
    Rms: 3000W

  • Alex says:

    I have a JL Audio 10W0v2-4 12″ and i’m looking to build a nice box for it. Any recomendations. Im new to this!

    • admin says:

      Do a lot of research, do it right the first time. 🙂 Sorry I can’t design the box for you, wish I could. Just short on time currently.

  • Mark Cline says:

    I hqve 2 15″ kicker cvrs and the sealed ranges from 3-5cu ft.woulddoing the sealed side at 10cu. Ft. Port side at 30 cu ft give me a god spl and if so can u help ne with the port

    • admin says:

      Yes, that would be crazy efficient. I can’t do formulas at the moment though, so sorry. If you ask on some car audio forums maybe someone can do the port calculations for you on WinISD. It’s a free program. 🙂 Good luck.

  • derrek says:

    Hey man I have two 15 inch db drive platinums im totally clueless on how to do tjos man i wanna build a nice 4th order for them but dont know wtf im doing like dimensions

    • admin says:

      I would suggest reading up on basic sealed box design. Make a standard 1 cu/ft box with the internal measurements of 12 x 12 x 12. You could buy a cheap 8″ sub to mess with. Then once you have made a basic box, move onto the more complex one. It would be really hard to make a 4th order your first box.

  • ken says:

    Hey bro have u ever heard a 4th and it sounds great at low volume but as soon as u crank it sounds like wood is vibrating or the subs fighting

  • Brady Strong says:

    I need some help. I’m planning on a build for 6 sa 15s and would like to see possibly a 3:1 ratio tuned around 45hz. Help would be greatly appreciated.

    • admin says:

      I assume you probably got an answer by now, been a while since I checked this post. A good base line per 15 is 1.5 – 2.5 sealed and 3 – 7 cu/ft ported. So for 6 you’re gonna need an entire truck bed or Suburban type SUV.

  • Jamie says:

    Hi I’m looking at building a 4th order or even 6th I have 2 15″ ‘re sx pro’s just wondering how big the box should be I go in to spl comps and need load as I’ll be running 3000rms to them if you could help it would be great thanks

    • admin says:

      I would try a base line of 3-4 cu/ft sealed and 6-12cu/ft ported. That is going to be a massive box though, so get the measurements and triple check them.

  • db xtc says:

    I’m running an 18″ sub in a power limited class of 1000W. Is it feasible to run a tiny sealed side (like 1.25cf) and 4-6cf on ported? I have limited space to work with only concerned with spl at burp freq.

    Would I lose potential spl in a smaller box? I burp at 51-53hz.

    • admin says:

      You could but there are so many variables it’s hard to say. I would try what you said and go from there. I think 1.25 should be good especially burping that high.

  • Chris DeWitt says:

    I keep hearing all this about 4th order boxes. This is new to me but i know its been around for a while. I am running 2 Crossfire C7 12D1s. I was thinking of trying a 4th order box. Would this kinda box fit into a mitz. Lancer trunk? Is so what would u recommend for cubic ft sealed and ported sides and port specs

    • admin says:

      That has a pretty small trunk, I think you could do a 4th order for 1 12″ but not two. A good way to think of it is – could you fit a sealed and ported box for each 12 in the trunk.

  • mike says:

    I am designing a 4th order box for 2 DD sw6.5 subs and would like to keep the low end above 34hz. It will be a 2:1 box at .67cuft to 1.35cuft with 2 3in round ports. 11.7in long will be at 45hz with my math witch is were I have tuned all my 4th orders to so if I tone to like 55hz (7.13in long) will that keep me out of the 20hzs range. The subs don’t like to go that low without kissing the back plate.

    • admin says:

      If you play a 20hz tone the speaker will still try to do it. The box merely tunes the sound to your liking, it can’t change what the speaker receives. So even if you tune higher it can still attempt the low notes and have the problem you mentioned. If you are worried about bottoming out on low frequencies I would suggest a sub sonic filter set at like 30hz with at least an 18db/octave cutoff.

  • curtis p says:

    hi im building a 4th order box for the back of a 2000 jimmy with 4 type r 12s the original ridged rubber any advice on dimensions and port size . also in the sealed side should i individually seal the subs or as a group? im looking for a flat base response as i listen to a variety of bass music. thanks in advance

  • Christian says:

    I want to do a 4th order design for 2 l7 8s. I want them to be as loud as possible but I want them to be able to play 30 hz without bottoming out, but I still want them to be able to play highs. What do you suggest?

  • steven says:

    Got two planet audio z10 subs. Cant find anything on specs for these. Can u help. Thanx in advance

  • joe says:

    Hello I seen most of the comments I’m wanting to build a 4th order box for a single sa-12 I have is there any words of advice or help you can give me? Also do you know any links with dimensions or diagrams for building a box like that?

  • R Gomez says:

    Hello, I’m looking for some basic specs on a 4th order bandpass box for 1 Sundown Audio Ev12 (Fs: 35.8 hz Qes: 0.56 Qms: 6.79 Qts: 0.52 Le: 1.85mH Vas: 47.6L) I am looking to bulid a 2.5:1 ratio enclosure for the trunk of a Lexus IS250. Could you recommend Air Space and Port size (square port). I am considering making the rear chamber .75-1.0 cu ft and the front chamber 2.0 -2.5 cu ft. As for the port I’m really not sure, was thinking maybe a 4″ or 5″ by 8″ diameter. Length is the big question. Any help would be much appreciated.

  • Joe Padilla says:

    I have a jl 12w7 and I have been told a 4th order box is what I need to get deeper bad but not too sure on how to do it as I have never built a box before but I’m handy with woodwork. Any suggestions on what specs I should use for it? Any advice is appreciated. Thanks in advance.

  • Cameron Scott says:

    Hi! I’m looking to build a box for 4 FI SP4 18’s, and I need some help with the box dimensions for a fourth order

  • ralph says:

    I’m curious, I have two alpine type r 15’s in a 4th order band pass, being a novice box builder, I read your article and found that my sealed portion is 7 cubic ft with a potted section of 3.5 cubic ft, I hit lows with a span of 20hz -45z I have this built in a 2 door Pontiac grandam, why is the internal volume of the cars cabin not also considered as an order or port?

  • Rick says:

    Hi… I am plannig on doing this box. i have 4 kicker 12″ CVR dual 4 ohm vc.
    what would my box need to be like?
    How do you calculate port length?
    I have Lincoln town car… plenty of trunk space. the main opening is square.
    then the upper shelf that can also be used is 40w x9t x 15d.
    The subs can go in one box with 4 individual chambers.. 20x12x10. that would put me at 1.38 cu ft.per sub. I would then have an Lshapped upper chamber .. the front shelf area of 40x9x15=3.125 cuft. then the top of the subs connected to the L (basically i just used measurements in nice square….) the other half would yield me 5.902 cuft.
    That would put me right at 9 cu ft …ported above the sealed 5.52…
    Would this work and be good…I can make the sealed camber smaller to get to the 2:1 ratio… How big is the port…. I want it to come right up thru my rear deck…
    I know this was a lot.. but I hope it helps and you can help me… This would be just a big L shaped box….

  • Emerson Hammacher says:

    Hello, I would like to build a band pass box 4 ° order for my subwoofer pioneer TS-W3003 12 inch, but I have many doubts and I would like your help to make this construction. The subwoofer data are below:
    Fs (hz) – 35
    Range frequenc – 20hz to 80hz
    Qms – 11.50
    Qes – 0.62
    Qts – 0.59
    Xmax – 0.54
    RMS Continuous – 600


  • Emerson says:

    Hello, I would like to build a bandpass box 4th order for my subwoofer Pioneer TS-W3003D4 12 inch, but have some doubts as to the subwoofer manual calls for 16 liters to the sealed compartment and 98 liters for the ported enclosure. I would appreciate your help and opinion on the measures of each compartment and the Port size (square port).

    Below is the subwoofer parameters Pioneer TS-W3003D4 12 inch:
    Fs: 35 Hz
    Frequency response: 20 Hz to 80 Hz
    Qms: 11.50
    Qes: 0.62
    Qts: 0.59
    Mms: 257g
    Vas: 34.6 liters
    Spl: 96dB 1W/1m
    Xmax: 13.8mm
    Rms: 600W


  • tim vosselmann says:

    I was wandering if I could build a forth order using a round port instead of using a square port? I mean a forth order 12 cubic ft in the ported side with an 18 inch diameter round port.

  • ely smith says:

    am building a 4th order with four 12s I just wanted to know about port area
    doing 2;5;1 I like lots of spl you said half of my cone area so if I do 200 inches
    of port ft is that ok my port side is 10.2 net that will be about 19 iches of port
    will that be ok that’s with in the 10-20 inches thanks.

  • JMehoff says:

    I am building a 4th order thats going into the back of a 2 door Jeep cherokee. I have all the room i need up to 20+cuft. I’m going to use 2 Soundqubed HDS15’s at 1 ohm with a AQ4500.1, Singer 320A Alt and 4 XS3400 Batts.. so Beefy electrical.

    F(s) 35.66 Hz
    Q(ms) 7.836
    Q(es) 0.927
    Q(ts) 0.829
    Sensitivity 1W/1m 86.33 1W/1m
    BL 25.20
    Xmax 14mm
    RMS 1200W
    Peak 2400W

    I’m wanting a good daily pounder, something thats going to play GOOD highs and GOOD lows. I cant stand muddy bass. I’ve spent alot more on my mids and highs than my lows because i want LOUD but clean as hell. If you can let me know what you think about the HDS15s for this. i havent purchased them yet because i need to make sure this is going to work. i already have the Alt, Batts and SQ4500.1 though.

    Thanks, Jack

    • admin says:

      With the right port tuning I am sure you will be happy with a setup as bad ass as that. I have not used SQ stuff myself but from what I’ve seen most users seem pleased with the equipment. Good luck with the build.

  • Milan Sagar says:

    This is the woofer & i will be using the two of them, can admin please help me out with the dimensions for a 4th order bandpass.

    NVX VC-Series Subwoofer Specifications:
    15″ Dual 2-ohm VC-Series Car Subwoofer
    Power Handling:
    RMS Power Range: 850-1000 watts
    Impedance: Dual 2 ohms
    Pressed paper cone with woven fiber top
    High excursion foam surround
    Cast aluminum basket for maximum rigidity
    Dual Poly-Cotton Spiders
    3″ Aluminum Voice coil
    195oz. Triple stacked Ferite magnet motor structure with protective rubber boot
    Sensitivity: 87dB
    Frequency response: 20-220 Hz
    Resonance Frequency (Fs): 24 Hz
    Total Speaker Q Value (Qts): 0.36
    Electrical Q Value (Qes): 0.409
    Electrical Resistance of Voice Coil (Re): 3.20 ohms
    Mechanical Q Value (Qms): 2.910
    Optimal sealed box volume: 1.50 cubic feet tuned at 40 Hz
    Optimal ported box volume: 2.50 cubic feet tuned at 33 Hz
    Top-mount depth: 7-9/16″

    • admin says:

      Sorry for the late reply but the PC I had my box building software on is dead. I assume you’ve gotten it figured by now anyway. If not you can start with the suggested sealed volume of 1.5 sealed, then use 3.0 ported for a 2:1 or 4.5 ported for a 3:1 – this is per sub. Then use the program I have linked in the post for the port sizing.

  • ash says:

    I Am new to this forum, i got a home theatre onkyo amp with passive subwoofer which goes down to 30hz but I am not happy with the performance. Its Not powerful sub at all. I Want to build my own 4th order sub, i got 10 inches driver of pioneer which reach 20hz as per the company specs. now i am lost how shall i built the 4th order which can reach down to 20hz because its mainly for movies.
    Please help me with measurements in fact i want a good response from 60 to 20hz.
    Thanks & Regards

    • admin says:

      Sorry for the late reply but the PC I had my box building software on is dead. I assume you’ve gotten it figured by now anyway. I will add that in a home the frequency response is much different than a car. A basic ported box tuned low is usually plenty for a home setup. Good luck either way.

  • Robert says:

    Can you please help me with my 4th order BLOW THROUGH ( 2003 TOYOTA TACOMA DOUBLE CAB) for 2 sundown audio X 10’s rev 1 dual 4 ohm I currently am building on but am lost on the port size and length I am going for a 3 :1 ratio and have right now 1.75 sealed common chamber (cone side) and 5.25 cubes ported after displacement ( each sub is .21) I want the low lows and best output ..
    box right now is half put together
    external dimensions are 15 tall 41 wide and 29 inches depth
    Internal port chamber dementions 13.5 tall 39 wide and 20.25 and left room for port and port wal, 45’s
    internal sealed dementions are 13.5 tall 39 wide and 5.75 depth
    I have alot of mixed information on port size and length
    amp : sundown audio scv 4000d
    Singer 250

    • robert says:

      Ts pramaters for the 2 sundown audio x 10’s rev 1 dual 4 ohm are
      fms 29.8
      res 103.4
      re 6.1
      qms 5.37
      qes 0.54
      qts 0.49
      rms 10.5
      cms 0.09
      mms 300.3
      bi 25.1
      spl 81.2
      vas 17.5
      le 4.04
      lp 64.4
      cp 589.0
      rp 56.1

    • admin says:

      Sorry for the late reply but the PC I had my box building software on is dead. I assume you’ve gotten it figured by now anyway.

  • Cesar says:

    For an 18″ subwoofer, what would be the rule of thumb for the sealed side? 3cf? I’m doing a 2/1 ratio just wondering what would be a good size for the sealed side of the 18″ driver. Thanks.

  • Frans says:

    Heey first off all, this is a nice article

    I have build a 4th orderfor my 6x 12inch of esx Qe 1224
    The closed box is 210,6 Liter and the ported side is 430 liter
    I have 1 port ( 30cm high 50cm weight and 27 cm long ) thats arround the 44-47 hz , and 1other port of 19 cm x 35cm x 35cm ik peaks at 39hz 149,6db thats way to low db

    I wanne push to the maximum out of the subs please can you help me i wanne tune it between the 28 and the 55 hz

    • admin says:

      I would stick to one large port. I am not on the metric system so your numbers don’t translate for me but either way you must just use one port. Mixing port sizes rarely ever helps anything. I’d stick to a 45hz baseline tune.

  • tony says:

    current my box is being constructed with a 2.5-1 with 4 cubes ported but i am running in to a issue trying to figure the port being blow thru rear deck i have a space of about 10″x8″ with a overall height from rear deck to box floor of 22″ but not sure how long to make the port for tuning

  • Bill says:

    I have a DC Audio M3 8″ 600rms 1200peak I’m gonna power it at 1ohm with a DC audio 1.2k , is there any like guidance you could give me? Last time I built a box was 12 years ago lol haven’t messed with anything since I’d really like to do it myself but I’m having a hard time understanding all this 4th order stuff , much apriciated

    • admin says:

      You could always start with a simpler ported box to get back in the swing of things. Then read up more on 4th orders and do that one after you had a bit of practice on the ported. It’s basically like making a sealed and ported box in one with some math on the side.

  • cesar says:

    hi I need help for a 4th order for my pair of alpine type R 12 ” (swr – 12d4) for explorer 1998 4-door , with a source of 2500 rms a 1 ohm.

    what is more necesitto the port size

    I would like a ratio of 3: 1 to raise more db.


  • Cesar says:

    What’s the recommended volume for an 18″ subwoofer sealed side on a 4th order? I asked here before but didn’t receive a reply. Hoping this time I get an answer.

    • admin says:

      It would depend entirely on the sub and space available. There is no set answer based on speaker size. A good start when working on box calculations would be 2 – 2.5 cu/ft.

  • Jayson Christensen says:

    i have 2 skar audio zvx 15’s i’m looking at a 2:1 4th order in my 97 yukon, what would my port be if tuned to 45hz?

  • Billy Brigg says:

    I have a 4th, for 2-crossfire c7- 18’s. The sealed side is 3.5 (subs firing down into sealed side) and the ported side after displacements is 12.9.

    How would I calculate the port size and depth to be tuned at 45hz? One calculator I found showed it being 12″ x 12″ x 5″ but I don’t know if that is correct.

  • akuma says:

    Hey, should the tuning frequency be determined by the cars resonant frequency? Or does that not matter? I was told my car has a 55hz resonant freq so the 4th tuning should be a few hz below that – 52hz. Is this true? Or should I still stick with 45hz as my tuning frequency? Also if I do 52hz what bandwidth range would I be hitting?

    Secondly, the port direction. If the port is facing up thru the rear deck vs forward thru the hole when the seats are down. Will this result in a different sound or will it sound relatively the same? If it won’t sound the same what difference would I hear vs port aiming top to port aiming forward??

    Finally, I was told 4ths are not musical at all and mainly used for spl purposes and don’t make music sound good for everyday listening, is this true? If so, how do u make it more musical but loud at the same time? Also – I was told 4ths don’t work well in coupes but better in sUvs and trucks and sedans. Is this true as well??

    Thanks for your help

    • admin says:

      You can tune to the resonant frequency to get the peak DB but you will lose a lot of low end tuning that high. Unless you plan to compete I would stick to the 42-47 range. The direction the port fires can affect sound but it isn’t a huge deal. Often I do what is easiest and works the best in a given setup. Aiming it through the rear deck would likely cause more rattles too. You can put a 4th order in anything, vehicle doesn’t matter. However they are indeed not very musical, they are extremely peaky enclosures. Some songs will have much more bass than others. You can tune it 1:1 ratio to make it less peaky but that sort of defeats the purpose of a 4th order which is SPL. If you want clean sound that isn’t too peaky then a nicely tuned ported enclosure may be best.

  • joe says:

    hello i have a sundown x 12 on a twisted sounds 1.3k i would love to do a 4th order and i would love to play down to 18hz and probably up tp 40hz or 38hz any input will be help full thanks

  • JP says:

    Hi, could you help me choose a driver for a specific applicaton?
    I want to build an underground outdoor subwoofer (4th order bandpass) like this one:
    This a 12″, but i’m open for 15″.
    The amp wil be my rotel, who give 2x150W RMS @ 8ohms so a DVC 8ohms would be the best.
    A marine sub or car subs with polypropylene cone and rubber surround is needed.
    Any advice on a driver for this specific setup?


  • Oscar says:

    thanks for the write-up man! i learned a lot here.

    i have 8 american bass vfl8d4 8inch subs. planning to build a 2:1 4th order bandpass. 4 cu.ft sealed and 8cu.ft ported giving each sub 0.5cu.ft sealed and 1cu.ft ported. will be tuning the port at 45hz as you said is a safe bet. is my ratio ok? or should i go for 2cu.ft ported and 1cu.ft sealed each sub? that will be 8cu.ft sealed anf 16cu.ft ported total. will be powering them with taramps 8k. hope to hear from you soon. 🙂

    • admin says:

      It sounds like you have a great plan, I’d go with that for sure. If anything you could go 0.5 and 1.5 but don’t make the sealed side 1 cu/ft per sub for 8’s. That is too big.

  • Gohil Jatin says:

    Hey admin. Its really nice information for me. Planning to make a 8″ sub box with this calculations. Hope this will work finest for me. Thanks a lot friend for this information.

  • Al says:

    Great write up , I have a question about funded my vent length. I am running 2 AB Xfl 15s and I plan on having roughly 6 cubes on the sealed end and 12 cubes on the vented. I will have about 175 Sq inches for the vent but not sure of the depth. I would like to achieve 45-50 on the high end. Is there a site or calculator to assist me with this. Once again great write up and thanks for your time

  • William Taylor says:

    I have an American bass XFL 1522. It will be going in the trunk of a Grand Marquis so space is not an issue. What do you recommend I do for this?

    • William Taylor says:

      This will be for daily listening not comp burp or anything like that. I had it in a cheap ass obcon box and it blew it apart. Time to build my own. I’m dying to try a 4th order.

  • William Taylor says:

    I plan to build one for a XFL1522 can you give me an idea on box dimensions? My trunk is plenty big enough, I have a Mercury Grand Marquis.

  • cj says:

    could someone give me a rough measurement on one of these boxes for a single kicker solo 15 i have plenty of space

  • big bass says:

    ive got 2 orion hcca 15s the maximum size of my fourth order enclosure can be is a 1:1 ratio to fit behind my 2005 chevy colorado extended cab seat. ive done the math and both my sealed and ported boxes will have 11 cubic feet total of 22 put together 53L x 38H x 19W. i want the low end response mostly , around 22-28 hz thats why i designed it big on the sealed end 5.5 cubic feet per subwoofer. if you have any additional info that you think would be useful let me know.

  • Jacob cooper says:

    Hello I’m terrible at ports and I’m building a 3:1 4 cu sealed 12cu ported for a single droppin hz hotel 18 and I was wondering what your advice on port size would be as far as depth mostly

  • Arnett Pierce says:

    I have two 12-inch UPA speakers are 1500 watts RMS I’m trying to build a 4th Order Box but it keep cracking the Box do anybody have any ideas that can help me with a boss 2 12 UPA speakers can you please send me a design with a 4th order so I can get this going on

  • Jay Rock's Mtx says:

    How about for the mix ts8512-44 (4ohm dvc)
    Using 2 of these with 2 Hifonics 2000d dual mono amps.
    BEST sealed was said to be 1.25 cu. ft. Per chamber.
    BEST ported was said to be 1.75 cu. ft. Per chamber.

    As to both SUBS on a blow thru 4th,
    That would be multiplied by 1.5
    If both were thru same port ?

    The port can be adjustable if it slides in and out with a trim piece that you can screw port to adjusted length.

  • Antoni says:

    What ratio do you recommend for 2 HDC3 18’s in a 4th order and how large of a port is needed. I have about 33″ h x 54″ w x 30″ d space to work with. Also what tuning frequency is best to tune the port. Any help would be appreciated. Thanks!


    hi ,I am using 4 x DD815s running off a taramp 8000.need sum guidance on designing a 4th order for upper 45hz to play loud and clear ,not low bass.

  • Jacob Seibert says:

    Looking to build a 4th order box for a pair of pioneer ts-w3002d2 subs the box will be in the trunk of a chrysler 300 I entered the parameters into winisd but keep getting tiny volumes… any advice for values or for box design in general?

  • alex says:

    Hey. I need help in calculating the box. I have 2 15 sub. Here is their description
    Re = 3.9380 ohms
    Fs = 26.7755 Hz
    Zmax = 35.6960 ohms
    Qes = 0.5415
    Qms = 4.3666
    Qts = 0.4817
    Le = 5.0207 mH (at 1 kHz)
    Diam = 317.0000 mm
    Sd = 78923.8736 mm ^ 2 ()
    Vas = 4.3109 cu. Ft
    BL = 17.78
    Mms = 255.7221 g
    Cms = 138.1643 uM / N
    Kms = 7237.7578 N / M
    Rms = 9.8524 R mechanical
    Efficiency = 0.4073%
    Sensitivity = 88.1168 dB @ 1W / 1m
    Sensitivity = 91.1949 dB @ 2.83Vrms / 1m

    I use the WinISD program and have the following parameters: closed camera 4.6 cu.ft. ported camera 12.7 cu.ft. And setting port 45Hz. The port sizes I use are 2 10 inch tubing, their length is 8 inches.
    All is well or that it should be changed? I want to have more volume at 28-35Hz
    With patience to wait for your answer.

  • Ian Madvig says:


    I am trying to figure out my box for 1 Skar ZVX-15v2. I am planning on going with a 3:1. So my dimensions are 4ft3 sealed and 12ft3 ported. I am not confident that my port size and length are accurate. Could you tell me if this box will be good and what size and length I should use for the port. I would greatly appreciate any help as I have done so much reading and just can’t seem to come up with the port info on my own. I look forward to hearing back from you.

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