4th order bandpass boxes

I used WinISD alpha software to design a 4th order bandpass box... I've got the results on paper what I want but the tuned freqencies between the chambers is 16Hz apart... will this be a problem? The front chamber will have 2x 12" by 4" by 5" slot ports OR 6x 4" diameter x 5.92" vents. My main question is, will the difference of frequency between the chambers make the box not work? because it looks great on paper. Also the program takes into account vent end correction. If im just using pvc piping what alignment should I use?

did you find the tuning frequency per chamber or for the box as a whole?

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what do you mean 16Hz apart??

a 4th order bandpass only has ONE tuning frequency

The rear chamber or "sealed" part is tuned 16Hz lower than the front "vented" chamber which is tuned at 80Hz. The graph doesn't look like your typical 4th order graph but it does reflect what I would like to get out of my subs based on the music I listen to.

a sealed chamber cannot have a tuning frequency as there is no port to tune

i think you accidentally chose the 6th order bandpass...which in WinISD is a parallel tuned bandpass model

I know what you mean but the chamber is tuned, not manually of course because there is no vent to adjust but by the amount of air space you give the chamber.

so, do you mean that the rear chamber has an F3 of 16Hz? sounds odd to me as it would have to be very large. What is the reasoning for deciding to go with a BP, vs. a slot port or sealed?

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used to be loud, used to be fast...now I am married LOL

man... read my posts. the rear chamber is 64hz, and the front chamber with the port is 80hz, together the box as a whole will generate some mean notes as long as theres not something I don't know about yet... plus I've built plenty of plain sealed and vented and I want to step it up. So if anyone has built these in the past and has some good tips I'd like to know them.

Also, to hopefully rid the box of the noise above 120hz typical of bandpass boxes does anyone know where I can get low passes that go inline with the rca cables for cheap? I know crutchfield has them but they're 20 a pair.

I think you don't know what you are talking about

4th order boxes are only single reflex...meaning only one ported chamber.

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1           1   <-- this (sealed) chamber has a frequency
1    64Hz   1       inherent to its air volume
1           1
1---Sub-----1
1           1   <-- this chamber with its vent also has a frequency
1     -------       due to the air volume of its chamber + vent air
1     -------       volume
1 80Hz     1
1-----------1   They are at different frequencies. Is this ok?

Im gettin tired of messin with it anyway, the bass reflex design is only about 8-10 db higher than that of a plain sealed chamber.

holdinmyown wrote: the bass reflex design is only about 8-10 db higher than that of a plain sealed chamber.

Only? 8-10dB's is dramatic!

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2013 Kia Rio -90a alternator
DDX470HD GTO14001 GTO1014D (x3)
Big3 in 1/0G
1/0G to GTO14001

That is, if you know what you're talking about. It doesn't seem like you do, though.

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2013 Kia Rio -90a alternator
DDX470HD GTO14001 GTO1014D (x3)
Big3 in 1/0G
1/0G to GTO14001

sealed boxes have a q factor...but no tuning

i still don't know what you are talking about

I must have gotten some misinformation on the web then about the differences. Q factor is the magnitude that the box amplifies or cuts the frequencies, correct? Then I suppose what I was trying to get at is, would it be ok to have the sealed chamber boosting a different range of frequencies than the vented chamber is tuned to?

If it is fine then answer this question. Typically what frequency does high bass start to drop off and low mid range start to pick up, or the ideal crossover frequency between those ranges. The box I designed, when I finally got the cone excursion within acceptable range the maximum spl is 135 at 95Hz. This box design, at least on paper, dominates over all others with this particular sub on the spl chart, the cone excursion chart, the transfer function magnitude chart, but it of course has some group delay.

Also how do I reduce the air velocity in the ports, its 20m/s.

reduce air velocity? try longer ports. Of course, this changes your tuning as well..

what about those other questions i had?

First, reducing air velocity is all about having larger port opening space.  Use the program to work with some different port opening sizes while keeping tuning freq where you want it to be.  Also, be sure that you are looking at air velocity within the range of audio frequencies that you will likely be listening to in real life (for example, a high velocity at 20 Hz means nothing...where does it hit at 35 Hz?)

Design your bandpass box with the wisdom that you will be changing it a few times to get what you are looking for in sound and performance.  Meaning this:  experiment with unfinished boxes and design your project so that you may make size changes without having to start from scratch each time.  An experienced designer may find a perfect combination of a particular driver and a particular placement in a particular vehicle....but then find that it doesn't work out quite as well in a different vehicle.  Time and patience are your allies when dealing with bandpass, else you end up with something that sounds no better than a prefab that you can pick up at a store.

If your sealed design is "boosting" a range of frequencies, this is a high Q.  You will see that the rolloff is steep as well.  If there is no peak and the rolloff is gradual, you will note that the Q is likewise lower.  Car audio sealed tends toward high Q for a couple of reasons:  limited space for large enclosures, and the desire for booming bass in today's music climate.  Your bandpass needs a marriage of the sealed side with the vented side to produce the sound you are looking for, so prepare for some experimenting.  In other words, with bandpass there quickly must come a time for hands-on building and forget worrying about  logic and assumptions.

And note also, if you want maximum SPL you will want your target to peak in the 50 to 60 Hz range, not 95 Hz.  Your vehicle resonance plays a huge role in this.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Nice... thats really helpful, I'll try and go back and change some things around. What frequency would you consider the end of the line for bass?

Bass goes to midrange at about 400 Hz, but the majority of bass is handled by your front mid drivers.  Sub bass goes up to 80 Hz, maybe up to 100 Hz.  You are dealing with only sub bass with your enclosure.  Try low pass at 80 Hz for your sub, high pass at 80 Hz for the front components.  At that crossover point, sub bass starts dropping off steeply just above 60 Hz, maybe a little higher.  Use  the filters tool in your design software to generate a low pass crossover, 4th order (match the crossover alignment that your amp has).  Click it on and off and watch how the high end of the sub bass drops off.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

holdinmyown wrote:

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man... read my posts. the rear chamber is 64hz, and the front chamber with the port is 80hz, together the box as a whole will generate some mean notes as long as theres not something I don't know about yet... plus I've built plenty of plain sealed and vented and I want to step it up. So if anyone has built these in the past and has some good tips I'd like to know them. 

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dude your post states 16Hz. & you wanna "step it up" from ported boxes? Here is a quick lesson as to why BP boxes came into being. Size. back in the day, a 12" sub would require about 7 cubic feet of air space for a ported box, & would not perform well sealed with low freq. unless a large box was used, but then power handling was sacrificed. Also, with a BP box, the only sound you hear is the port tuning, you do not hear the distortion coming from the sub, & because of this cheap sub makers started using them to make their cheapy subs sound better....the down side, is you do not hear the sub crying for mercey. 

Now, those BP boxes could be made smaller by sacrificing a smooth responce, for being efficient at 1 freq. or 1 group of freq...& depending on the box, a freq. & it's octave. i.e 40Hz & 80Hz., but there is a lul in the output between those freqs., & the rolloff is quite steep, so 30Hz is prob. 7-10db down from the peak freq. in our 40Hz example

Those that posted above are correct, 80Hz (or around there) is a proper x-over point for a sub, never in a car audio subwoofer application should freqs. above 120hz ever be used. all it does is muddy the sound, make the bass directional, & lowers power handling of the sub.

Here is some solid advice. Post up here what kind of car you have, & maxximum box dimentions you can have, & see what some of us come up with for ya. I would almost bet for output most will make a big slot ported box, & if you want accuracy, most would make a moderate sized sealed.

So, post car, year make model, Amplifier model #, & rated output

Size & model # of sub, as well as how many you are using

& size restrictions

A little more advice, be nice to those you are asking for help, & they will give better answers. Now give an apple to the teacher.....sucka LOL

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used to be loud, used to be fast...now I am married LOL