4th order-care to explain?

[bluegmcjimmy]

what are some of the pros and cons... i have an extra sub laying around the hits pretty hard for 200 rms its a rockford fos punch he or hi 8ohm 12, i build it and give it to some random kid that wants some BASSSSSS

[hdorre]

pro - larger passband, can obtain a flatter reponse

con - steeper roll off, eats softies if sealed is too big

[Smoove]

Has magic DB fairy dust if built correctly

[bluegmcjimmy]

how do you calculate a 4th order?

[Joe X]

7 hours ago, bluegmcjimmy said:

what are some of the pros and cons... i have an extra sub laying around the hits pretty hard for 200 rms its a rockford fos punch he or hi 8ohm 12, i build it and give it to some random kid that wants some BASSSSSS

 

4th bandpass boxes need to be designed and built carefully and often will need further mods to get to work as expected, you will usually need solid midbass on your front stage for it to work really nicely, unless you are willing to spend extra time / work just do ported, it does what's expected to do the first time and it's easy to build.

[bluegmcjimmy]

43 minutes ago, Joe X said:

 

4th bandpass boxes need to be designed and built carefully and often will need further mods to get to work as expected, you will usually need solid midbass on your front stage for it to work really nicely, unless you are willing to spend extra time / work just do ported, it does what's expected to do the first time and it's easy to build.

i heard about you actually i read it on here, they said you do nice boxes.

[Triticum Agricolam]

Joe X hit the nail on the head, you would be wise to consider his advice.  

The one big advantage 4th order bandpass boxes have is they push all the output through the port, this can be really handy in certain situations (blow throughs, firewalled trunks, etc).  If you don't need that capability a ported box is going to be better 99% of the time.

If you want to build a bandpass box just to experiment, that's perfectly understandable.  I can give you my 4th order design philosophy if you want, its SIGNIFICANTLY more involved than designing a ported box though. 

 

 

[bluegmcjimmy]

4 hours ago, Triticum Agricolam said:

Joe X hit the nail on the head, you would be wise to consider his advice.  

The one big advantage 4th order bandpass boxes have is they push all the output through the port, this can be really handy in certain situations (blow throughs, firewalled trunks, etc).  If you don't need that capability a ported box is going to be better 99% of the time.

If you want to build a bandpass box just to experiment, that's perfectly understandable.  I can give you my 4th order design philosophy if you want, its SIGNIFICANTLY more involved than designing a ported box though. 

 

 

yes i would like that, i just have a perfect good sub just sitting doing nothing, it is worthy of being used.

[Triticum Agricolam]

4 hours ago, bluegmcjimmy said:

yes i would like that, i just have a perfect good sub just sitting doing nothing, it is worthy of being used.

Here ya go:

First start with the rear chamber. The rear chamber determines what output you are going to get and controls cone excursion below the tuning frequency of the front chamber. The bigger you make the rear chamber, the more low end output you will get and the lower your sealed resonant frequency will be, but as you make it bigger your cone excursion goes up too. It's a balancing act to try to make the rear chamber as big as you can to get the most output, but without having it be so big your subs destroy themselves the first time you play a low note at war volume. The manufactured recommended sealed box size is a decent starting point for rear chamber sizing, but you still need to check and see what you get.

 

The front chamber size determines what output you will get around the tuning frequency.  Bandpass boxes let you trade efficiency for bandwidth and vice-versa.  The bigger you make it the more output you get, however you only get output over a limited frequency range. Make the front chamber too big and you get a one-note-wonder. Just how big you should make it depends on the parameters of your subs.  Some subs will give you wider bandwidth than others will using the same size front chamber. Subs with lower QTS and/or Vas will be more peaky than subs with higher QTS and/or Vas, this will make some subs inappropriate for 4th order bandpass box usage. Just how peaky you want the output to be depends on your personal goals and listening tastes.  Everything is a trade off. 

 

When it comes to the tuning of the front chamber you can move the tuning around a bit to get the frequency response you want, but generally you will get best performance with it being near the sealed chamber resonance, this is another reason why its a good idea to keep an eye on your sealed chamber resonance when sizing your rear chamber. Its a good idea to make your front chamber port adjustable so you can tweak the tuning a bit when you get it in the vehicle. Tuning frequency on paper doesn't always work out to what you get in practice and you may want to shift your passband up or down a bit to fit your listening tastes.

 

In terms of port area for the front chamber, you need to have a lot.  All of the output has to come out of that port, so you don't want to lose output to air resistance due to an undersized port.  At 30+ m/sec you can lose half, or more, of your output to port compression  I try to keep port velocity under 20 m/sec if at all possible, though it may not always be.  Depending on how much power is going to be used, this can require ports as big as 1/2 the cone area.

 

A lot of people try to really over-simplify bandpass box design, this leads to shortcuts like using "ratios" that will often bite you in the ass. In my opinion, acoustic modeling software (WinISD, BassBoxPro, TermPro, HornResp, etc) is a must for bandpass box design. Otherwise you are just taking shots in the dark, you may be know which direction you are shooting towards, but without software you can't see where you are hitting until the box is complete. It takes some experience to use the software well and to know how to interpret the results, but this still a whole lot better than trial and error.  

[dsw422]

Do all sealed chamber sizes reflect the same resonant tuning no matter the sub? Is it unusual to see sealed chamber size larger than the ported side? Can tuning the ported chamber higher than the sealed increase ouput? Thanks for any responses