Help with 4th order bandpass (12" fi Q)

[lyons238]

I have a 12" fi Q that is fully loaded, except there is no extra spider option, and no high qts option. I also have a Sundown SCV-2000d, big 3, XS Power d3400, and an XS Power XP950 in the trunk for power. I figure after all losses/drops I should be getting around 1700w rms of clean power to the sub. For mide I have 2x 6.5" Sundown Neo Pro V2's and some Image Dynamics CTX65SC's for components up front. Hopefully having some dedicated mid bass drivers will work well with a bandpass enclosure, so that I can tune that to hit the low notes and roll off right into where the Neo Pro's will take over. Lastly, It is being installed in a 2013 Subaru WRX.

After some deliberation I think I have landed on a 4th order bandpass enclosure that is vented into the car cabin through the rear deck to maximize SPL, while retaining some good SQ in my car. However I have some questions before I move forward.

1. Will a 4th order bandpass enclosure that is vented through through the rear deck provide more SPL than a simple ported enclosure with the rear seats blocking? Does a 4th order bandpass enclosure provide more SPL without factoring in the loss from the rear seats? Also, will my sub with a ebp of 87 and a qts of .371 perform better in a 4th order over a normal ported enclosure?

2. What ratio should I use for this sub? I was thinking 2:1. 1.15 net cuft sealed : 2.3 net cuft ported. This is within the manufacturers recommended sealed/ported volume. With a bandpass box, are the manufacturer's recommended volume specs the way to go?

3. What should I tune it to? Also, what is the roll off amount per octave with a 4th order bandpass? Does volume, port area, etc affect this? I would like for this setup to be somewhat SQ oriented but to also maximize SPL with my given gear. I like to get low 25-30hz but also want it to be able to hit the higher notes.

4. Will a 6" aero port be effective in this application,? How much port area per cuft is recommended for a bandpass enclosure, is it the normal 12-16 sqin/cuft or is it more like 14-20 sq in/cuft? I believe a 6" aeroport has 28.26 sqin of port area, which is only about 12.3 sqin per cuft, is that enough considering its an aero port and not a slot? Or should I try and make or find a 8" aeroport? Am I calculating that correctly? Is length not considered when determining port area?

5. How do I calculate the port displacement to get the proper net volume of the ported chamber? In order to vent through the rear deck the aero port will stick out of the box. In order to calculate tuning and net volume, how would I figure out the volume of just the port that is inside the box, including the flare? Also, wouldn't that be contradicting because in order to figure out port length and tuning I need to know the amount of volume for that chamber, but I won't know that until I figure out the port area that is inside the box?

6. Will the non qts fi Q be best fit for this enclosure or is the qts option better?

7. Should I mount the sub with the basket in the ported chamber to reduce heat/coil issues? Also, would I need to reverse the wiring when mounting like this or is that only needed when your running multiple subs mounted opposite ways in the same sealed enclosure?

8. Will 1700w rms be too much? Does a 4th order bandpass reduce power handling or will it be similar to a ported enclosure?

9. Which is better for a 4th order bandpass the high qts option for the fi Q or no high qts option. My sub is the no high qts version which has a qts of .37 because I was originally planning on going ported. Will this be okay for a 4th order? What is the qts of a high qts fi q?

Any help is greatly appreciated as I want to make sure that I get this enclosure perfect for my application. Thanks!

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[lyons238]

any help? i know its a lot but i want to make sure i cover every concern before building.

 

[plexlove]

Odds r u wont get any help from people in here...most of em are *****. Ive tried several times.

As far as ur questions...theres a thread on 4ths on here, search and find it...gotta lot of reading to do! Lol

Most of ur questions are very simple ones and if some of the aholes in here read them i can tell u right now they would just tell you if u dont know this stuff u shouldnt be building it!

They dont like to teach people!

But for real, not to be a **** but u really do need to research! No sense in trying to build a very complicated enclosure if u dont know ur stuff. Everything u asked is posted....good luck

 

[lyons238]

Odds r u wont get any help from people in here...most of em are *****. Ive tried several times.As far as ur questions...theres a thread on 4ths on here, search and find it...gotta lot of reading to do! Lol

Most of ur questions are very simple ones and if some of the aholes in here read them i can tell u right now they would just tell you if u dont know this stuff u shouldnt be building it!

They dont like to teach people!

But for real, not to be a **** but u really do need to research! No sense in trying to build a very complicated enclosure if u dont know ur stuff. Everything u asked is posted....good luck

It's my first bandpass box I already know many of these questions thank you! I need to do some modeling.

 

[plexlove]

Yeah im in the process of building a 4th for my 2 zv4 sundown 18s and asked for a lil help and got nothing lol.

Researched non stop for 2 days and off and on this whole week and still cant find the answrr im needing.

Basically as long as the sub u have will work well in one its kinda up to u dependig on what ur going for for the rest.

Im doin 3to1 ratio, subs firing into the sealed to help with cooling and so i can smell if somethings wrong. Doin 2.75 each sub sealed and 18ish ported, 15.5 after all displacements.

245 inches port area tuned to 42hz. Tune higher than normal because of the sealed box! Most tune to 45hz but i wanna make sure i get the lows.

Runnin 1/4" steel bar in 4 strips on the bottom of my bed in my avalanche and bolting them down, then runnin 4 more on top of my box and runnin .5inch allthread from top to bottom for bracing. Cant think off any better way to brace than that and should help drastically with box rise!

Glassing the inside and doin 45s on all corners...only 2 things i havnt figured out is if to use a square port or aero and also i have an fc of like 67hz....that thew me!

I tried asking what i should tune to since my fc is so high in my sealed box but get absolutely no help. Just a bunch of smartasses talking crap for no reason!

Guess ill just wing it...its only 1400 dollars if they go up in smoke lol.

If u have any questions that u cant figure out after researching, pm me ill be glad to help if i can! Good luck man

 

[GroundPounderFI]

4th orders are easy to do, all you gotta do is build a sealed section, then a ported section. lets say you build a sealed section that's about 1.5 cubes for your 12, build another section that's a little bigger like 2 cubes for the ported section, then from there its basically like a ported box. tune it to what you want to, if you tune low its not gna make your low end sound any better cuz that's what the sealed section is for. it will just sound like **** on the high notes. tune a little high so you can hit those high notes, a lot of guys think that tuning low on the ported section will make it even better, u can but the high bass wont sound good. ppl do 4th orders to get the best of both world, painful high notes to hurricane lows. best thing to do is do plenty of research and you will be able to build it yourself and make it sound the way you want

 

[lyons238]

Yeah im in the process of building a 4th for my 2 zv4 sundown 18s and asked for a lil help and got nothing lol.Researched non stop for 2 days and off and on this whole week and still cant find the answrr im needing.

Basically as long as the sub u have will work well in one its kinda up to u dependig on what ur going for for the rest.

Im doin 3to1 ratio, subs firing into the sealed to help with cooling and so i can smell if somethings wrong. Doin 2.75 each sub sealed and 18ish ported, 15.5 after all displacements.

245 inches port area tuned to 42hz. Tune higher than normal because of the sealed box! Most tune to 45hz but i wanna make sure i get the lows.

Runnin 1/4" steel bar in 4 strips on the bottom of my bed in my avalanche and bolting them down, then runnin 4 more on top of my box and runnin .5inch allthread from top to bottom for bracing. Cant think off any better way to brace than that and should help drastically with box rise!

Glassing the inside and doin 45s on all corners...only 2 things i havnt figured out is if to use a square port or aero and also i have an fc of like 67hz....that thew me!

I tried asking what i should tune to since my fc is so high in my sealed box but get absolutely no help. Just a bunch of smartasses talking crap for no reason!

Guess ill just wing it...its only 1400 dollars if they go up in smoke lol.

If u have any questions that u cant figure out after researching, pm me ill be glad to help if i can! Good luck man

sounds good man, only thing is i would look more into that fc and the tuning before you wing it. otherwise sounds like you have a good plan!

4th orders are easy to do, all you gotta do is build a sealed section, then a ported section. lets say you build a sealed section that's about 1.5 cubes for your 12, build another section that's a little bigger like 2 cubes for the ported section, then from there its basically like a ported box. tune it to what you want to, if you tune low its not gna make your low end sound any better cuz that's what the sealed section is for. it will just sound like **** on the high notes. tune a little high so you can hit those high notes, a lot of guys think that tuning low on the ported section will make it even better, u can but the high bass wont sound good. ppl do 4th orders to get the best of both world, painful high notes to hurricane lows. best thing to do is do plenty of research and you will be able to build it yourself and make it sound the way you want

ok thanks for clearing that up. how do you recommend tuning the ported section? am i supposed to match and tune to the fc of the sealed section? also is there an equation to figure out the fc of the sealed? i believe i had it written down somewhere but i forgot or lost it. also, do you think a 2.5:1 ratio would be a good balance of output/bandwidth?

 

[Jeffdachef 5,000+ posts]

Depending on your woofers, you will have a hard or easy time getting a wide range of frequencies. The design itself starts to get peaky after a 1.5 to 1 ratio most of the times but thats how you get the spl from it, theres always tradeoffs, higher ratio, the less bandwidth but spl improves greatly. Id model the woofer in winisd's 4th order graph. 45 hz is not a standard, its just something that makes the sub model well for them. You need to play around with the ratios and compare how they model out to get a good sense of how the sub will sound like.