4th order bandpass enclosure (fi Q 12")

[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 given sub perform better in a 4th bandpass or a normal ported enclosure with an ebp of 87 and a qts of .371?

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!

[Swordlordboy1234]

I'd go between 1.5 : 1 and 2.5 : 1. Id lean more to 1.5-1.75 to 1 ratio. Build 1 side to the sealed Reccomended. Then take that to find the 1.75 part of the ratio. Tune between 44and 48hz. That should still dig down to 25hz. Most people tuning to 42 reach down to 20 and that's much much lower.

Most people with 4ths say to give 16-22 sq inches of port per cube with a slot. (Normal ported being 12-14 sq inches) so if I guess with aero ports (normal ported being 8-12 sq inches of port per cube) so my guess would be to shoot for 14-16sq inches of port per cube with an aero.

Definitely invert the sub.

Power handling depends on the ratio you choose, closer to 1:1 you will lose power handling, lose SPL and gain bandwidth. Closer to 3:1 you will gain power handling (mechanically), spl, and lose bandwidth.

The high qts option and stuff I don't think is needed, I'm sure it could help. I've heard that higher qts subs can handle playing lower below tuning.

If you have an android phone then download the ultimate car audio App from xplicit.

Those are all the questions I could answer off the top of my head. Hope it helps.

[Miguels]

I'd go between 1.5 : 1 and 2.5 : 1. Id lean more to 1.5-1.75 to 1 ratio. Build 1 side to the sealed Reccomended. Then take that to find the 1.75 part of the ratio. Tune between 44and 48hz. That should still dig down to 25hz. Most people tuning to 42 reach down to 20 and that's much much lower.

Most people with 4ths say to give 16-22 sq inches of port per cube with a slot. (Normal ported being 12-14 sq inches) so if I guess with aero ports (normal ported being 8-12 sq inches of port per cube) so my guess would be to shoot for 14-16sq inches of port per cube with an aero.

Definitely invert the sub.

Power handling depends on the ratio you choose, closer to 1:1 you will lose power handling, lose SPL and gain bandwidth. Closer to 3:1 you will gain power handling (mechanically), spl, and lose bandwidth.

The high qts option and stuff I don't think is needed, I'm sure it could help. I've heard that higher qts subs can handle playing lower below tuning.

If you have an android phone then download the ultimate car audio App from xplicit.

Those are all the questions I could answer off the top of my head. Hope it helps.

i thought bandpass box got the lows from the sealed side not by the ported section and the reason it is tuned lower is when they are built at 3:1 ratio or when they get peaky

[lyons238]

I'd go between 1.5 : 1 and 2.5 : 1. Id lean more to 1.5-1.75 to 1 ratio. Build 1 side to the sealed Reccomended. Then take that to find the 1.75 part of the ratio. Tune between 44and 48hz. That should still dig down to 25hz. Most people tuning to 42 reach down to 20 and that's much much lower.

Most people with 4ths say to give 16-22 sq inches of port per cube with a slot. (Normal ported being 12-14 sq inches) so if I guess with aero ports (normal ported being 8-12 sq inches of port per cube) so my guess would be to shoot for 14-16sq inches of port per cube with an aero.

Definitely invert the sub.

Power handling depends on the ratio you choose, closer to 1:1 you will lose power handling, lose SPL and gain bandwidth. Closer to 3:1 you will gain power handling (mechanically), spl, and lose bandwidth.

The high qts option and stuff I don't think is needed, I'm sure it could help. I've heard that higher qts subs can handle playing lower below tuning.

If you have an android phone then download the ultimate car audio App from xplicit.

Those are all the questions I could answer off the top of my head. Hope it helps.

i thought bandpass box got the lows from the sealed side not by the ported section and the reason it is tuned lower is when they are built at 3:1 ratio or when they get peaky

i was going to say the same thing.

hopefully someone else can chime in. im really trying to decide if a bandpass will help me get louder while still hitting a decent band 28-65hz mainly. will a blow through bandpass setup correctly get me what im looking for or would a normal ported box blocked by the rear seats be better? im just not sure given my sub has an ebp of 87 and a qts of .371. thanks!

[Miguels]

you will have to build both to know which is better. in theory the bandpass without anything blocking the port has the potential

[lyons238]

you will have to build both to know which is better. in theory the bandpass without anything blocking the port has the potential

Any comment on the ebp/qts specs of my sub for a bandpass enclosure? It seems the sub is more geared towards a 6th order or ported enclosure but I feel like a 6th order would be a bit over my head.. but people tell me this sub works well in a 4th too even without the high qts.

Any other comments to my other questions?

[philrab]

you will have to build both to know which is better. in theory the bandpass without anything blocking the port has the potential

Any comment on the ebp/qts specs of my sub for a bandpass enclosure? It seems the sub is more geared towards a 6th order or ported enclosure but I feel like a 6th order would be a bit over my head.. but people tell me this sub works well in a 4th too even without the high qts.

Any other comments to my other questions?

I was in the same boat deciding between a 4th or 6th for my SA12. Already in a ported box, so I have a benchmark to hopefully exceed for output and bandwidth. What made my decision was modeling the current ported box in WinISD (SA12, rated power, 2.15 cubes tuned to 33 hz) and overlaying a possible 4th and 6th order based on the same sub and power over it. Between a 4th and 6th, the SA really seamed to work better in a 6th, so that's the route I'm taking. They've been done in 4ths, and they work, but WinISD let me play with the designs and compare directly.

[lyons238]

you will have to build both to know which is better. in theory the bandpass without anything blocking the port has the potential

Any comment on the ebp/qts specs of my sub for a bandpass enclosure? It seems the sub is more geared towards a 6th order or ported enclosure but I feel like a 6th order would be a bit over my head.. but people tell me this sub works well in a 4th too even without the high qts.

Any other comments to my other questions?

I was in the same boat deciding between a 4th or 6th for my SA12. Already in a ported box, so I have a benchmark to hopefully exceed for output and bandwidth. What made my decision was modeling the current ported box in WinISD (SA12, rated power, 2.15 cubes tuned to 33 hz) and overlaying a possible 4th and 6th order based on the same sub and power over it. Between a 4th and 6th, the SA really seamed to work better in a 6th, so that's the route I'm taking. They've been done in 4ths, and they work, but WinISD let me play with the designs and compare directly.

I'll have to play around with it in not the best using winsd and I don't see a lot of options such as like port velocity and stuff like that, maybe I just sont know how to use the program.

Also, keep in mind I will be using a 2000w amp on he do q which is rated at 1500w. So after losses I will probably feeding the sub around 1700-1800w rms. Wouldn't this type of power be best in a 4th order? I'm worried I'll blow the sub with that kind of power in a 6h order.

[Triticum Agricolam]

I'll have to play around with it in not the best using winsd and I don't see a lot of options such as like port velocity and stuff like that, maybe I just sont know how to use the program.

Also, keep in mind I will be using a 2000w amp on he do q which is rated at 1500w. So after losses I will probably feeding the sub around 1700-1800w rms. Wouldn't this type of power be best in a 4th order? I'm worried I'll blow the sub with that kind of power in a 6h order.

I doubt your sub sees even 1500 watts, I wouldn't worry about power handling.

Port velocity and other specs are all there in WinISD, you just have to look around for them.

What makes you think your sub won't handle a 6th order BP but will handle a 4th order BP?

[Raptorman]

I'd go between 1.5 : 1 and 2.5 : 1. Id lean more to 1.5-1.75 to 1 ratio. Build 1 side to the sealed Reccomended. Then take that to find the 1.75 part of the ratio. Tune between 44and 48hz. That should still dig down to 25hz. Most people tuning to 42 reach down to 20 and that's much much lower.

Most people with 4ths say to give 16-22 sq inches of port per cube with a slot. (Normal ported being 12-14 sq inches) so if I guess with aero ports (normal ported being 8-12 sq inches of port per cube) so my guess would be to shoot for 14-16sq inches of port per cube with an aero.

Definitely invert the sub.

Power handling depends on the ratio you choose, closer to 1:1 you will lose power handling, lose SPL and gain bandwidth. Closer to 3:1 you will gain power handling (mechanically), spl, and lose bandwidth.

The high qts option and stuff I don't think is needed, I'm sure it could help. I've heard that higher qts subs can handle playing lower below tuning.

If you have an android phone then download the ultimate car audio App from xplicit.

Those are all the questions I could answer off the top of my head. Hope it helps.

Anything below 2:1 is a waste imo. Tuning point is the resonant frequency of your sealed chamber, not just a guess.

Port area is strictly based on your cone area/volumetric displacement, not tied into your ported chamber volume whatsoever.

Yes invert the sub.

Power handling is based on sealed volume/port area. Bandwidth will hardly diminish whatsoever from higher ratios, to a certain extent. 3.5:1 is the most I'd do for musical.

High qts option is Fi's way of saying "Sealed box friendly", which, also means 4th order friendly. So get high qts if you can.