4th order question

[Jake Pichola]

so i designed a 4th order enclosure for 2 12's. i have 6 cuft in the sealed part and 18 cuft in the ported part. does this sound right? im going for a 3:1 ratio and i was wondering if i have the airspace right for the sealed and ported because i always see pictures of builds with 18s and 15s where the sealed part looks so small.

[Jake Pichola]

so i designed a 4th order enclosure for 2 12's. i have 6 cuft in the sealed part and 18 cuft in the ported part. does this sound right? im going for a 3:1 ratio and i was wondering if i have the airspace right for the sealed and ported because i always see pictures of builds with 18s and 15s where the sealed part looks so small.

so its 3 cu per sub sealed and 9 cu per sub ported

[RooTxBeeR]

Are you asking if you followed a 3:1 ratio right or if a 3:1 ratio is good? Hard to understand what you want out of this.

[Jake Pichola]

Are you asking if you followed a 3:1 ratio right or if a 3:1 ratio is good? Hard to understand what you want out of this.

if the airspace is good for 2 12s. i just want to make sure im not building this too big for 2 12 inch subs,

[Kyblack76]

Im going to half less that 6cubes in the sealed section for 4 15's ........

[RooTxBeeR]

Yeah 3 cuft per 12 sealed might be big. I usually see them in 1.5-2.5. I am a noob though.

[Jake Pichola]

how about 2 cu sealed and 6 cu ported, is that a good size for spl?

[Triticum Agricolam]

What subs are you using, how much power are you going to run, what are you tuning the front chamber to? What are your goals for this system, what kind of bandwidth are you hoping to get out of the box? What vehicle is this going in? There are no generic designs for bandpass boxes. They need to be designed for the specific application they are going to be used for.

Forget everything you have ever read about bandpass box ratios, they are a design shortcut for people that don't understand bandpass boxes and often times do more harm than good. This is exactly what is happening to you. 18 cu ft is a ridiculously large front chamber size for two 12"s. Correct me if I'm wrong, but it kinda sounds like you just picked a number out of the air for your rear chamber volume and then multiplied it by three to get your front chamber volume. That's kinda like walking into a shoe store without knowing what size shoe you wear and just picking a number, buying a shoe that size, and hoping it fits well.

[Jake Pichola]

What subs are you using, how much power are you going to run, what are you tuning the front chamber to? What are your goals for this system, what kind of bandwidth are you hoping to get out of the box? What vehicle is this going in? There are no generic designs for bandpass boxes. They need to be designed for the specific application they are going to be used for.

Forget everything you have ever read about bandpass box ratios, they are a design shortcut for people that don't understand bandpass boxes and often times do more harm than good. This is exactly what is happening to you. 18 cu ft is a ridiculously large front chamber size for two 12"s. Correct me if I'm wrong, but it kinda sounds like you just picked a number out of the air for your rear chamber volume and then multiplied it by three to get your front chamber volume. That's kinda like walking into a shoe store without knowing what size shoe you wear and just picking a number, buying a shoe that size, and hoping it fits well.

i misread the enclosure recommendations and accidently read the ones for the 15" in ported. but im going to be running 2 soundqubed hd200 12's on 1200 watts. i was looking into maybe 2 cu ft sealed and 6 ft ported. the port will be tuned to 35 hz, and i want more of an spl setup than a high range of frequencies. but thanks alot for pointing all of this out for me because it definetly makes the process faster when someone with experience can help.

[Triticum Agricolam]

No prob.

A 2 cube rear chamber, and 6 cube front chamber is a lot more reasonable numbers for those subs. For a rear chamber I would recommend increasing it a bit to 4 cubes, this will lower the QTC below .7 (which is good) and bring the sealed resonant frequency down below 50 Hz (also good). It will help you get better low frequency output.

35 Hz is way too low of a tuning for the front chamber. Most people tune their front chambers to between 40-50 hz, with 45 hz being a good compromise. If you know what frequency your vehicle peaks at you could tune to there (as long as its around 40-50 hz). Keep in mind that with a bandpass box output drops off pretty quickly above and below the tuning frequency. Its a very good idea to make the port removable or otherwise adjustable so you can tweak the tuning frequency after you play test the box.

For front chamber size, it depends on how peaky of output you want. The larger it is, the more output you will get, but only right around the tuning frequency. I think your plan of 6 cubes is a pretty reasonable starting point.