Ported box, do I have the specs close enough?

[skervyskalywag]

Total noob to box building never done one in my life. Saw some boxes from posts and websites but none really fit my space needs. I downloaded winisd watched some videos read a ton of posts and went to work. This is what I came up with, plan is to make 2 of them, 4x 12 c2 audio threatcons on around 2k right now possible upgrade to 3k if I can convince myself to buy 2nd battery which I dont want to. I wanted the option of only running 2 subs or being able to easily remove if need, so no massive single box. The only variation is that the subbox site has the port length a couple inches shorter. It will be 29in since thats what all of the calculators and winisd come up with. i have around 42-44in width, 33-34 depth, 15-16 height to work with. 

Am I in the right ballpark with this? And Im a little confused on port velocity. Ive seen some stuff saying it needs to be under 17, others saying it needs to be under 30 or mid 20. Seems like a pretty big range

 

 

[Joe X]

You need to be below 30 m/s to avoid the worst from low port area, and you target a lower airspeed according to your needs, the ultimate way of checking how your port is doing is looking at your impedance curves (advanced topic), you may want to take a look at the following thread for some more infos on ports because raw port area is not the only thing that goes into an efficient port:

 

 

[skervyskalywag]

49 minutes ago, Joe X said:

This forum is so weird I dont know if its my browser or just how this site works lol. Cant type anywhere when I try to reply except your quoted window and even if I refresh the page it just loads it right back up where I left off trying to delete yours. Anyways I already read that along with a bunch of other forums on the topic. I just need to know if the box I came up with looks close enough or something dramatically wrong. Not worried about fine tuning optimal yada yada right now. Just making some starter boxes so I can get rid of this junk prefab. I ran em sealed in my car before but now itll be in a suv and sealed aint gonna be hard enough or fit well facing the back how I prefer the sound

[Joe X]

You have chosen a spec as follows on a per driver basis:

 

2 cubic feet net 32 Hz and 27 square inches of port area (per driver).

 

1) Port area will be good for the threatcon-2 (600w) drivers but not for the threatcon-4 variant which were 1200W or 1500W RMS.

 

2) your port is too thin making the port inefficient, best is to keep 6:1 heigh to width ratio or lower.

 

3) SUV boxes are subs up /port back.

 

4) generally 2 12s are lackluster in a SUV, probably that's what you will find out.

 

That's about it.

 

 

 

 

[skervyskalywag]

Already aware of all those points except

 

6:1 port ratio? First time Im seeing that anywhere. Everyone talks about the air velocity and chuffing whatever which I already mentioned the ranges I read and still confused on that. What exactly about the port I have makes it inefficient?

 

I already have 2 hooked up in a crappy old prefab box my brother had laying around. Id prefer all 4 and the boxes are designed for sub up/port back. I just need to option of easily removing 2 or all for space when needed. 

 

[Joe X]

The area ratio issue is explained in the first post of the thread I told you about, bottom line is friction losses, you want to minimize the amount of contact surface for a given port area, in order of efficiency circular is best, 5 or more sided regular polygons, the square port and then the rectangular ports which get worse as the area ratio increases. This is one case in which you may want to increase port area as a countermeasure if you have to go with a high area ratio port.

 

 

BTW further information regarding port area ratio and other slot port design guidelines can be found at JL Audio's support articles at jlaudio.com.

 

[skervyskalywag]

I have read that post before and just read it again now, it states nothing about what your saying of a 6:1 ratio or what basis youre using to say its inefficient. That post is about surface area. I adjusted the dimensions slightly and increased the port to 3in. Cant do any larger or it wont fit. Air velocity peaks at 20 now. Im not trying to fine tune or do aeroports or hexagons or any of that. I just wanted to know if Im in the right ballpark area. ill add some flares to the outside of the port and round the corners and paint the inside for a smooth finish whatever etc. Just want someone to confirm if the specs are in the right ballpark for a 32hzish port lol. And also a little on the confusion between people saying 17 peak air velocity vs others saying 30 or mid 20s

[Joshdashef]

12 hours ago, skervyskalywag said:

I have read that post before and just read it again now, it states nothing about what your saying of a 6:1 ratio or what basis youre using to say its inefficient. That post is about surface area. I adjusted the dimensions slightly and increased the port to 3in. Cant do any larger or it wont fit. Air velocity peaks at 20 now. Im not trying to fine tune or do aeroports or hexagons or any of that. I just wanted to know if Im in the right ballpark area. ill add some flares to the outside of the port and round the corners and paint the inside for a smooth finish whatever etc. Just want someone to confirm if the specs are in the right ballpark for a 32hzish port lol. And also a little on the confusion between people saying 17 peak air velocity vs others saying 30 or mid 20s

 

For car audio purposes port velocity is not as important as say audiophile levels of 17 peak air velocity. Most shoot for the 30 meters per second mark because fitting a port that only has 22 meters per second is very hard. You improve peak output and reduce chuffing with properly sized ports with lower air velocity. I would shoot for 30 meters per second or under at a minimum, but 25 is perfectly acceptable - especially if you introduce round overs or a kerf port, but at that point why not increase port size? You can input RMS power into winisd too under signal > system input power. 

 

The order for efficiency is as follows (Highest to lowest efficiency); Circle, Octagon, Hexagon, Square, Long Rectangular/Slot. The further you stray from a perfectly circular port the less efficient it is essentially. That is why rectangular ports have such a huge drop off on surface area than slots, but slots are great because they offer rigidity and are space efficient because your using an exterior wall for a side of the port.

 

Below shows the breakdown for your specific port with 54.6 inches squared port area, 29.67 long, slot port 19.5 x 2.8 (19.5/2.8=6.96 Port Ratio) 

also; *[19.5/3=6.5 Port Ratio]* 

 

As you can see the volume of a slot port is almost the same as an aero port but the walls of a rectangle are longer (higher surface area) than that of a circle port. 80% circular port is for those who like to use aero efficiency to make port smaller, but I would not recommend it. 

[Joe X]

17 hours ago, skervyskalywag said:

I have read that post before and just read it again now, it states nothing about what your saying of a 6:1 ratio or what basis youre using to say its inefficient. That post is about surface area. I adjusted the dimensions slightly and increased the port to 3in. Cant do any larger or it wont fit. Air velocity peaks at 20 now. Im not trying to fine tune or do aeroports or hexagons or any of that. I just wanted to know if Im in the right ballpark area. ill add some flares to the outside of the port and round the corners and paint the inside for a smooth finish whatever etc. Just want someone to confirm if the specs are in the right ballpark for a 32hzish port lol. And also a little on the confusion between people saying 17 peak air velocity vs others saying 30 or mid 20s

 

I tried to enter the box dimensions you provide above and I get  3.65 cubic feet tuned to 34.4Hz so you might have missed to enter driver displacements.

[skervyskalywag]

9 hours ago, Joe X said:

 

I tried to enter the box dimensions you provide above and I get  3.65 cubic feet tuned to 34.4Hz so you might have missed to enter driver displacements.

 

Did I miss something? That first one should have still been 4cf with a total volume of 5cf something including displacement and port. This is what I came up with for the finalized version. Im still playing with the width some. Sub displacement numbers were just some I googled so I didnt have to do the math lol. I was under the impression its adding the sub displacement because when I add the .12 in there it brings up the total volume and depth. Also the port length will be about 30/31 depending what I settle on for the box width. The subbox site shows a little shorter than winisd. Im not hugely concerned with being exactly on the dot for turning id prolly be fine anywhere 30-35 for my needs but lower the better

https://subbox.pro/en/design/?bt=2&bw=859.8&bh=533.4&bv=113.3&mt=19&fp=1&sq=2&ss=12&cd=285&md=160&sv=3.4&so=101.6&sd=0&sb=&sn=&pt=3&pq=1&rf=32&pd=218.34&pw=2&pa=374.22&pp=0