ok, going to build a box for my ID8s. going to angle the back to sit flush to my back seat to help save space instead of making a plain square/rectangle shape. problem comes with the port. I attached a real crude drawing I did in paint, the small diagrams are how I think you are supposed to measure port length when the back wall of the box is plumb just like the front of the box. the large one is the way I am guessing you would measure port length when they arent, if its even doable. red is interior port wall blue is point at which I figure Id measure port length.

 

so, whats the verdict?

Square it off in the back.  You have to have even walls to really know what is happening.  It will be easier to build squared off and the part behind the port will still be part of the box volume so the gains of the slant still exist.

I'd go with the trusted and true rectangle shape ported and tuned. Enclosure shouldn't be that large for a pair of ID8s.

Just saying.

an aeroport would be the easiest solution. 

41 minutes ago, Randal Johnson said:

Enclosure shouldn't be that large for a pair of ID8s.

Lord, I didn't read 8's.  No way, no how does that enclosure work.  WAY too big.  Ported 8's in general are a meh idea as the box ends up being nearly as large as if you used a much larger driver.

you guys did read the part I wrote about it being a "crude drawing" and the fact that no dimensions were called out. lol. only question was about port measurements, not enclosure size. its going to be 1.3 ft^3 net @ 33hz port is 1x13.5 ~21 long. max velocity 82 ft/sec port resonance 313hz. would like the port to be a little bigger but Ive read up to 110 ft/sec is acceptable and the first port size I chose keeping it down around 60 was 32" long

 

but thanks, Ill make the port square and not follow the rear wall. should I put the port as far back as I can or should I bring it forward a little bit so the airspace behind the port isnt so tight? if I go right to the back wall the cross section of the dead space behind it will be 13.5H x 0"W1 / 5"W2. havent got the exact dimensions yet but the port will go about 17" across the back of a ~26" inside dimension box.

 

if I kill that dead spot all the way across the box it will only lose .5 ft^3. I would have to only bring the box about 2.5" out but that is almost half the depth of the box at the top so its a decent loss considering I only have 8s to save space so that 2.5" does matter somewhat.

heres a better likeness of what Im imagining, once I have the port placement figured out I can start accouting for port/sub displacement in my final calculations.

 

thanks

 

oh, also, I have the 8s from the truck I traded in, I have the amp from another build, figured why not use them and keep as much of my hatch free for hauling crap as possible for now. wouldnt buy 8s for the car as a first choice. eventually looking at a single 12 like a lethal injection, GCON, ICON, something along that price range, or a pair of less expensive 12s like RE SCX, IA I12, etc... enclosed/powered accordingly. but Im going to get these 8s in and do a good front stage first this time. best Ive ever had were some audiobahn components off of about 60 watts, made me happy at the time, then always had cheap coaxs, until I just had a bmw with the logic 7 system for a while and man that sounded pretty good, so I would like something like that this time around.

You might try to keep things simple and go with a 4" PVC round port. 

4" round will have port velocity closing in on 100 ft/sec and still be 17.5" long, I'm guessing you measure the same way with a pvc elbow in the port construction, you measure the port down the middle and pull from where the lines intersect in the elbow?

I think that's the way Ray and Mike designed my enclosure. Can't remember. Maybe a better enclosure deaigner will chime in on this.

100'/sec no thanks.

The port can run from front bottom to the back and up the back wall , if box height permits, maintaining a true shape and length.

3 hours ago, ///M5 said:

100'/sec no thanks.

 

whats an acceptable amount. I can keep it down to about 72 ft/sec or if the port went to the back wall, up to the top, turned again and came back towards the front I can get it down to about 60 ft/sec

Depends on where it is and your tolerance.  In normal listening I surely don't want mine above 20', but you and I are probably different cats.

its in a 94 integra, in the hatch area. port/sub both facing rearwards. only thing separating cargo area from cabin is a thin carpeted shelf probably made of some kind of pressboard like the 1/8" stuff lining the bottom of most trunks over the spare.

 

I will play around with lowering the velocity. or I will just say screw the 8s and use my REX12 and build a ported box for that in there. might as well build it a size that will work good for whatever 12 I want to upgrade to as long as its anywhere close to suitable for the RE.

 

how do you get it so low? I might be using winisd wrong or something, just stared using winisdpro alpha, might have to go back to regular winisd beta... I input 900 watts under the signal tab, and for 2ft^3 tuned to 35 I need a port of 14"x8" 114" long to keep port velocity down to around 20...

 

Yup, sounds about right. The software is accurate enough and you're likely using it correctly, finding a middle road capable of delivering you what you need with compromise in the right places is the key that experience will eventually get you. 

In a trunk port noise is harder to detect, so you can scrape by with less port area a bit easier if that's the case.  Small enclosures are always harder to deal with when it comes to port design because of how much faster exponentially the port length grows as tuning is lowered or port area is increased.  You may have to model and build a few different designs to learn for yourself and decide which compromises you can and can't live with.

 

Alton is correct on this. In my experiences enlarging the port opening will reduce velocity. That being said, with doing so also will lengthen the port to maintain proper tuning. Larger ports will also devour displacements inside the enclosure quickly. That's why people who are very restricted with space will choose aero ports or schedule 40 pvc pipe.

Everything is a compromise in car audio.  Yay!

ok, I got my box designed and ready to go, just have one more question I dont think Ive ever gotten the answer to before (no matter which way it goes though I will probably just build it as is) is how you measure port length if it ends the same as the port width from the back wall. I dont know if I measure to the end of the port. or exit the port halfway to the box wall, turn and go to the edge of the port wall. included is another fancy paint drawing to show what I mean. if its the way I think it is, its 1.412 @ 35.8 or if not its [email protected].

 

hope I can get some work in on the box tomorrow but probably not.