Porting a small fiberglass box?

[RcRacerDrew 10+ year member]

Well my 200 pound brick of a vented box for my A15s is huge and weighting my car down bigtime. I have come to the realization that I need a box for daily driving, something that takes up less room and that is less weight. Since I got 15s I wanted to go for SPL but my new box is going to be fiberglass so that my 15s almost conform to the sides of my car (like the 15s in the Alpine civic center seat demo car). In the back of Car Audio they talked about how they built the boxes for the civic and they ported them with the ports running lengthwise to the front of the car. Im looking to have a 1.5-2 cu.ft. enclosure for each sub but is that big enough to port? Im wanting to just build square ports and run them toward the front like alpine did...anyone done this and will it turn out ok?

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[Trixter 10+ year member]

I saw something like what your talking about before. The guy had two slot ports running under his seats and coming out at the front of them. (He was running 2 15" HX2's) that thing pounded! I guess you would build your box the size you wanted and you wouldn't have to worry about port displacement, so you could go with a smaller box. I'm not sure what size your A's want. I imagine ED's specs consider port displacement. If you could figure how big the box would be with out the port being inside of it, I'd say go with it. Or you could play it safe a talk to an ED tech.

 

[RcRacerDrew 10+ year member]

Yeah ED just has specs for sealed and vented...they recomend a certain vented box but they dont really give any specs for port area etc. I think Im just gonna play around with a few programs in a lil bit to get the port area I will need. Im hoping I can pull this thing off to keep each box at about 2 cu.ft. and run the ports from the side of the box under the back seat and out under it. Its an explorer sport....Im wondering if it matters how much the port itself bends or turns and to what degree....there will need to be some kinks in it to work and the alpine demo car had some kinks in its port to get it routed properly. All this is kinda new to me but hopefully this will work out!....I think Im gonna call ED too and see what they think.

 

[ramos 5,000+ posts]

It will work quite well. Just figure your box volume wthout port displacement. You will have to play with the port dimensions to get the tuning frequency your after. The box size is the hard part. It's kind of small for a 15" //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Trixter 10+ year member]

As long as the port stays true it shouldn't matter how many bends are in it. If you go square, make sure it stay square all the way through...the same with round (but it sounds like your going square)

Yah, contact ED, I got 1324sq" for a 2cu' box. That seems kinda high.

 

[RcRacerDrew 10+ year member]

Since it has to stay true maybe ill use a round port...PVC maybe? I just dont know how I would to the bends with PVC....PVC would be easier by far though. 1324 sq" ??

 

[Trixter 10+ year member]

Originally posted by RcRacerDrew Since it has to stay true maybe ill use a round port...PVC maybe? I just dont know how I would to the bends with PVC....PVC would be easier by far though. 1324 sq" ??

Just use PVC 90 or 45 elbows.

I'm not sure on the 1324. I got it by taking the lenghts of all the sides of the port (from the pic on the ED site) and X by 16" (the box's height)

The entire volume of the box is 3.29cu' - 2 (for the box) that leaves 1.29cu' for the port...if that helps at all

I'm not really sure. I suppose I could figure it out. But I'd feel better if you called ED.

 

[RcRacerDrew 10+ year member]

Oh yeah well Im gonna mess with figuring it out later tonight. Im not building my box exactly to the sites specs...Im just gonna build it in the room I have, as big as I can and see how much volume I wind up with..then Ill tune the port once I know that.

 

[RcRacerDrew 10+ year member]

Well I just messed around with WinISD and the results are great. According to its calculations and based off the specs on the Edesign site....A 15 in a 2 cubic' box with a 4" round port that is 10.34in long will yeild a very flat response and will be tuned at 35 hz. The graph shows the sound as being flat at 0 db from 500hz-50hz then it starts to slope down till it hits 20hz at -19 db. Im kinda new to this but that seem pretty right to me! Let me know what you think.

 

[Trixter 10+ year member]

Sounds like you got it. Personally I like a small peak (about +3db) right aroud the 30-32Hz area and then flat line. But it's all in personal taste.

 

[RcRacerDrew 10+ year member]

What does that do and how would I set that up?...also the port length dimension I got...Im assuming that is the length inside the box or would that work outside?

 

[Trixter 10+ year member]

Use WinISD. Try to set the freq. so you get a small peak around you desired freq. Then check the port dimensions. I set my to 26Hz to get a small hump at about 32Hz.

The port does not matter if it is in the box or out, it just matters on the area.

 

[RcRacerDrew 10+ year member]

Ok well I got that on lock down...now two last things for ya....does vent placement matter in relation to the sub and how much of the vent needs to sit inside the box or should it just be flush....anything I need to do so I can ensure there wont be any whistling?

 

[Trixter 10+ year member]

I have alway heard in the past that it doesn't matter where on the box you put the port. But a lot of people on this forum say it should go on the same side as the box. I really don't think that it matters, I have seen it done a ton of different ways, but you may want to check into that a little more.

As far a whistling goes, the bigger the port the less chance. For best results, for a 12" sub, a 5"-6" port is recommended. But the larger the port, the longer it has to be, so your going to have to find a happy medium.

The port doesn't need to be in the box at all. It will do the same purpose on the outside of the box as it will on the inside. The only thing you are trying to do is provide an amout of wind resistance to create a certain sound freq.

 

[RcRacerDrew 10+ year member]

well alright thanks!