THOR450

Ok, here goes. I built a box for 2 JL audio 12w3's. It has approx. 1.4 cf per side and the port dims are 6.5"x2"x20". It sounds pretty good but I built the box so I can change to port length to suit my ears before I finish it up. JL calls for 1.75 cf per side and a bigger port. I was thinking of shortening the port by 6" to 14" and then putting the 6' I took from the port back into the box volume. It is a recatangular shape and has a few special areas to suit my vehicle. I know the shorter port should make the box be tuned to a higher hz and I have played with the port volume calculator. What are your opinions on shortening the port and putting it into box volume?? Which is more important? I listen to all kinds of music and had these same subs in a sealed box before, just trying to get some lower lows here.

Also, On Image dynamics site, they use poly fill matting on their ported boxes. It is the matted kind, not the loose stuff. It looks like they line the back wall of the enclosure and secure it with glue. Do you guys think that would help fool my subs into thinking they are in a bigger box?? Thanks again guys..

b34tBoX

What box calculator are you using, something doesn't seem right with that you are trying to achieve.


Do you have pictures of your box?

THOR450

Thanks b34tbox. My box fit under the rear seat of an extra cab silverado. I used all the space with raising the rear seat 2". My box is a recatngular truck box. What I was trying to say is I started with a 20 inch port by 2"x6.5"inches. My slot ports run the width of the box on the front and vent down to the floor. The woofers are downfire, so the woofers and the ports face the same direction. I shortened my ports to about 16 inches and used the other four inches back into the box for box volume. I put it together and tested it and it sounds good to me. Everything is sanded smooth ready for custom color. I am guessing my volume is close to 1.5cf. I noticed on the Image dynamics site that they used matted polyfill on their ported boxes and want to know what you guys think about that?? I am going to try it and see how it goes. My port dims are close and if the polyfill makes my woofs think they are in a little bit bigger box then it should be great. Comments?? Thanks!!

DeadlySones

iTrader: (4)

What are the dimensions of your box? Having smaller internal with a longer port is useless. The lows need the box volume to produce them lows. Then they need a big enough port to let them out. The trick is to balance them all. Otherwise, even though your tuning lower the actual response might begin to dip earlier.

eg. using your sub. White is JL specs, Yellow is your 1.4cu. Even though they are both tuned to 30hz, look how the smaller box starts to dip sooner. Smaller box also requires a longer port. In this case almost 5" longer.



This is same boxes @ 36hz tuning.



hmmm.... looks like the color isn't showing in the picture for some reason. It's there on my copy... anyhow, the lines on the right are yellow. Lines on the left are JL specs. Also notice that the box tuned to 36hz is about 1.5 db louder than the one tuned to 30hz.

There will come a point in tuning where the smaller box yields better results but thats in higher tuning. Say mid to upper 40's on up. If you give me your actual box specs I can play with it for you.

DeadlySones

iTrader: (4)

There is also more cone excursion in the larger box. Again, color disappeared, yellow line lower, jl specs upper.



Going by your port size, you'd need a 12.5" port for 36hz in a 1.75. It would be about 16.25 @ 1.4cuft to get the same tuning.

See where this is going? How much power are you giving these subs? If you have more power, you might want to stay around 1.5cubes. Tune it a little higher (provided you have a SSF) and use the extra space to allow for more port area.

Like I said, if you give me your box dimensions and how much power (what amp?) your giving them, I'll play around with the numbas.

DeadlySones

iTrader: (4)

x2. A couple pictures of the box would help. 1) in its installed position & 2) the side where the subs and ports are.

THOR450

N130Gv2 Thank you so far. I am following what you are saying so far. My camera is not available right now but Ill try to explain your questions. Rectangular box that fits the entire width of my Silverado extra cab truck underneath rear seat. Behind drivers door all the way over to passenger side. Subs fire down, slot ports face down towards the front of the truck from the subs. The box has many cuts and nook's to fit around things like seat supports and the transmission hump in the truck floor. I am guessing it to be closer to 1.5 cubic feet. 3/4 MDF glued and screwed. My amplifier is and old-school Soundstream reference 700 for the time being. This amp is good and clean for what is is. Right now my ports are 2 inches wide by 6.5 inches tall. These dims are fixed and I cant really adjust them because they are built into the box but I can adjust / tinker with the port length. Right now the port length is 16 inches. Thanks again for sharing!!!

DeadlySones

iTrader: (4)

Thats a good amp for them subs.

Edit: Just saw the 16" part. So your tuned to around 35hz currently. Knock it back to about 12" this will tune to around 38hz. The added volume should help it to play the lower notes a little better. The low internal volume/port area is starving the lower frequencies. Too bad you can't change the port area. Can you port to the sides of the truck?

THOR450

Ok, I cut the port length down to 13" inches. thats as short as I could go. I just got it all glued and sealed. Waithing to sand everything smooth again and then I will see how she sounds. Now on to my other question, I am planning to put a matt of the bonded polyfill in there. It is not the loose stuff, so there will not be an issue with blowing the filling out of the ports. Opinions on this?? Thanks

THOR450

N130gv2, Ok. I got the box back from being coated with line-X bedliner, secured the poly-fill matting inside, fitted the subs and tested the sound. I am very pleased with the sound. Definately goes lower than the previous sealed design and sounds fantastic. I am converted to a ported box guy now, never to return to sealed again!!!! Thanks again for your expertise!!