Jag

hey guys..... i was going to port through my rear deck, my system will consist of a dd 9515d and a dei 1100d with a cap and xover. i need 4 or more cubic feet and i need to know if facing the sub into the opening of the cabin between the seat and trunk is the best way to face it along with porting through rear deck. i heard and seen a site where a guy faced the sub to the back ofa trunk car and ported through deck and it was loud with turnk open only(cancellation) so he turned it aroudn to the inside of the car and it was fine... i would need to seal the outside of the box and trunk so the energy put out by the speaker is put inside the cabinb only right??? in order to have the box sealed to the front of the trunk i would probably need to build it so the box will fit to the back, but probably not wide enough for both ports to fit in the box??? i mean that the back of the trunk has a certain width where it is touching the back wall but it is not as wide as the rest of the trunk, therefor im not sure that the width of the box i can fit to teh back of the trunk will allow me to port my box through the rear speakers?? anyone

Jag

anyone

jmax

Man, I don't think you even know what you are trying to do. I am pretty sure I know what you are trying to do, but do you? Did you really read the link I posted for you? What you are trying to do is essentially #1, squared. #1 was the worst sounding of the set-ups tried.

Also, how much do you know about tuning a sub box? In particular a ported sub? From you question about whether or not the port needs to be in the box, it sounds like you haven't read up on the subject. In this case, ask you questions much more slowly and as carefully as possible so that you can get answers that will assist you in making a good decision.

steeo

I have a ported box in my trunk with 2 x 12" subs in it and they are facing out of the trunk with the 2 ports facing up the way facing the speaker holes on the rear shelf and it sounds great. It does sound louder with the trunk lid open but the thump you get with the lid shut is unreal.

I thought you should feel subs rather than hear them + they look great at night time when I open the lid and there are 2 x 12" subs lit up by 2 blue neon lights and the digital readouts from the powercaps shining straight out at you

Jag

BUDDY... tuning a box will be done through something claled a PORT where i knwo the area from manufacturer and the formula is 2*Pi*R*H where h is also given sovle for r multiply by 2 u have a diameter for a certain freq. keep port big for greater freq and see how it soudn then keep cuttin it down untuil u reach desired freq. i dont knwo the squared **** ur talkin about but whateve rur sayin ill jus say no to that.. all i know if im facin the sub to the inside porting through rear deck

loudmaxima

ummm

jmax

Now let's try the correct formula:

Fb = 0.159 * sq-rt(Av(1.84 x 10 ^8) / (Vb(Lv + 0.823 sq-rt(Av))))

The formula you provided is for the volume of the port. Don't lose it because you need to subtract that volume from your sub box net volume to come up with a more accurate box volume. It is very important to have the actual box volume for determining port dimensions. Everytime you cut your port shorter, the tuning frequency will go up. The larger the port, the longer it needs to be to tune to a particular frequency. But like I said, you know all the formula's so you already knew this.

What I said was that you are taking a poor install decision and making it worse.

Jag

i dont think its a poort install decision because first it relieves trunk rattle and second it will create more bass output in the cabin. i am just trying to maximize the amount of bass that can be put into my car.

loudmaxima

4cu ft will be the majority of your trunk ,just do a subfloor, cut out the rear deck, and dynomat

Jag

what does ab vb, lb stand for. i think that off the jl site rite. i found that they give the area in inch^2 and i was finding vol in inch^3 so i cant use that to find my R how do i find out my radius of the cone if all i know is the area of port needed

Jag

whats a subfloor and cutting out the rear deck isnt that the same thing as sealing my ports through the speaker holes. it hink to figure out my r i would just have to use LxW where W is 2 radii and so say i use a 3 inch diamter port. Divide my area by 3 and thats the total lenght of port needed, can i do it this way... then plug it into my volume formula= 2*pi*R*h, r is half the W and h is the lenght port i just solved for.....

jmax

Av is cross sectional area of the vent in square inches.
Lv is the length of the vent, in inches.
Vb is the net volume of the box.

And yes, this is directly from the JL audio enlosure tutorials. You do not need the radius of the cone. Unless you are using the formula for minimum vent area for a given cone size. Unfortunately that formula is only good for average drivers. Speakers that can displace large volumes of air because of high excursion need larger vents than the formula's indicate, in order to eliminate or reduce port noise. Irecommend going to http://www.linearteam.dk/ and downloading winISD. A design software program that calculates the velocity of air with a chosen port area. You can choose whatever speaker, enclosure volume, and port cross sectional area. The program calculates the length of the vent and gives a mach rating to give you an idea how much port noise there will be. I think you want a mach rating of 0.16 or less. But the info is in the help files with the program.
Read your other post for the explanation of why it is unwise to put the box in the front of the trunk facing forward.
The only use of the volume formula you have is to determine the net volume loss of the port. You need to add that volume to your enclosure volume in addition to adding the volume of all braces and the drivers displacement. So if you have a speaker that displaces 0.15 cubic feet, a bracing volume of 0.10 cubic feet, and a port displacement of 0.11 cubic feet (3 inch diameter port with 1/4 inch wall thickness and 20 inch length) - you need to add this volume to your recommended enclosure volume. If the recommended ported volume for the tuning frequency that that would give is 1.0 cubic feet, you need to make the internal dimensiond of the box large enough for a volume of 1.0 + 0.15 + 0.10 + 0.11 = 1.36 cubic feet, or 2350 cubic inches.

Jag

to find the volume of my port for displacement purposes i need to know r and h r woudl be half of diameter. my friend is good with winisd thanx ill tell him about the port noise thing. i need area and volume area for how big the port is and volume for displacement

jmax

r, the radius is half of d, the diameter. pi * r ^2 is the area of the port. A good approximation of pi is 3.14. Multiply the area by the height for volume. But for displacement purposes use the external port radius to get the volume including the plastic or cardboard the tube is made of.