Here is the New Delema... Calculating the length of this port (to get 40hz) using the circular diameter of 5.12 I have gotten a couple of extreme differences depending on the site you go to... Here in th 12volt site... ( 12 volt site ) I entered the port diameter of 5.12 the cubic measurement of the box =ing 4cfeet and the desired frequency responce of 40 hz. Here it says that the length should be 8.67257" . On this other site ( carstereo ) using the same numbers it gives me a significantly different port length of 4.92" So whats the Dilly... My project is a '97 Acura CL... I am Putting 3 10" subs in the rear Deck under the window and porting the box through the arm rest hole that goes all the way into the trunk! 3 HE2 RFP4210 ( speaker specifications ) Xmas of .51 inches or 13mm, In a 4 cu. ft. box the port size has been determined to be 5.12 circular diameter or 4.59-.60 in. sq. (square port) I have figured the resinate frequency of the car to be right around 40hz using this equasion in Figure 4b ( Figure 4b ) The speed at witch sound traves is converted into inches rather than feet. measurements from the box to the wall will be 84 inches. if you divide the 13560 inches by four ( to use only a 1/4 of the waveform) you get 3390 inches per second... Then you divide that by 84 and you end up with 40.3...Hz. And thus why I want to tune the box to 40hz. Any takers...dont be scurd! Help please!

 

OK figure this... If you have a box that is 1.33 cu. ft. and a port that is 2.65 x 2.65 square and you are tuning the box to 40hz you get an answer of 6.71 inches for a port length using carsstereo.com... Then exactly trippling these measurements, going to a 3.99 cu. ft. box and using a 4.59 x 4.59 square port and tune it to 40 hz. you get a measurement of 5.11 for the port length. This is where I am totally lost. What is the deal here the measurements, I thought should be exactly the same. Why is this wrong/ different. If I can answer this question I can figure out the equasion!

 

Ok, whatever box you have for one, triple the volume. Whatever port VOLUME for one, triple it for all three. Forget this stupid shit you are doing with the area of the opening (See my post in your other thread).