Ported Box Parameters
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=89504
Printed Date: May 02, 2024 at 6:17 AM
Topic: Ported Box Parameters
Posted By: lilj2343
Subject: Ported Box Parameters
Date Posted: January 24, 2007 at 7:39 PM
I was wondering if anyone out there could help me to design the perfect box for my Audiobahn Alum15n..... I'm wanting to install in the back of a 2000 Grand Prix GT using 3/4 inch MDF and can't really decide if i want to get a box built, (costing me 350.00) or just doing it myself, so if i at least could get some good measurements on how to build the right box, it would be really helpful. The requirements that the audiobahn website calls for are as follows......
3.5 ft3 air space
Port size = 2 at 4 x 10.5
Port vel = 23.25 (and what is this exactly)
Sub disp. = 0.25 ft3
Port disp. = 0.14 ft3
Total Volume = 4
Thanks for any help you guys can offer, i have been to this site numerous times and i am continuously amazed at what you guys know about this stuff.....
Replies:
Posted By: stevdart
Date Posted: January 24, 2007 at 9:02 PM
To help you decipher that info: - Net air space, inside the box, dedicated for use by the woofer. This is the volume of air after all displacements are subtracted.
- Two 4" round ports, each at 10.5" long. This design apparently calls for two ports for a couple of reasons: one, to increase the port opening area to eliminate port noise, and two, to increase the length of the port. Two 4's often fit better than one 6" on the box.
- Probably velocity of the port air measured in feet per second. If so, this is a good low number. If it is meters/sec, it is high (but within reason). Low is better. Whatever it means, I'd say that with the two 4" ports you will be fine as far as port noise goes. (It's odd that this is shown with a decimal place. Usually whole numbers are used when speaking of calculated port velocity.)
- The actual displacement of the driver when "top-mounted" through 3/4" construction. This is the normal mounting for subs; not recessed. The driver part that sticks into the box takes up airspace, and that is what is shown. There's a lot of junk on that sub by the looks of that number (it's high).
- The displacement of the two 4" ports when mounted through the baffle. These displacements are calculated into the total inside airspace so that you finally end up, when all is considered, with the net air space shown in the top line.
- Total volume = 4 makes you scratch your head when you do the math, but that is what they are telling you to start off with, in interior cubic feet volume. By the time you install the ports, the driver, and maybe whatever bracing they have detailed in the design, you should end up with 3.5 cu ft net.
The tuning frequency appears to be approximately 36 to 38 Hz.. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: lilj2343
Date Posted: January 24, 2007 at 10:56 PM
that helps me to understand the meaning of all of it....thanks. i was wondering if there was some way i could find out exact specs for a box for the sub though..... so that all i have to do is measure it all out, cut, and put it together... i suck at math thats why i'm looking for the easy way out!!! Thanks
Posted By: stevdart
Date Posted: January 25, 2007 at 6:49 AM
Use a pencil and paper and do a lot of rough sketching. Start by measuring the available space in your car where you want to put the enclosure. Use a steel tape measure and get the measurements in inches. You'll have to know width or side-to-side, depth (front to back), and available height. These three meausrements multiplied will give an answer in cubic. If you multiply inches, you'll end up with cubic inches; if you multiply by feet you'll have cubic feet. 12 x 12 x 12 = 1728........the cubic inches in one cubic foot. When you have a good idea of how much room you have to work with, go to the help section of this site: https://www.the12volt.com/caraudio/boxes.asp and https://www.the12volt.com/caraudio/boxcalcs.asp If you intend to use 3/4" MDF for the box, enter .75 in the box that calls for "thickness". Play around with some numbers in these boxes that are within the parameters of space that you already measured in your car; that is, each time you try a combination, be sure it will fit into your available space. See what meaurements you can arrive at that will work in your situation and make the box size appropriate for your project. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: lilj2343
Date Posted: January 25, 2007 at 1:04 PM
thanks again........i didn't even know about the calculation page the site has so now i'm gonna use it instead of asking a "newb" question like this....
Posted By: stevdart
Date Posted: January 25, 2007 at 9:40 PM
Posted By: lilj2343
Date Posted: January 28, 2007 at 3:10 PM
thanks a lot man..... i went up to the most respected audio place in my area yesterday and the owner wants to take me "under his wing" so to speak and teach me because he said it's nice to see someone my age actually interested in the art of audio......and i'm 19 so this is an awesome opportunity for me.... i appreciate everything!!
Posted By: stevdart
Date Posted: January 29, 2007 at 5:26 PM
That's cool. Good luck!
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: youngblood
Date Posted: January 30, 2007 at 1:05 AM
I enjoy seeing people like stevdart go out of their way to provide as much information as they do. Appreciate the links. I'm interested in the importance of the "tuning frequency" when building a box. What's is optimum?
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