NYCe MaXiMa

iTrader: (9)

I decided to build my own box..

I'm going to be using a single 12" image dynamics IDQ sub..

I bought a bunch of 3/4" MDF at home depot, now i'm looking to buy the rest of the things i may need...
i'm thinking of a ported box, it is more complicated to build but everyone advises i go with that...



Questions:

1) as far as calculations.. my sub is reccomended to be a 1.5 cubic foot box.. but what should the measurement be for ported one?

2) also.. where do i stick the port? which side?

3) any difference in the port opening tubes? which size should i use?



also, looking for any tips or info as far as building a ported box is concerned..

nupe500

iTrader: (13)

First you might want to contact Image Dynamics, to find out what size box you would need for a ported (usually its going to be larger, so you might not want to go that route) Also the port(s) can go anywhere...usually the side (pick one) And I believe that trhe folks at Image Dynamics could tell you what diameter port to use. I recommend the PCV from Home Depot...thats what I used a couple of years ago when I did a ported box...for my JLs

jmax

There are several free-ware box programs online. The best one I have found is WINISD Pro - http://www.linearteam.dk/

Aside from that the best sounding ports have flared ends. As in both ends are flared. But a compromise may be made by using a flare only on the end that exits the box. The larger the port entrance/exit surface area, the lower the speed of air in the port. When the air in the port reaches 5% the speed of sound or more, port noise is audible. So keep the port large enough to keep the air speed in the port below 17 m/s. Unfortunately the larger the port, the longer it needs to be to tune to the ideal frequency. That is why flared ports are ideal. The have a slight length increase over the non-flared version, but the sound characteristic of a larger port.

http://www.geocities.com/f4ier/vents.htm

And here is ID's site:
http://www.imagedynamicsusa.com/

To purchase flared ports see: www.partsexpress.com

Nore474

I was thinking the same thing because my old box is way too small and I want to make a ported one does anyone have a picture?

jmax

A picture of what? The port, the speaker, the ported enclosure?

Nore474

where do u reccomend on putting the ports

jmax

The side of the box isn't too important from an acoustical / phase relationship. Use the same rules that you do for maximizing spl and minimizing unwanted body panel resonance. Don't forget that the gross port volume must be subtracted from the internal enclosure volume. Also subtract sub and braceing displacement volumes from the enclosure volume. You need to have the internal enclosure volume measured as accurately as possible in order to tune the box / port / sub properly.

Example:
58 liter gross internal volume sub box
minus 4 liters for sub displacement, 1 liter for braceing, and 7 liters for port tube. Yields net volume of 46 liters. This becomes tricky because as the volume changes the tuning of the port changes.

A 58 liter enclosure tuned to 35 hz with a 4 inch round port requires the port to bu 10.5 inches long (2.7 l port). A 46 liter enclosure tuned to the same frequency requires a 4 inch round port to be 14 inches in length(3.6 l port). Now consider what happens if we want to extend the tuning freq down to 30 Hz for increased power handling at lower frequencies and increased sub bass output. The 56 liter box needs the port to be nearly 15.4 inches in length(4 l port). The 46 liter box needs the port to be just over 20 inches in length (5.2 l port). If you use flared ports add about an inch to the length of the port.

This is why it is important to calculate box and port dimensions before starting to cut.

bahmax

After you determine the proper diameter and length you need for your port(s). Parts Express has a decent selection of various sizes and types. If they don't have your size you can buy one too long and cut it down to size.

Brett

Maxima Dan

For a 12 inch sub you will need to go with at least a 4 inch diameter port anything less and it will cost you SPL. You might want to consider going with a slot port design. It allows you to make the same area port one inch shorter than the comparable round port, helps to brace the enclosure, and can be made to any length you want. See the JL audio tech pages for examples and calculations.

jmax

I don't know where you came up with the theory that a slot can be shorter than a round port of equal surface area. I would like to see the math for the calculations. Where you gain this mysterious one inch is not actually one inch. It is half the height of the port wall that shares an enclsoure wall. So a 5 inch square port would act like a 2.5 inch longer port. More spl and sq can be gained by flareing the ends of the port, but once again the port will need to be a small degree longer.

Nore474

I appreciate it guys thanks

Maxima Dan

Actually, the end correction factor is one half the width of your slot port. So, if you use a 2 x 15 inch slot port (Keeping under the golden 9:1 height to width ratio for a slot port), you will come up with a 1 inch reduction in port length.

jmax

1/2 the distance from the shared wall to the port wall that is parallel to the shared wall. When I think height I am thinking in a vertical manner. The floor being the shared wall.