Ok so just working out a few things for the CAA SPL Project, doing some preliminary plans for space issues.

Anyway I'm looking at the amount of area needed for our port. As I think you all know we will be running a total of four Total Recoil 15's. Now I'm aware that most of the top SPL vehicles are running a port area vs speaker area ratio of 1:1 (Is this correct or is there a slightly larger ratio now?) Either way I'm wondering about clarification as to how the speaker surface area is calculated. I know the whole (Pi*R2) calculation but what is unclear is the determination of the diametre of the sub. Is this done by the physical size of the sub IE 15" or rather by using the actual radiating surface area (in our case 12.5") The differences are quite signifigant once you consider you need to multiply this result by the total number of woofers (in our case 4)

For example if we use the 15" diametre we need 4.90625ft2 of port area, but if we use the 12.5" radiating surface area we only need 3.4071172ft2 of port area.

I'd be inclined to go with the larger one seeing as we can always make the port area smaller...

Opinions or better yet links to related discussions/results...

Thanks for the help.
Scott

I'm assuming Xmax and moving mass would have a HUGE affect on this.

No point having a huge port if the moving mass and Xmas are not great enough.

If you catch my drift.

What sort of subs are they using with a 1:1 ratio? high Xmax DD's and the likes? I'd image that boyds 15" Xmax wouldn't be close to that sort of woofer, in terms of comparison.

For walled cars, 1:1 port is highly recommended. We are yet to get to the stage where we play with that, can't wait...

Anyhoo, you want the effective surface area of the cone, which IIRC is often taken as 1/2 the surround + cone area (so diameter is measured from 1/2 in the suround on one side, to 1/2 way in on the other).

AS MUCH AS YOU CAN GET. thats pretty much what you want

yes normaly 1:1 but extreme cars are not normal so get as much as you can, and by the looks u will need to have port where ever u have a space on the wall in the mini.

[ December 11, 2002, 12:30: Message edited by: KraSE ]

*cough* tubes *cough*

Anyway, I looked up one of dB Dons great posts on this subject:
http://makeashorterlink.com/?R5E012AB2
(make a shorter link used coz these boards go spacko with forum links...)

It mainly applies to SS vehicles, but ex is fairly similar.

"thats right......you cant have too much port area unless your note goes above 80hz! " Quote from Mike Hughes

definately as much as you can, which wont really be much in the mini, i dont think.

my new street 3-4 car has 800Sq inches

cone area wise, 15"s generally have around 120-140 sq inches, although with the high excursion subs you get these days, it is around 120-130 sq inches...

As far as port area goes, it depends on how much air needs to be moved through the port..

Icebreaker is on the right track when he mentions xmax and mms, but it depends on the note, as well as the actual efficiency (Mms, Bl, Re, Vas and box size are all needed) as well as the amount of power.. (also, if the impedance at the note is at least double and you are loading down the amplifier, then assume twice the power..

Also keep in mind that with a large amount of power, there will be a degree of thermal compression.. Also, some subs have far more useable excursion than their "linear xmax" (even though the sub will be suffering from a degree of compression due to the drop in BL and Cms).

1:1 is a good start, but for setups with 10kw+ at resonance (even more once you take into account the loading down of the amplifiers) per sub, you will want a lot more..

So getting back to the orif=ginal question is the measurement taken as the effecive radiating surface similar to what The Kid said?

IE 1/2 of one surround acroos the woofer to 1/2 the other surround?

If so we would be at 12.5" diametre...
Therefore could easily go to a ratio beyond 1:1

yes.. if you do the math, it equals about 123 sq inches