Port opening issue

[Gmansontos]

And I say port opening because port area to me is the total area of the port not just the area of the port opening. As this carstereo.com calculator states. Now this carstereo.com calculator says two 15 inch woofers with a 30mm xmax should have a minimum of 199 inches of area. (199 cubic inches of opening). Now I have a mid size SUV and I plan to build a ported box subs up and port rear. I've been told because I'm facing the port toward the rear that I can get away with some port noise as it would be hard to hear sitting in the front seat.

What I would like to know is...is this calculator on carstereo.com..... http://www.carstereo.com/help/Articles.cfm?id=31 accurate and how much under their recommendation can I go before the port noise gets to be too much.

[Triticum Agricolam]

What you are calling port area is what the rest of the world calls port volume. Port area is a 2 dimensional measurement and is measure in square inches, port volume is 3 dimensional and is measured in cubic inches/feet/etc.

Yes the port calculator at carstereo.com is accurate. You can get away with a little less port area, but just how much less is very situation dependent. If you want a better answer you can model your sub and box in something like WinISD or the like and see what your port velocity will be based on how much power you are going to run.

[magillaru]

Not to confuse you or disagree with triticum but when I was designing my box, I was thinking the same thing about carstereo's recommendations for minimum port area. I was told by two different people, one being a reputable box designer on here that it was much higher than it needed to be.

I ended up going by what was recommended to me by the subs manufacturer rep.....my port area was significantly less than what was recommended by carstereo.

And even then, I was told by another person that they would've probably gone with a little less but it was more of a personal preference.

Again, I have only one box design/build under my belt....just sharing a few things I found out during my process.

[Triticum Agricolam]

Hey Magillaru, what subs and box specs did you go with, just out of curiosity.

To the OP, proper port area is a question that has no easy answers. One thing I can tell you is the disadvantages of port that is larger than it needs to be (within reason) tend to be much less significant than the disadvantages of port that isn't large enough.

[magillaru]

2 fi team 15s with 120 sq in of port

....like I said, this is in the ballpark of what was recommended to me.

Based on the info I got, there's a flaw with how some of the online calculators work with subs having such a high xmax.

***would like to state again, this is just what was explained to me......I'm in for any new info/discussion on this.

[Triticum Agricolam]

2 fi team 15s with 120 sq in of port

....like I said, this is in the ballpark of what was recommended to me.

Based on the info I got, there's a flaw with how some of the online calculators work with subs having such a high xmax.

***would like to state again, this is just what was explained to me......I'm in for any new info/discussion on this.

I wouldn't say there is a flaw with the calculators and high xmax subs, its more they operate on an assumption that isn't always true. Those calculators assume you are going to push the sub to its xmax, and if you did the amount of area they recommend would probably be appropriate. The problem is subs these days have such huge xmax that you will probably run out of power handling capacity before you reach xmax. Obviously this depends on box design though.

What size/tuning is your box and how much power are you running on?

If we take the FI TEAM15's and put them in a 10 cube box @ 32 Hz on 8K watts, your excursion is only going to get to about 20 mm above 30 Hz. Below 30 hz it starts to get crazy, but let assume the subsonic filter is set appropriately to keep things under control. So with only 20 mm of excursion you wouldn't need as much area as the calculator tells you you do.

[magillaru]

I guess "flaw" was a poor choice of wording.

Great explanation though.....thanks! That makes much more sense now.

My net volume came out to ~8.4 tuned to 32.5 hz and will be running them on one AB 1100.1 hoping to see around 10k.

I have a build log on here if you want to check it out.

[Triticum Agricolam]

I guess "flaw" was a poor choice of wording.

Great explanation though.....thanks! That makes much more sense now.

My net volume came out to ~8.4 tuned to 32.5 hz and will be running them on one AB 1100.1 hoping to see around 10k.

I have a build log on here if you want to check it out.

Hey I just looked through your build log. Your setup looks great! I'm sure it pounds!

I plugged all your box specs into WinISD, based on what it said you may benefit from a little more port area, but who knows. A lot of it depends on just how much power you actually end up getting out of your amp. Things like impedance rise and power compression make that a tricky thing to know w/o something like an AMM-1.

If you want to know for sure if your getting port compression, you can test for it if you have access to an AMM-1.

[Krakin]

I've still not had anyone prove to me or seen anybody prove that you can have an adverse affect from large amounts of port area, if I recall correctly Triticum and I once talked about exceeding past cone area.

I still stand by the Small calculation for getting the amount of port area necessary to have minimal disturbances in air flow based on area.

This doesn't always mean that you will have a higher SPL, but I have set gaining SPL (for a daily build and all except for non-drivable vehicles) from port compression at the bottom of the list of priorities.

I still don't even like wave manipulation for output.

[hoit]

tuned in for knowledge!