Calculating port area with xmax?

[shanesauce]

Excuse me for the noob question but I saw something the other day in one of these threads about calculating port area of a box with the xmax of a sub?

I know the standard is 12-16 per foot but this person was swearing that was the wrong way to go about it.

Can anybody help me out and explain this forumla and why it will yield a better sounding box?

[Rockford96]

Your excactly right I can't answer the question because I don't know but I'm pretty sure it has to do withthe xmax and cone area of the sub I think I know the loudspeaker cookbook has a lot of good reading in it for this

[Krakin]

you can use these formula's:

http://www.carstereo.com/help/Articles.cfm?id=21

http://www.diysubwoofers.org/misc/portcal.htm

Or this calculator for quick references.

http://www.carstereo.com/help/Articles.cfm?id=31

[shanesauce]

you can use these formula's:

http://www.carstereo.com/help/Articles.cfm?id=21

http://www.diysubwoofers.org/misc/portcal.htm

Or this calculator for quick references.

http://www.carstereo.com/help/Articles.cfm?id=31

Okay, so with that calculator I entered (2) 8" drivers with a xmax of 16.5mm one way @ 32 hz and it told me 27 inches of port area?!?

This seems to be a bit odd, could someone verify this? And would that 27 inches of port be per cube gross or net?

[Krakin]

It's not per cubic foot, just straight 27 sq inches.

[shanesauce]

It's not per cubic foot, just straight 27 sq inches.

Thanks for the quick response, I was about to crap myself trying to fit so much port into such a small box...

[Triticum Agricolam]

Hey Shane, it was probably me you saw saying the whole 12-16 sq. in. per cube is the wrong way to do it. Actually its not that is necessarily wrong, its just not the best way to do it. The links Krakin posted will get you pointed in the right direction. If you want to see where I learned about it you can see it here at the bottom of the page: https://www.trueaudio.com/st_ventq.htm

[shanesauce]

Hey Shane, it was probably me you saw saying the whole 12-16 sq. in. per cube is the wrong way to do it. Actually its not that is necessarily wrong, its just not the best way to do it. The links Krakin posted will get you pointed in the right direction. If you want to see where I learned about it you can see it here at the bottom of the page: https://www.trueaudio.com/st_ventq.htm

If I remember correctly it was a guy that had a speaker as his picture, I know that doesn't narrow it down too much lol.

But thanks again for the information guys, what is crazy is the gross on this box is 2.5cuft and the net I end up with after port is 1.37!!!

A 3" wide port and 58 inches of port length is a lot to fit into a box for 2 8's!

[Rail]

Hey Shane, it was probably me you saw saying the whole 12-16 sq. in. per cube is the wrong way to do it. Actually its not that is necessarily wrong, its just not the best way to do it. The links Krakin posted will get you pointed in the right direction. If you want to see where I learned about it you can see it here at the bottom of the page: https://www.trueaudio.com/st_ventq.htm

If I remember correctly it was a guy that had a speaker as his picture, I know that doesn't narrow it down too much lol.

But thanks again for the information guys, what is crazy is the gross on this box is 2.5cuft and the net I end up with after port is 1.37!!!

A 3" wide port and 58 inches of port length is a lot to fit into a box for 2 8's!

That would be me. Thats a picture I took of my Fi SP4.

Anyways, the 12-16 sq in per cube is wrong. Its only that it sometimes happens to be close to the correct amount of port (usually when you get closer to 16sq in per cube). But it is still not the way to do it, port area depends on the subwoofer(s) and the tuning frequency, each subwoofer is designed differently and will need its enclosure to be designed differently. The enclosure has a HUGE effect on the performance of a sound system. And also you say that your net volume is 1.37 cubic feet, that should be right about what you want depending on the subwoofers. Most 8" need about .5 to .75 cubic feet each correct?

[shanesauce]

Hey Shane, it was probably me you saw saying the whole 12-16 sq. in. per cube is the wrong way to do it. Actually its not that is necessarily wrong, its just not the best way to do it. The links Krakin posted will get you pointed in the right direction. If you want to see where I learned about it you can see it here at the bottom of the page: https://www.trueaudio.com/st_ventq.htm

If I remember correctly it was a guy that had a speaker as his picture, I know that doesn't narrow it down too much lol.

But thanks again for the information guys, what is crazy is the gross on this box is 2.5cuft and the net I end up with after port is 1.37!!!

A 3" wide port and 58 inches of port length is a lot to fit into a box for 2 8's!

That would be me. Thats a picture I took of my Fi SP4.

Anyways, the 12-16 sq in per cube is wrong. Its only that it sometimes happens to be close to the correct amount of port (usually when you get closer to 16sq in per cube). But it is still not the way to do it, port area depends on the subwoofer(s) and the tuning frequency, each subwoofer is designed differently and will need its enclosure to be designed differently. The enclosure has a HUGE effect on the performance of a sound system. And also you say that your net volume is 1.37 cubic feet, that should be right about what you want depending on the subwoofers. Most 8" need about .5 to .75 cubic feet each correct?

Yes, you are the one I was referring to but I couldn't find the thread that you posted in.

I preach to all of my not so audio savvy friends that the box makes the build but of course they don't listen.

I am at 1.37 net with 1.2 after subs and the SA-8's like 0.5-0.6 according to Jacob. Port is at 27 square inches and 52 inches long if I remember correctly.

Just curious do aero ports still get the same treatment in terms of needing less port area?