Calculating port area with xmax?

[Triticum Agricolam]

OK I'm seeing a reoccurring theme here guys so I'm going to set you straight. Two 3" ports does NOT equal one 6" port, not even close. What we care about here is not port diameter its port area. A 6" port has 28.27 square inches of area, so if you use smaller ports you will need enough of them to equal that amount of area. If you use 3" ports you will need exactly 4 of them to equal one 6" port.

So basically if you use a port half the diameter you are going to need 4 times as many of them. This applies to you too alaskanzx5. Two 7.25" ports won't work for what you want to do.

[alaskanzx5]

So basically according to that website I'll have to have roughly 3-4 6" Ports? That's sucks, I don't have enough surface area on the box for something like that....

19" tall x 19" deep x 40" wide subs up facing in a hatchback port any.direction besides up wouldn't give the Ports.room to breath.

[notorious97200]

I don't want to be...offensive, but if you can't calculate the area of a circle, you should not try to design a box with round ports.

Some people are good at designs, on this forum. Personnally I use ram-designs (I was a maths teacher!!!), but there are others too. It's cheap and efficient.

Good luck

[notorious97200]

Double post
Sorry !

[Triticum Agricolam]

So basically according to that website I'll have to have roughly 3-4 6" Ports? That's sucks, I don't have enough surface area on the box for something like that....

19" tall x 19" deep x 40" wide subs up facing in a hatchback port any.direction besides up wouldn't give the Ports.room to breath.

This is why I very rarely use round ports. If you do a slot port you can pretty much make it any size you need. Its still going to eat up a bunch of your box volume though, not much you can do about that.

[alaskanzx5]

I'm already low on volume though with no more room to make the box bigger.... I could port forward with the Ports at the bottom of the box but then they would only have the needed room when the.seats are folded down and I could only go up to like 13" long ports

[Triticum Agricolam]

I'm already low on volume though with no more room to make the box bigger.... I could port forward with the Ports at the bottom of the box but then they would only have the needed room when the.seats are folded down and I could only go up to like 13" long ports

13" long ports are not going to work, unless you want to tune it really high. Most ports are going to be in the 24"+ long, some a lot longer.

Making things fit is probably the hardest part of designing this stuff. The standard rule applies here: "You make make a box that's loud, hits low, or is small. Pick any two you want."

[alaskanzx5]

I guess I'll just stock with the plan and hope for the best not trying to break any records.anyways.

[shanesauce]

OK I'm seeing a reoccurring theme here guys so I'm going to set you straight. Two 3" ports does NOT equal one 6" port, not even close. What we care about here is not port diameter its port area. A 6" port has 28.27 square inches of area, so if you use smaller ports you will need enough of them to equal that amount of area. If you use 3" ports you will need exactly 4 of them to equal one 6" port.

So basically if you use a port half the diameter you are going to need 4 times as many of them. This applies to you too alaskanzx5. Two 7.25" ports won't work for what you want to do.

So then if this is the case why is the calculator telling me a minimum of 6 inches port diameter? Does this mean minimum in terms of smallest port one can be?

I was calculating wrong on the port area, I was only multiplying the diameter by 3.14 and not the radius squared.

So in order for me to get the correct tuning and I need a 6 inch aero for roughly 28 inches of port area and 42 inches of port in length... This is ridiculous trying to fit all this port.

I would have just went with my original slot port but it is also so long that the sub closest to the port will have unloading issues...

KILL ME PLEASE

[Rail]

Just to make sure - the formulas use Vd. That is the peak to peak swept volume, not one way Xmax.

I think your minimum calculates to 55 sqin, unless I misunderstood something.

In a car, you don't really have to have that much. The port may not operate 100% correctly at maximum driver excursion, but it will work.

Yes, an aero can have less port area. It eliminates a significant amount of port noise. Once again, the port may not operate 100% correctly, but as long as you don't get so small that the system begins to act like a leaky sealed box instead of a ported box, it will be fine.

I would guess ~30-35 sqin is enough for that pair of subs. Or you might could get decent results with one 4" aero.

Vd is only measured as displacement from the resting point of the cone, peak to peak/total throw is not used to calculate Vd. Also if you want to be very particular, Small's formula defines xmax as coil overhang, which is not the parameter most manufactures list. Most manufactures list xmax at 70% BL. For a sub with a 30mm xmax, overhang will be roughly 22mm, but this varies for every subwoofer. So if you use the xmax rating at 70% Bl you will get a slightly conservative answer. And you don't need less port area if you use aeroports, a port is a port and you will need the same area regardless. For this reason I find it easier to just do one large slot port.

So in order for me to get the correct tuning and I need a 6 inch aero for roughly 28 inches of port area and 42 inches of port in length... This is ridiculous trying to fit all this port.

I would have just went with my original slot port but it is also so long that the sub closest to the port will have unloading issues...

If you are having trouble with the port then instead of having the slot port follow the walls of the box, why don't you have it double back on itself?

And here is the link to the thread that you mentioned you couldn't find

http://www.stevemeadedesigns.com/board/topic/177996-how-much-port-area-for-an-18/