Port selection help

[dangaranga]

Now i already made a thread looking for help in the C2 audio section and i really hate to make another thread but it doesn't seem to be getting much in the way of attention. Anyway, I have a Threatcon-2 12 in a 2.12 cu box and i am looking to redo my aero ports because i currently have two 2-5/8" by 12'' ports atm and i feel that there is nowhere near enough port area and tuned way too low

What would be recommended as far as port area to keep this sub happy? I was thinking of going to a single 4"x 10" port which is about 35.83hz and 12.57 in2 of port/ or 6.16in2 of port per cu ft.

Thanks

[David Bailey]

Did you try to e-mail C2 audio? I am sure they would give you some info.

[dangaranga]

Honestly, it didn't occur to me lol, I'll e-mail them in the morning, Thanks

I will update the thread with their recommendations incase someone else has the same question

[dangaranga]

So I emailed C2 and to my shock Chris had responded within like 15 min (big cudos to him!!) and recommended to tune to 32hz for daily and also recommended this tool to calculate the port dimensions.

[Joe X]

So I emailed C2 and to my shock Chris had responded within like 15 min (big cudos to him!!) and recommended to tune to 32hz for daily and also recommended this tool to calculate the port dimensions.

That tool can help you with tuning but will not help you with the port area.

[dangaranga]

Ok i'm all open for any ideas/help, any suggestions Joe?

[Bryan Maynard]

Although everyone on here may not agree with me, this is how I figure out my ports...

I like to keep my port diameter between a third and a half of the diameter of the subwoofer. For example, an eight inch subwoofer would require a port diameter somewhere between two and four inches--or between 3.14 and 12.57 square inches of port area. Now, obviously, a two inch port is not going to work for a high output subwoofer without port noise, but you can still choose up to a four inch diameter port with this method. The thing to keep in mind when going with a bigger port, or more "port area," is that the length of port will increase dramatically. In keeping with our "example" eight inch subwoofer, lets assume that that particular speaker needs a net volume of 0.75 cubic feet, and a tuning frequency of 35 hertz. For these general specifications, a two inch port would need to be 7.75 inches long, a three inch port would be 18.54 inches long, and a four inch port would be 33.939 inches long. So, Your space requirements, and your need for an absence or port noise are both factors in deciding what size of port to use.

The next concern I deal with is converting "port area" into a round port diameter; this is important so that you can properly calculate the length of your slot port--if that is what you are going to use. Now lets say that I have twelve square inches of port area. There are three steps to convert that, or any other port area, into a round port diameter. First, divide the port area by 3.14 (pi). Second, take the resulting number and find its square root. Third, multiply that number by two. If we follow these three steps, we see that twelve square inches of port area gives us a round port diameter of approximately 3.908 inches.

The last step in calculating ports I use is to figure out the vent length and their displacement. The formula for figuring port length is as follows:

2117(D)^2

--------- - 0.732D

Fs^2 x Vb

(D)^2 is the diameter of the port, squared

Fs^2 is the tuning frequency, squared

Vb is your net airspace

D is the port diameter

Now, it doesn't really matter what shape (within reason) that twelve square inches of port area is in for the port length equation, just that you properly converted port area to round port diameter. Once you have the information you need to calculate the length, the job is as easy as plugging numbers into a calculator. Finding the displacement of a port is just as easy. A round port's displacement is calculated by squaring the radius of the outside diameter of the port, multiplying that number by pi (3.14), multiplying that result by the length, then dividing that number by 1728. A slot port is calculated by multiplying the outside height and the outside width together, then multiplying the result by the length, and finally dividing that number by 1728. I know it sounds like a lot, but its important to get those calculations right, so that tunings and airspace aren't thrown out of whack.

Like I said before, everyone may not agree with me on this subject--and that is okay; but from my experience, this process works really well, when calculating port area and length. If you are unsure about the amount of port area, you can find an online tool that calculates vent mach; and if memory serves me correctly, anything over 0.1, will cause port noise. Remember, if you do use the method I outlined, follow these steps:

+ Keep the port diameter between one third and one half of the subwoofer's diameter.

+ If using a slot port, convert port area into round port diameter.

+ Use the port length equation to calculate proper length for intended tuning.

+ Find, and add, port displacement to keep final tuning.

I know this post was long, but I hope that it helped; thank you for reading it, and have a nice day.

[dangaranga]

Although everyone on here may not agree with me, this is how I figure out my ports...

I like to keep my port diameter between a third and a half of the diameter of the subwoofer. For example, an eight inch subwoofer would require a port diameter somewhere between two and four inches--or between 3.14 and 12.57 square inches of port area. Now, obviously, a two inch port is not going to work for a high output subwoofer without port noise, but you can still choose up to a four inch diameter port with this method. The thing to keep in mind when going with a bigger port, or more "port area," is that the length of port will increase dramatically. In keeping with our "example" eight inch subwoofer, lets assume that that particular speaker needs a net volume of 0.75 cubic feet, and a tuning frequency of 35 hertz. For these general specifications, a two inch port would need to be 7.75 inches long, a three inch port would be 18.54 inches long, and a four inch port would be 33.939 inches long. So, Your space requirements, and your need for an absence or port noise are both factors in deciding what size of port to use.

The next concern I deal with is converting "port area" into a round port diameter; this is important so that you can properly calculate the length of your slot port--if that is what you are going to use. Now lets say that I have twelve square inches of port area. There are three steps to convert that, or any other port area, into a round port diameter. First, divide the port area by 3.14 (pi). Second, take the resulting number and find its square root. Third, multiply that number by two. If we follow these three steps, we see that twelve square inches of port area gives us a round port diameter of approximately 3.908 inches.

The last step in calculating ports I use is to figure out the vent length and their displacement. The formula for figuring port length is as follows:

2117(D)^2

--------- - 0.732D

Fs^2 x Vb

(D)^2 is the diameter of the port, squared

Fs^2 is the tuning frequency, squared

Vb is your net airspace

D is the port diameter

Now, it doesn't really matter what shape (within reason) that twelve square inches of port area is in for the port length equation, just that you properly converted port area to round port diameter. Once you have the information you need to calculate the length, the job is as easy as plugging numbers into a calculator. Finding the displacement of a port is just as easy. A round port's displacement is calculated by squaring the radius of the outside diameter of the port, multiplying that number by pi (3.14), multiplying that result by the length, then dividing that number by 1728. A slot port is calculated by multiplying the outside height and the outside width together, then multiplying the result by the length, and finally dividing that number by 1728. I know it sounds like a lot, but its important to get those calculations right, so that tunings and airspace aren't thrown out of whack.

Like I said before, everyone may not agree with me on this subject--and that is okay; but from my experience, this process works really well, when calculating port area and length. If you are unsure about the amount of port area, you can find an online tool that calculates vent mach; and if memory serves me correctly, anything over 0.1, will cause port noise. Remember, if you do use the method I outlined, follow these steps:

+ Keep the port diameter between one third and one half of the subwoofer's diameter.

+ If using a slot port, convert port area into round port diameter.

+ Use the port length equation to calculate proper length for intended tuning.

+ Find, and add, port displacement to keep final tuning.

I know this post was long, but I hope that it helped; thank you for reading it, and have a nice day.

Ok so this is what i have, a single 4'' aero port from Precision port, the box is 2.12ft³ gross, and 2.01 after port displacement NOT including sub displacement. As for the port i've come up with a final tune of 31.85hz with the 4'' aero and 13.67 inches flare to flare. port area is 12.57in² and port displacement is .11ft³

^{Does that seem good? did you happen to know a reputable calculator to find the vent mach?}

[Bryan Maynard]

does the manufacturer say to add the sub displacement into the total box space, or to not worry about it, because that displacement could make a difference in the final tuning frequency. I'm not too familiar with aero ports but for a regular round port, it sounds good. as far as vent mach calculators, I use WiniSD to design my boxes, and it has a vent mach calculator in it. another option you have is to make the port removable; you can do this by building a recessed mount in the box where you want the port to go. then each port you try is attached to its own peace that is screwed into the recessed mount you made. Doing this would allow you to physically here the port noise, without having to see a number to know if a port is good or not. A lot of people make interchangeable ports as a way to see what frequency will be loudest in their vehicle too.

[dangaranga]

These are the specs from the website, i can e-mail them to see if they have the displacement info

12" Threatcon-2 Dual 2 Ohm

FS: 36.4 Hz
VAS: 37.1 L
QES: .46
QMS: 4.56
QTS: .42
Le: 1.84 mH
BL: 19.0
MMS: 182.2 g
SENS: 88 DB
XMAX: 28 MM

Woofer Dimensions:

EXT DIA: 12.48"
CUT OUT DIA: 11.18"
MOUNT DEPTH: 5.82"

I found this calculator http://www.linearteam.dk/default.aspx?pageid=ventcalculator

and it says the vent mach is 0.02