Port length calculator

[bigrank916 72]

So Im designing a new enclosure and have come across a speed bump.

Using the12volt slot port length calculator with these numbers: 24, 4, 6.13, 32= 33.13in

Using carstereo.com port length calculator with the same numbers for a square slot port= 21.13in

But when you change the option of slot port from yes to no, the new calculation is exactly 33.13in

Why do they not match for the same thing? Shouldnt a square vent be shorter than a slot port? Did carstereo.com just flip flop them or something? Am I taking crazy pills or what?

[NB50 206]

Looks to me like its a effective length problem.

12V is giving you the length with effective length added on and CS is not. That is why you are getting 21.13 with yes selected and 33.13 without it selected. It is adding half the port length with yes selected and not showing it.

[Cinnabun187 2]

i'm using 12volt for my enclosure are their calculations accurate?

[bigrank916 72]

i'm using 12volt for my enclosure are their calculations accurate?

I know the gross enclosure volume is correct. The others have me wondering.

I want to ditch the slot and just go with a square vent.

[bigrank916 72]

Looks to me like its a effective length problem.

12V is giving you the length with effective length added on and CS is not. That is why you are getting 21.13 with yes selected and 33.13 without it selected. It is adding half the port length with yes selected and not showing it.

Im sorry but this is confusing. Maybe Ive been thinking about this for too long and not seeing something in the right light. Uuggghhh...

[Impious 1,476]

So Im designing a new enclosure and have come across a speed bump.

Using the12volt slot port length calculator with these numbers: 24, 4, 6.13, 32= 33.13in

Using carstereo.com port length calculator with the same numbers for a square slot port= 21.13in

But when you change the option of slot port from yes to no, the new calculation is exactly 33.13in

Why do they not match for the same thing? Shouldnt a square vent be shorter than a slot port? Did carstereo.com just flip flop them or something? Am I taking crazy pills or what?

As bromo said, the issue is with the difference between physical port length and effective port length.

On the carstereo.com calculator when you mark slot port "yes" the calculator reduces the length of the port by 1/2 of the port width to account for port end correction. If you notice the difference between the two calculators is 12", which is half of 24", which you apparently entered as the port width on the carstereo.com site. The 12volt site does not account for port end correction.

For more on port end correction factor, see here: JL Audio - Car Audio Systems

Without knowing details on the layout of the port in the enclosure, I can't tell you which is accurate. If you are using an enclosure wall as the sidewall of the port, you will need to account for end correction. It would seem odd to have a port that's only 4" tall & 24" wide unless it's horizontal across the bottom of the enclosure. If the port is vertical in the enclosure I would assume the 4" is the width and 24" is the height? Either way, you would only need to subtract 2" from the port length for end correction factor as opposed to the 12" initially calculated (i.e. on the carstereo.com site, put 4" for the width and 24" for the height and mark slot port "yes" if you are using the enclosure wall as a a sidewall for the port).

[bigrank916 72]

So Im designing a new enclosure and have come across a speed bump.

Using the12volt slot port length calculator with these numbers: 24, 4, 6.13, 32= 33.13in

Using carstereo.com port length calculator with the same numbers for a square slot port= 21.13in

But when you change the option of slot port from yes to no, the new calculation is exactly 33.13in

Why do they not match for the same thing? Shouldnt a square vent be shorter than a slot port? Did carstereo.com just flip flop them or something? Am I taking crazy pills or what?

As bromo said, the issue is with the difference between physical port length and effective port length.

On the carstereo.com calculator when you mark slot port "yes" the calculator reduces the length of the port by 1/2 of the port width to account for port end correction. If you notice the difference between the two calculators is 12", which is half of 24", which you apparently entered as the port width on the carstereo.com site. The 12volt site does not account for port end correction.

For more on port end correction factor, see here: JL Audio - Car Audio Systems

Without knowing details on the layout of the port in the enclosure, I can't tell you which is accurate. If you are using an enclosure wall as the sidewall of the port, you will need to account for end correction. It would seem odd to have a port that's only 4" tall & 24" wide unless it's horizontal across the bottom of the enclosure. If the port is vertical in the enclosure I would assume the 4" is the width and 24" is the height? Either way, you would only need to subtract 2" from the port length for end correction factor as opposed to the 12" initially calculated (i.e. on the carstereo.com site, put 4" for the width and 24" for the height and mark slot port "yes" if you are using the enclosure wall as a a sidewall for the port).

Thank you for explaining this to me. I understand now, after you had to lead me by the hand.

One thing though. You say to subtract for end correction. I thought you are supposed to add it?

[bigrank916 72]

If Im using the AJcalc for port length and have multiple ports, do I divide the port length between them? Or is each port to be that length? Im trying to work the formula on my own but the numbers dont seem right. Sure that Im doing it wrong though. Feel like quoting Namath cause Im ssttrruugggglliinngg.

[bigrank916 72]

bumpity bump

[NB50 206]

If Im using the AJcalc for port length and have multiple ports, do I divide the port length between them? Or is each port to be that length? Im trying to work the formula on my own but the numbers dont seem right. Sure that Im doing it wrong though. Feel like quoting Namath cause Im ssttrruugggglliinngg.

Each port should be that length.

[Impious 1,476]

One thing though. You say to subtract for end correction. I thought you are supposed to add it?

The port end correction factor increases the effective length of the port. Therefore, for a given tuning frequency you would need to decrease the physical length of the port by the end correction factor so that the effective length was correct for the tuning frequency.

[Impious 1,476]

If Im using the AJcalc for port length and have multiple ports, do I divide the port length between them? Or is each port to be that length? Im trying to work the formula on my own but the numbers dont seem right. Sure that Im doing it wrong though. Feel like quoting Namath cause Im ssttrruugggglliinngg.

The JL Audio link in my prior post explains the proper way to calculate port length when using multiple ports. I don't have time right now to mess around with that calculator to be able to tell you how to interpret the information it's giving you.

[bigrank916 72]

If Im using the AJcalc for port length and have multiple ports, do I divide the port length between them? Or is each port to be that length? Im trying to work the formula on my own but the numbers dont seem right. Sure that Im doing it wrong though. Feel like quoting Namath cause Im ssttrruugggglliinngg.

Each port should be that length.

Thank you sir.

[bigrank916 72]

One thing though. You say to subtract for end correction. I thought you are supposed to add it?

The port end correction factor increases the effective length of the port. Therefore, for a given tuning frequency you would need to decrease the physical length of the port by the end correction factor so that the effective length was correct for the tuning frequency.

If Im using the AJcalc for port length and have multiple ports, do I divide the port length between them? Or is each port to be that length? Im trying to work the formula on my own but the numbers dont seem right. Sure that Im doing it wrong though. Feel like quoting Namath cause Im ssttrruugggglliinngg.

The JL Audio link in my prior post explains the proper way to calculate port length when using multiple ports. I don't have time right now to mess around with that calculator to be able to tell you how to interpret the information it's giving you.

Thank you very much impious. I knew the answer was right in front of my face but I was just jumbled in the brain thinking about it so much.

It looks bad, I know.