Port Size

[All_Logix 10+ year member]

About to head into the construction of my first box, have a feeling its going to be a try this try that until I get what I want, but I did have a question about port effectiveness. I have done some calculations, and I want to use slot port because its easier and I don't want to be to ambitious, but from all my options the best one I have come across is a volume of 1.5 ft^3 with a port about 9.5" long, and 13.5" high...but to get it down to 32 Hz, it will only be about 1/2" wide... will having such a slim port effect the port output? Since the sealed recommendation is on .75 ft^3 I don't want the box to be to similar to sealed bit with way to much volume...

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[Audiohazzard 10+ year member]

Go to google and type in re audio box calculator, it will help you out. Good luck man

 

[Kangaroux 5,000+ posts]

Go to google and type in re audio box calculator, it will help you out. Good luck man

Please don't use this one...the RE calculator is terribly inaccurate.

Go here: Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Use the calculator at the bottom of the page to calculate port length. The initial port area should be anywheres between: Net Box Size (in cubic ft) * 12 OR Net Box Size (in cubic ft) * 16.

If the port is too slim it may affect your tuning but most importantly it will cause port noise (air velocity becomes too high).

Port width to port height ratio should be at a minimum of 1:8. I prefer 1:6

 

[Audiohazzard 10+ year member]

It's more accurate than some give it credit for. Type in the parameters of the enclosure and just try them out, hasn't done me wrong yet lol.

 

[Kangaroux 5,000+ posts]

It's more accurate than some give it credit for. Type in the parameters of the enclosure and just try them out, hasn't done me wrong yet lol.

It's right like half the time...if you boot up winisd or any other online calc you'll see that some of the stuff in random places is like a couple inches off

 

[All_Logix 10+ year member]

Thanks guys I figured there was more science behind it than I was giving it credit for, another question, if you run dual subs in a ported box, do you base the port size and length on the total volume of the box alone or does having multiple woofers in it change the way you calculate that?

 

[Kangaroux 5,000+ posts]

Thanks guys I figured there was more science behind it than I was giving it credit for, another question, if you run dual subs in a ported box, do you base the port size and length on the total volume of the box alone or does having multiple woofers in it change the way you calculate that?

Port size and length is based solely on box size. It's when you start adding multiple ports that stuff changes

 

[Buck 5,000+ posts]

Hit me up for a box design!

 

[All_Logix 10+ year member]

Thanks Buck, and normaly I would hand it over to you, but I want to attempt it on my own, I wan't to get better at box building and design... So I redid everything and what do you guys think about a 10.5" tall 2" wide port?

 

[Kangaroux 5,000+ posts]

Thanks Buck, and normaly I would hand it over to you, but I want to attempt it on my own, I wan't to get better at box building and design... So I redid everything and what do you guys think about a 10.5" tall 2" wide port?

for a 1.5 ft^3 that would be ideal.

 

[thevic24 5,000+ posts]

Here is the port cac. that I use. It has always been on par with winsid and others.

It also takes end correction factor into its calculations.

slot port caculator

 

[thevic24 5,000+ posts]

Please don't use this one...the RE calculator is terribly inaccurate.
Go here: Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Use the calculator at the bottom of the page to calculate port length. The initial port area should be anywheres between: Net Box Size (in cubic ft) * 12 OR Net Box Size (in cubic ft) * 16.

If the port is too slim it may affect your tuning but most importantly it will cause port noise (air velocity becomes too high).

Port width to port height ratio should be at a minimum of 1:8. I prefer 1:6

How come when you switch the width and height measurements up it changes the port length? I thought port area is port area and that would not matter?

Example,

A 2cuft box with 26" of port area would need to be around 17.7" long to tune to 40hz. It shouldnt matter if the port is 13" wide by 2" tall or the other way around....

 

[Kangaroux 5,000+ posts]

How come when you switch the width and height measurements up it changes the port length? I thought port area is port area and that would not matter?Example,

A 2cuft box with 26" of port area would need to be around 17.7" long to tune to 40hz. It shouldnt matter if the port is 13" wide by 2" tall or the other way around....

Did you select yes or the slot port? That makes it mess up sometimes..

 

[thevic24 5,000+ posts]

Did you select yes or the slot port? That makes it mess up sometimes..

AH HA!!!

I see what I did there now. Dam Iam the Polish one and I just confused the port calculator...

Works good that way now...Thanks.

 

[RAM_Designs 5,000+ posts]

AH HA!!!
I see what I did there now. Dam Iam the Polish one and I just confused the port calculator...

Works good that way now...Thanks.

When you select slot port it's assuming end correction, so it's giving you the actual length of the wood needed. Not selecting slot port just gives you the raw length needed; it's assuming you're using a free-standing port that doesn't share a wall with the box in order for end correction to be an issue. This is why the non-slot option is longer using that calc. I just use no-slot, and know how long the actual port length needs to be, and just worry about end correction and such on my own.