Splitting One Port Into Two Smaller Ports?

[PRIVATEpastry 10+ year member]

I'm planning my box for the new PB XS-12D1V.2 I ordered. The Powerbass website says that the port needs to be 4" round and 14" long. Would it be possible to use two 4" round 7" long ports instead of the one 14" long port?

Btw, I searched and couldn't find anything on this topic.

Thanks in advance for the help, guys.

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[Moe Lester 10+ year member]

no, if you increase the area you will have to also increase the port length and enclosure size

 

[PRIVATEpastry 10+ year member]

So... My enclosure is 9" deep, how could I make the ports fit? Any suggestions?

 

[PRIVATEpastry 10+ year member]

Bump.

 

[PRIVATEpastry 10+ year member]

Anyone...?

 

[diatribe 10+ year member]

Curved bends in your port.

 

[PRIVATEpastry 10+ year member]

Hah, that would be smart... //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif Thought I was smarter than that...

Asthetically, though, I think 2 ports would be better, could I split the 14" port that they want into two 7" ports?

 

[squeak9798 5,000+ posts]

http://mobile.jlaudio.com/support_pages.php?page_id=165

Multiple Ports

There are two widely used methods for calculating multiple ports for a single chamber. Only one method is correct but unfortunately it is the least commonly used.

The first and incorrect method takes it's thinking from the original port formula and says basically that if we take two ports and sum their cross-sectional areas, we can just plug this total into the port formula for Av to get our port length. This would sound reasonable, but it can lead to serious mis-tunings in some cases as we'll see in an example below.

The second and correct way to figure out how long each port should be follows this simple three-step procedure:

• Divide the chamber volume by the number of ports you wish to use for that one chamber.
  
• Take the quotient and use that as your Vb (box volume) in the port formula
  
• Do the number crunching and figure out how long each port should be.
  

Example:

Let's take an arbitrary box volume of 2.5 cubic feet that we want to tune to 25 Hz with a 4" diameter port. If we plug and chug with that big hairy formula (or let our favorite software package churn out the numbers), we'll find that Lv = 18.844 inches.

Now let's decide that we don't want just a single port because it looks boring. Let's put a 2" port in each corner of the box for a total of 4 ports and see what the two methods give us:

Method 1:

Each 2" port has a cross-sectional area of 3.142 square inches so we multiply that by 4 to get 12.57 square inches. Plugging in 12.57 for Av in the port formula yields Lv = 18.844 inches for each port.

Method 2:

We want to use 4 ports so we divide 2.5 cubic feet by 4 and get .625 cubic feet. Vb now becomes .625 cubic feet. We are using 2 inch diameter ports so Av is 3.142 square inches. Plugging these numbers into the equation leads to Lv = 20.302 inches for each port.

Notice that Method 1 produces the same port length as did our single 4" diamter port as it should (after all, we have the same total port cross-sectional area which this school of thought proclaims is correct!). But the first method is incorrect because it neglects the frictional losses encountered by using many smaller ports--there is a higher port wall surface area to cross-sectional area ratio which raises the total amount of frictional losses in the ports and thus shifts the tuning!

 

[PRIVATEpastry 10+ year member]

D*mn, I plugged in the numbers into the port formula, just to check and see if it would come out equal, and it said 34hz = 1385.68. Did I do something wrong here? Are Powerbass' enclosure specs messed up?

I'd appreciate it if someone took a look at this and pointed me in the right direction.

Here is the link to the Powerbass XS driver page. I'm using a single XS-12D1V.2 in this box.

 

[squeak9798 5,000+ posts]

Did you remember that the box volume needs to be in cubic inches for the formula and not cubic feet?

 

[req 5,000+ posts]

just get some flexible tubing or use bend joints in your PVC

if its a daily driver, im sure the bends wont make that big of a difference.

 

[PRIVATEpastry 10+ year member]

Did you remember that the box volume needs to be in cubic inches for the formula and not cubic feet?

Uh, no I didn't. Thanks!

just get some flexible tubing or use bend joints in your PVC
if its a daily driver, im sure the bends wont make that big of a difference.

Asthetically, though, I think 2 ports would be better, could I split the 14" port that they want into two 7" ports?