Am trying to figure out the port area for round ports in my design. Am going to build an enclosure that is 4 cu.ft. after all displacement turned to 30Hz for a 15" Fi Q. I know that for a slot port, that its length X width to calculate port area (i.e 14 X 4 = 56 sq.in. of port). I also know that for a round port, that its Phi X radius sq. to calculate port area (i.e 3.142X4 for a 4" pipe = 12.568 sq.in of port). This is what am not understanding is, to get the needed port area for using 4" port in a 4 cu.ft. enclosure, you would need about 4 or 5 of them, or am i just full speed down the wrong side of the track? I was going to use a slot port but decided that it would eat up to much room in my cab. So can someone share some advice on what would be the best route to take. Thanks in advance for the input.

Well i would wait for someone else to make sure im right but i think that where your messing up is your not factoring in the length of the port. Heres a Box calc for round port. Speaker Enclosure Volume Calculator

Im not sure why you think you need four or five ports that large for one 15"Q.

A 4ft3 enclosure with a 4" port should be about 6.5" long to achieve a tuning of 30hz.

Am trying to figure out the port area for round ports in my design. Am going to build an enclosure that is 4 cu.ft. after all displacement turned to 30Hz for a 15" Fi Q. I know that for a slot port, that its length X width to calculate port area (i.e 14 X 4 = 56 sq.in. of port). I also know that for a round port, that its Phi X radius sq. to calculate port area (i.e 3.142X4 for a 4" pipe = 12.568 sq.in of port).

Not sure why this is confusing.

Imagine your 14" long port that is 4" tall. By default even without the rounding you can line up 3 4" round ports and fit them in the port. You'd still have 2" left over and all the corners. Easy to imagine that indeed it will take 4-5 to equal the same port area. Perhaps a discussion over how you chose what port area and why you'd even think about using 4" pipe when a 6" would be a lot better would be a good discussion.

Im not sure why you think you need four or five ports that large for one 15"Q.

A 4ft3 enclosure with a 4" port should be about 6.5" long to achieve a tuning of 30hz.

I understand that I would still get the tuning i want with a single port, but what about the port area (Fi recommend 12-16 sq.in per cu.ft. which would be 48-64 sq.ft)? One 4" port would only be 12.568 sq.ft. for a 4 cu.ft. box, wouldn't I have less output with one 4" port than with 2 or 3? Or am I not getting the concept?

Not getting the concept. You cannot run just one 4" port, didn't you read my response?

Not getting the concept. You cannot run just one 4" port, didn't you read my response?

I read your response but still didnt get the concept. Can you explain futher for me, or send me a link that will put me on the right track. Thanks

Fi recommend 12-16 sq.in per cu.ft. which would be 48-64 sq.ft

You have to keep the total area in mind

Let's do the math backwards:

64 / Pi = 20.37

SQRT (20.37) = 4.5" radius or 9" diameter, considering there is no 9" you could do a flared 8" without a problem and just have a single port.

If you have to use wimpy 4" ers then we need to figure out their area. 2*2*Pi = 12.56cuft * 4 = 50.26 (*5 = 62.8). So you'd need 4 to 5 of them.

Now you see why most people slot port their box.

I have no link, but you could look in any Geometry book.

*make sure you use all 4 ports when you calculate your length if you go that route.

Ok I get it. Thanks

m5 did it differently then i would have but he is right. see slot port are easier to fit then 4 round so most will go slot they got the same sound quality or spl if you do it right. btw here is a formula on building boxes and why round port are so hard to fit. they also have a lot of technical under support at this link under woofer box wizard. there is a set of boxes on the bottom right of that page that contain more info on building boxes.

Answer

...I have no link, but you could look in any Geometry book...

That's going in my sig