Double port question

[speakerdude123 10+ year member]

Was wondering if it is more practical/efficient to have a double port in your box? I'm building a box for an 18" woofer right now and have never really liked the idea of bending the port around the back wall, so it it feasible to cut the port length in half of the original port and make two ports?

For example, if I had a port length of say 30 inches. Could I create a 15 inch port on both ends of the box and achieve the same frequency as the 30 inch port?

If so is there a down side to this or is it less efficient then having just one port? I was thinking with an 18" sub your going to be moving a lot of air and why not make it easier on the sub by having less restriction on the airflow?

Thanks for reading

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[k_schutte 10+ year member]

You have to keep port area in mind as well as port length. A lot of people do dual ports, I prefer aero now days over slot but...

 

[RAM_Designs 5,000+ posts]

Was wondering if it is more practical/efficient to have a double port in your box? I'm building a box for an 18" woofer right now and have never really liked the idea of bending the port around the back wall, so it it feasible to cut the port length in half of the original port and make two ports?
For example, if I had a port length of say 30 inches. Could I create a 15 inch port on both ends of the box and achieve the same frequency as the 30 inch port?

If so is there a down side to this or is it less efficient then having just one port? I was thinking with an 18" sub your going to be moving a lot of air and why not make it easier on the sub by having less restriction on the airflow?

Thanks for reading

Ports don't work like that. Doing two ports that add up to the same port area as a single port will require to two ports each to be slightly longer than the single one of equal area. Simply halving port size and length at the same time will greatly raise your tuning. And honestly, a single 90* turn is not a big deal. Throw a 45* piece in the corner to give you the same port width from it to the inside corner of the port, and round-over the inside corner and you'll still have very smooth air flow.

You can also make the inside corner of the port angled as well so you have a pair of 45* turns instead of a single 90* turn.

 

[speakerdude123 10+ year member]

Then can you explain how ports work please? I thought you just needed "x" amount of port area for "x" amount of freq.

Are you saying that it is less efficient, and I shouldn't waste my time with it?

Thanks

 

[T3mpest 10+ year member]

Then can you explain how ports work please? I thought you just needed "x" amount of port area for "x" amount of freq.
Are you saying that it is less efficient, and I shouldn't waste my time with it?

Thanks

No he is saying that just because you halve the area you won't actually halve the amount of length needed. If you have 2 ports they will be acoustically summing and nearly acting as one port. If your port is supposed to be 4" wide and 35" deep if you want to do it as 2 2" ports you'll still need probably 30ish inches to keep the overall tuning the same. 2 2" ports with only 17.5 each would be ALOT higher than that single 4. If port cross sectional area remains similar your going to need very similar length overall, you can't cheat it lol.

The disadvantage of dual ports is that yes, it is less acoustically effecient. You'll have reduced port noise this way though vs a single port of larger size though. Somtimes if your very close on your port noise and can't fit the extra length using 2 ports is a good compromise.

 

[speakerdude123 10+ year member]

Okay, I guess that would make sense