# Proximity of ports - air turbulence?



## sapphari (Oct 7, 2013)

I am planning a new build with two 15" subs in a standard ported enclosure, 4cuft/sub. The loaded enclosure will be large and heavy and so I've toyed with the idea of using two separate enclosures. This would make it easier to remove the subs for times that I actually want to use my cargo space (road trips, camping, etc).

The general enclosure design I think would work best for my space is like this:









The rear hatch in my car is curved so the port in the center would give me the most clearance between the port opening and the rear hatch. A port on the left or right side would be ~3" from the hatch and I think that's not enough.

So if I were to split this single enclosure into two, the two ports would be like this, right next to each other. Of course it would be two separate boxes and this is just one, but you get the point.









My question is would the proximity of the two ports create turbulence that would affect output and quality of sound? The drivers are 15" and have 34mm xmax, so at the tuning frequency (32Hz), a lot of air will be moving through the ports. At 16 square inches of port per cubic foot of enclosure, the port velocity models pretty high with 4kW/sub, around 50m/s if I remember correctly.

Is this a terrible idea? Should I just keep as a single enclosure and deal with the inconvenience when it comes up? I suspect it will only be a few times a year I'd have to remove it and put it back in.


----------



## geolemon (Aug 15, 2005)

Not at all a terrible idea.
Both ports will be in phase with each other, so they won't cause any harm to the sound, or interfere with each other. It'll be fine.

Sent from my LM-G710 using Tapatalk


----------



## sapphari (Oct 7, 2013)

Cool, thanks for your input. I also noticed Alpine is doing something similar where they are selling modular loaded enclosures that can be linked together. You buy one, and can add a second later if (let's be honest, when) you want more bass.





__





S-SB12V 12" Alpine Halo Subwoofer with ProLink™


Single 12" Alpine Halo S-Series Preloaded Subwoofer Enclosure with ProLink™




www.alpine-usa.com





The annoying thing for me, is I would have to build two enclosures, which would just take more time.


----------



## Theslaking (Oct 8, 2013)

I had a very similar box for two 12's however you do need to separate the ports at the back wall where they meet. That triangle isn't going to stop them from smashing in to each other and messing up the airflow.


----------



## sapphari (Oct 7, 2013)

Do you have a drawing or photo of how you think it should be done?


----------



## Smitty (Oct 17, 2019)

sapphari said:


> Do you have a drawing or photo of how you think it should be done?


You don't have to worry about that. Since you are building two separate enclosures, the issue he describes will not be present.


----------



## geolemon (Aug 15, 2005)

Theslaking said:


> I had a very similar box for two 12's however you do need to separate the ports at the back wall where they meet. That triangle isn't going to stop them from smashing in to each other and messing up the airflow.


That won't hurt -

As long as the width of the vent in that center section is twice the width of each vent leading out of the separate chambers, it'll function exactly the same as if you had a dividing wall running down the middle - except your box can then be one dividing wall narrower. 😉

You don't even need that triangle back there, technically.

If you were sending separate signals to the two subs, that would be different of course - in that case, any moment just one sub was playing, it would see an effectively larger cross-section port and would technically be tuned higher at that moment - so don't do this unless you are running a mono sub amp.

But even then - even if you ran the two subs off a 2 channel amp, 99% of recordings have the sub-bass encoded in mono at any rate. No big deal.

Sent from my LM-G710 using Tapatalk


----------



## geolemon (Aug 15, 2005)

Smitty said:


> You don't have to worry about that. Since you are building two separate enclosures, the issue he describes will not be present.


Yes - I just wanted to spell it out for other readers.
Good place to learn, these forums. 

Sent from my LM-G710 using Tapatalk


----------



## sapphari (Oct 7, 2013)

I'm not necessarily building two boxes - I may opt for a single enclosure. The purpose of the thread is to get input on what people think about having two ports next to each other - will it cause turbulence that will effect output and sound quality? My inclination is that it is not ideal, and I'm leaning to a single enclosure.

Good point geo - this would be mono signal.


----------



## geolemon (Aug 15, 2005)

It literally won't make a difference any way:
One box, shared center port.
One box, two parallel center exit ports (dividing wall).
Two mirror image boxes, two center-aligned ports.
Two mirror image boxes, ports on the outsides.
Two identical boxes (one port center, one side).

You'll still have exactly the same tuning and no difference in sound quality or noise.

I'd advocate building the mirror image boxes, since
a) it allows you to load/unload the boxes easier.
b) it allows you two orientation options - center port vs side ports.

Then you can also see for yourself. 

Sent from my LM-G710 using Tapatalk


----------

