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#### Silas

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I'm somewhat new to ported subs, but I understand the basics. However, what is the absolute maximum port air velocity that can be used without tons of port noise? I am designing two subs, one extends much lower than the other but has much higher port velocity (65m/s). The other doesn't extend as far (but still pretty low!) but only has about 30m/s of port velocity.

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I try to stay around 25m/s maximum. But that being said some bigger ports 6"+ with big round over entry and exits can be useful up past 35m/s. Lots of variables.

#### fusseli

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It depends on the size of the port. They say that 17 m/s is the general limit, but I think that's more for 3" round ports. Higher is okay for bigger ports, and even lower than 17m/s for smaller ports. 60m/s is wayyyyy too high.

#### gperkins_1973

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I'd say there are so many variables in a design which accounts for low and high velocity. What driver was you modelling etc.....

#### ach81090

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The velocity in and of itself is not the problem. The problem is when the flow goes from laminar to turbulent, and the turbulence is enough to produce audible distortion. You could try to predict the type of flow by calculating the Reynolds number.

I remember finding a port calculator from some Australian site that helped you figure out the smallest possible port to use but I can't remember the name. It's on the tip of my tongue, I'll post it up when I remember.

Here's a link to a Reynolds number calc: EDIT not enough posts to put a URL. google engineering toolbox.

#### ach81090

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I just remembered, it's called "flare-it".

You definitely should be using a flared port. Make sure it's flared out both sides not just the front. Remember, the air mass is oscillating, so both sides function as an inlet, as well as an outlet.

I recommend to use the dimpled port ends(IIRC, dimples in the main part of the port don't make a significant difference) from madisound, that way if you do end up with a some turbulence the dimples will create a boundary layer for better flow. If none of that makes sense think of why a golf ball looks the way it does.

And I am assuming you are not able to go with a larger diameter port, otherwise you probably would have just done that.

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