Jump to content
Second Skin Audio

WinISD - What exactly is the "Air Velocity" graph?


Recommended Posts

So I've been trying to design some boxes in WinISD. I've looked around on the forums, not sure if i'm just not searching properly or if there's just little info about it. What exactly is the air velocity graph for and how do you read it?

Link to comment
Share on other sites

The smaller the port area, the higher the air velocity will be, the more noise the port will make. Too large an area and you need an absurdly long port. Rule of thumbs(or is it rules of thumb?) I've heard are don't make a port with a dimension less than 1.5" and keep the vent velocity below 20 meters/second. Some people are ok with as much as 30 if the sub is tucked away. 

It's important to input a reasonable wattage in the signal tab. I've heard half RMS is a good starting point.

I went years without knowing what this was just by making ports what seemed to be the "right size."  

Link to comment
Share on other sites

23 hours ago, Robin Dobbie said:

The smaller the port area, the higher the air velocity will be, the more noise the port will make. Too large an area and you need an absurdly long port. Rule of thumbs(or is it rules of thumb?) I've heard are don't make a port with a dimension less than 1.5" and keep the vent velocity below 20 meters/second. Some people are ok with as much as 30 if the sub is tucked away. 

It's important to input a reasonable wattage in the signal tab. I've heard half RMS is a good starting point.

I went years without knowing what this was just by making ports what seemed to be the "right size."  

But what is "Air Velocity" itself? I know what numbers to keep it around but don't fully understand it. I want to know what the graph actually means instead of just winging it.

Link to comment
Share on other sites

Air velocity means air speed. It's an estimation of how fast the air might be traveling inside the port. In meters per second. At a given frequency/signal level.

wEoDI7M.jpg

In this image, you can see I've clicked on the peak of the green line. At 25.46 hz, at the power I've chosen in the signal tab, WinISD estimates that the air in the ports could reach speeds of 24 m/s(meters per second). If 25hz is above my high-pass filter, and if the subs are going to be where I'll be able to hear port chuffing, I may want to:

* enlarge the ports

* add an additional port 

* make the port(s) as round as possible(triangles and squares work, too)

Slot ports work really well for some designs, but they have the highest perimeter area for a given port size. It's the air traveling over the surface of the port/bends that causes audible chuffing.

 

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Who's Online   0 Members, 0 Anonymous, 375 Guests (See full list)

    • There are no registered users currently online
×
×
  • Create New...