Focal sub installed

[Bwcad1]

You Gain efficency with the 4in port.

if you go with a standard slot make it about 40sq inches.

[Bwcad1]

Not thread jacking here, just wondering on port volume. Port volume will have an effect on frequencies outputted through the port.

But is this one of those things where there is diminishing returns? Continue making the port bigger and you hit a max output through the port? Or does output continue to increase as you increase port volume?

/jack

When you refer to port volume are you saying the amount of air in the physical port could modify the frequency's exiting it? and each woofer is diffrent each box is diffrent but there is a point where to much port will hurt you or make no difference at all.

[tomcat]

And a round port is easier to build.

As you comand I shall build.

Now if I was smart I would have waited to carpet my box....

[Ryan from Ohio]

Smaller ports = more velocity.

[solacedagony]

When you refer to port volume are you saying the amount of air in the physical port could modify the frequency's exiting it? and each woofer is diffrent each box is diffrent but there is a point where to much port will hurt you or make no difference at all.

So there is an "optimal" port volume where too high and too low will both negatively effect output through the port.

[Bwcad1]

So there is an "optimal" port volume where too high and too low will both negatively effect output through the port.

i guess i'm getting confused on the port volume or port area?

[Jonathan]

So there is an "optimal" port volume where too high and too low will both negatively effect output through the port.

Not really. It just gets to a point that the bigger you go, the sheer size of the port and box is impractical.

The port itself performs as a solid mass of air, rather than a hole in a box. The air is effectively trapped within the port walls, and while it doesn't have excursion limits, air flow velocity can negatively affect both output and sound quality. You can model this in WinISD and view the port air velocity in different configurations.

The lower you tune or the larger your box, generally the more port area you need because of the velocity created by the two. I don't really go by a set formula for port area in terms of square inches of port area per the box volume, but rather the velocity created around tuning. Remember that at tuning, the port is really doing most of the work, it's "cracking the whip", sucking energy out of the internal air pressure created in the box, loading the subwoofer because it's using it as the fulcrum to bear the force of it's own acceleration. That's why subwoofer excursion is drastically reduced at tuning. The lower the tune, the more excursion the port is required to have thus the added necessity for port area, just like with subs, you'd rather do it with surface area than with excursion.

The amount of output your subwoofer is capable of will also affect the required port area. Take a 4" port which has roughly 12sq.in of port area. If you have a 12" subwoofer (roughly 100sq.in of area), you've got around an 8-1 ratio of cone to port area. If a 12" sub moved .50", the port would have to move around 4 inches. If the sub moves 1", the port has to move 8 inches etc. Obviously that's a lot of velocity and airflow required by a port.

[geolemon]

I used to be a Focal dealer, and the designs are a little more "old school" conservative. They aren't high excursion subs by any means, nor do they have particularly strong motors. The construction is high quality, the materials are as fine as they use in their midrange drivers, and when they are used as SQ subs, they are outstanding. But they simply aren't SPL subs - they are very much "the subs" you would think of at the extreme SQ end of the spectrum.

[Tim]

they are very much "the subs" you would think of at the extreme SQ end of the spectrum.


that was the way I thought of Focal, also.

Tim

[Ryan from Ohio]

Geo!

Hes alive!

Nice to see ya.