Port Area Clarification

[MrSkippyJ]

Right on, hopefully its a fun ride, with beer.

and not shitty beer either.

[Triticum Agricolam]

You mean you are moving it slower at lower volume right? Your still moving the same amount of air regardless of volume.

See this is where I have issue. If its all about air speed the port shape is more important than size.

Also if power was that much of a factor then why do pretty much all 12's use about the same size port regardless of power handling?

I understand air speed is a factor and too much causes port noise.

I think it isn't as simple as build based on power.

That's why port area is such a complicated subject and it takes a lot of experience or luck or both to get it right

Ok first off, everything I say here is based on my understanding of how this stuff all works, that knowledge came from my own experience and research. I may very well be wrong.

To answer your first question, no, I do not mean you are moving the same amount of air regardless of box volume. If you have two boxes, one larger than the other, but with the same sub and on the same power you should get a larger volume of air moving through the port of the larger box. This is related to why larger boxes give you more gain around tuning than smaller boxes. I think some people are of the assumption that the air moving through the port is directly related to the air being displaced as the cone moves. This is not the case though. The point where you get the most air moving through the port is right at tuning, which happens to be where the cone moves the least.

A ported box is an air spring and best analogy I got is it is kinda like cracking a whip. A small movement on the handle of the whip results in a larger, much faster movement at the other end. As you make a box larger is like making the whip longer. You get more movement out for what you put into it.

To me port sizing is all about moving air efficiently. This is why I believe both port size and shape are important. Air resistance increases at a square of air velocity. If your air velocities are high, the shape of the port is going to be extremely important as anything that disrupts that flow is going to cause a lot of resistance and work against you. At lower velocities shape is less important since air resistance is soooo much less.

The reason I think power is important to keep in mind is because the port calculations based on Xmax, cone area, and tuning assume you are going to push that sub until it reaches Xmax. This results in a very conservative (large) number. If you built the port to that spec you would be totally fine and I don't think there would be any downside to doing so. However it may be much bigger than what you need and if you don't need to use all the space why should you?

I'm in this to learn as much as I can just like the rest of you, so if anyone thinks I got it wrong, please tell me where and why!!

[Jessica]

i dint say box volume i said volume. You know turn it up to 11?

thats a great write up but it was for the wrong reason sadly

[Triticum Agricolam]

i dint say box volume i said volume. You know turn it up to 11?

thats a great write up but it was for the wrong reason sadly

Lol, my bad. That's what happens when I don't read attentively enough and make assumptions.

Though is this case it doesn't change my answer. You are not moving the same amount of air a different sound volume levels. As you turn the knob up to 11 you have more air moving through that port.

Also same size subs do not use the same size port regardless of power handling. For example, if you look on sundown's site they recommend 28 sq in for the E-12 and 40 sq in for the X-12. That's an increase of almost 50% and if it would me I'd probably give the E-12 less than 28, probably closer to 24 sq in.