Port Area Clarification

[Triticum Agricolam]

I don't understand how power is a factor. I mean if you build a larger port because you have more power how will the box perform at lower volume.

If you are building a box for pure SPL I think it would make sense.

Someone want to explain this?

The more power you use, the higher your port velocities are going to be, all else being equal. Port velocity does not = SPL. SPL comes from volume of air moved. It doesn't matter if you have a volume of air moving through a small area at high speed or the same volume of air moving through a larger area a lower speed, the result is the same. The problem with high port velocities is air resistance increases by a factor of 4 every time air speed doubles. So if you have high port velocities you can be losing output to air resistance.

Lower volumes aren't going to perform any differently than higher volumes, you are just moving less air.

[Cj Kumz]

Wanna clarify something here. Is the Xmax used to calculate port area linear or peak to peak?? I have always used peak to peak I'm I safe?

[MrSkippyJ]

but don't you calculate port area based at least on part by xmax, which would take into consideration the effect power would have anyway?

[gckless]

Xmax, by definition, is one-way travel.

[Jessica]

I don't understand how power is a factor. I mean if you build a larger port because you have more power how will the box perform at lower volume.

If you are building a box for pure SPL I think it would make sense.

Someone want to explain this?

The more power you use, the higher your port velocities are going to be, all else being equal. Port velocity does not = SPL. SPL comes from volume of air moved. It doesn't matter if you have a volume of air moving through a small area at high speed or the same volume of air moving through a larger area a lower speed, the result is the same. The problem with high port velocities is air resistance increases by a factor of 4 every time air speed doubles. So if you have high port velocities you can be losing output to air resistance.

Lower volumes aren't going to perform any differently than higher volumes, you are just moving less air.

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

[Cj Kumz]

Port area is determined by Xmax, cone area and tuning frequency of the box. Mostly power doesn't matter as long as the subwoofer's enclosure can allow the sub to reach its xmax.

[MrSkippyJ]

The amount of movement would change how much air is being moved, and more power would increase the amount of movement. But that being said, xmax is rated at highest power rating, so using that to calculate port area would already take into consideration how much power you are using. Lower amounts of power would just not reach the limits of port area.

If I understand this right anyway, which is a big IF since I don't really understand this stuff

[Jessica]

The amount of movement would change how much air is being moved, and more power would increase the amount of movement. But that being said, xmax is rated at highest power rating, so using that to calculate port area would already take into consideration how much power you are using. Lower amounts of power would just not reach the limits of port area.

If I understand this right anyway, which is a big IF since I don't really understand this stuff

you might move more air outside the box but a normal listening levels more power doesnt move more air in the box. There is only so much air in the box to be moved.

[MrSkippyJ]

Yeah I get that.

I am trying to understand this stuff here, so if I am asking questions that you are already explaining it's just me not understanding something, not trying to argue!

But what I think I understand is that, if a sub is only moving 1mm on low power, there is much less air going through the port. If that same sub moves 25mm on full power there will be more air moving through the port.

Is this right?

I guess I am saying as power increases, the amount a sub is moving increases, therefore increasing how much air is going through the port.

[Jessica]

Yeah I get that.

I am trying to understand this stuff here, so if I am asking questions that you are already explaining it's just me not understanding something, not trying to argue!

But what I think I understand is that, if a sub is only moving 1mm on low power, there is much less air going through the port. If that same sub moves 25mm on full power there will be more air moving through the port.

Is this right?

I guess I am saying as power increases, the amount a sub is moving increases, therefore increasing how much air is going through the port.

I dont fully understand either. I'm just here for the ride. I'm pretty sure there are no or few experts in this thread.