can someone explain how port velocity works

[Jessica]

I was going to say.

I thought area was determined by power.

[ChevyBoy95]

I was going to say.

I thought area was determined by power.

Amount of air that can be displaced by the cones I thought.

Power can dictate it though, because at 100% power in theory 100% xmax, you will have 100% displacement, at 50% power, you might only have 60% displacement, etc.

[Jessica]

I was going to say.

I thought area was determined by power.

Amount of air that can be displaced by the cones I thought.

Power can dictate it though, because at 100% power in theory 100% xmax, you will have 100% displacement, at 50% power, you might only have 60% displacement, etc.

yes, cone area plays a part. But if you have 4 250 watt 12's, or 4 5k 12's the port area will change vastly.

[hdorre]

yes, cone area plays a part. But if you have 4 250 watt 12's, or 4 5k 12's the port area will change vastly.

yes, volumetric displacement has an immense affect on port velocity.

power is an additional factor as well, like you previously stated.

[DLHgn]

So many wrong things were said in this thread. That in^2 to ft^3 rule of thumb is not accurate at all. Krakin, Chevy, Strange and hdorre for sure know what they're talking about. Sorry BMS but you must have been misinformed at some point.

[akuma4u]

ok i need some confirmation - in the attached pic, the area circled red, that value should be under 10 in order to prevent port noise.. is this correct? also - whats the difference between port compression vs port velocity? if the % of mach is under 10 is that all i need to worry about?

[Joe X]

0.10 may take care of noise but you may still have compression, you want to be like 0.05 or below for an efficient port, specially slot ports where you have sharp edges and turns.

[akuma4u]

So the 5 i have in red circle is the same as 0.05 Correct?

[Jessica]

Maybe i dont understand, but from what i have seen and read, port noise is just a thing you will have in a car if you are running any kind of mid to high end drivers. You simply dont have the room in most vehicles to get proper port area.

I Think most people would never even hear port noise over what the subs are doing and most your noise is going to happen right at tuning where your port is doing all the work anyway.

But i could be wrong, its happened before.

[Joe X]

So the 5 i have in red circle is the same as 0.05 Correct?

W is acoustical power not electrical power so that result is invalid, that said those formulas are not as reliable as modeling curves, some 35-37 square inches of port area would be good enough for the 40Hz you want.