Xmax

[vw passat]

hi smd I have a question. if u have a 10mm , 23mm or 36mm of xmax wich one needs more port area per foot ?

thanks smd

[SnowDrifter]

Can't answer.

Port area per foot is a rule of thumb. What you are after is TOTAL port area, which you get from tuning frequency, driver size, and power

[vw passat]

so the xmax is not important for the port area per foot?

[Krakin]

No port area per foot is not important or as important as commonly thought.

Also snow you need the xmax also for determining port area. Power is important but it comes into play for how much power is required to achieve xmax. Box size also goes along the same lines of power. Lets say you have a 12" driver in a 1.5 cube enclosure and the same 12" driver in a 2.5 cube enclosure. The driver in the larger enclosure will achieve xmax with less power than the smaller enclosure.

[SnowDrifter]

Xmax =/= total driver displacement. Suspension and other mechanical limitations have more of an effect on the required port area than just the raw xmax.

Example being a sundown X series sub. Xmax is in the 30mm range, like most other high end drivers. Due to the large surround, it even Hass less cone area than most similarly sized drivers. But yet it is a sub that really needs a lot if port. Not because of xmax, but because of how much air it can displace. Xmech is more effective than xmax when trying to figure out an enclosure IMO

And to OP: If you haven't picked up on this by now, there is no cut and dry answer. Wish I could give it to you but there is none. The port area per cubic foot rule of thumb is because of all this. It's easier for the new folks to wrap their head around. Think of it like an average, not an actual rule to follow. Something so you don't have someone building their first 2 10s box with a single 2" pvx pipe as a port

[Krakin]

Example being a sundown X series sub. Xmax is in the 30mm range, like most other high end drivers. Due to the large surround, it even Hass less cone area than most similarly sized drivers. But yet it is a sub that really needs a lot if port. Not because of xmax, but because of how much air it can displace. Xmech is more effective than xmax when trying to figure out an enclosure IMO

Do you know of an effective way of finding the xmech of a woofer? I would just like to know and I haven't done any searching on that yet. I can see that being much more useful especially from my knowledge Xmax, along with it being mechanically dangerous, the output is measured at 10% distortion.

[bkolfo4]

Also snow you need the xmax also for determining port area. Power is important but it comes into play for how much power is required to achieve xmax. Box size also goes along the same lines of power. Lets say you have a 12" driver in a 1.5 cube enclosure and the same 12" driver in a 2.5 cube enclosure. The driver in the larger enclosure will achieve xmax with less power than the smaller enclosure.

This is why power does not really matter.

Cone area, Xmax, and tuning frequency are the main variables, unless you can actually model the driver in the enclosure to determine it will not reach Xmax based on the enclosure and power applied. But if you limit port area in this case, what happens when you decide to buy more power?

[DylanBunch]

im kinda surprised port per foot isnt as important..... cause isnt it how much port area there is just broken down by how many cubic feet the box is? I feel like if you go buy recommended specs in box size it needs x amount of port area, therefore port per foot having a big role in how it sounds, maybe im just pulling this out my ass?

[bkolfo4]

Port area is based on air velocity. Air velocity is based on volume swept by the sub and the frequency the port is tuned to.

I have used these 2 examples many times:

If 18" A has 6mm of Xmax and will handle 100 watts and 18" B has 30mm of Xmax and handles 4000 watts, they will not REQUIRE the same amount of port area even if the box is the same size (they can have the same amount, it is just not required on the sub that will not be pushing as much air).

Or you can look at it like this - if I put a sub in 4 cuft and power it to Xmax, or I put the same sub in 8 cuft and power it to Xmax, it will require the same amount of port area. No reason for the small box to not need as much port area.

[DylanBunch]

oohhhhhhhhhhhhh ok, that makes a lot of sense