The Port Area Thread

[numatik]

And that is still minimum vent not optimum. So really quite pointless, called trial and error there bud. LOL

There is also one other little thing people often overlook called the vehicle it is going in, take the same exact enclosure put it in an SUV, a car, and an extended cab pickup, one or two of those vehicles the sub will likely unload under certain conditions, ei windows up down, door open closed, direction of sub and port. Again Trial and error is your friend.

i have done lots of trial and error, i was just looking for a forumla, like how you tune an enclosure. your right that says minimum, but also dosnt say what too much vent is. I dunno its an interesting topic that i havnt done much reading on here, seems to be like a grey area in car audio you know? you have some interesting points too

[Torres]

The size of the enclosure has nothing to do with how much port area you'll need. It's dependent on how much air the sub itself is going to displace and the frequency at which you'll be tuning. The same sub moving the same amount in two different sized boxes will not need two different sized ports to "avoid port noise."

i see people touch on this point a lot, but never go in depth with it. mind explaining in more detail what specs to look for and how to get it correctly? i have a basic knowledge of it but none i quite feel safe with trying to give an in depth description of. there's enough people jumping the gun and posting information they think is right when it's not

[numatik]

The size of the enclosure has nothing to do with how much port area you'll need. It's dependent on how much air the sub itself is going to displace and the frequency at which you'll be tuning. The same sub moving the same amount in two different sized boxes will not need two different sized ports to "avoid port noise."

i see people touch on this point a lot, but never go in depth with it. mind explaining in more detail what specs to look for and how to get it correctly? i have a basic knowledge of it but none i quite feel safe with trying to give an in depth description of. there's enough people jumping the gun and posting information they think is right when it's not

[Ray]

I have a formula..

Involves sd, fs, and power.

Seems to work pretty good across the board.

I know..... Share...

Sorry, I gotta keep this one to my self.

Vent has a lot to do with rise .......bl has a lot to do with rise........the motor has a lot to do wth bl......

Rise at fs has a lot to do with the vol of the enclosure.....

I will share soon, just got one more comp, then I will share it.

[7jezuz7]

I used this and so far in my two ported boxes I've done for one DC level 3 12" and then 2, I was not disappointed with the results in my car, an 01 Impala.

The formula is to calculate amount of air displacement (in box) by the subwoofer(s) and then implement that into the port to maintain linearity between box volume air displacement and port volume air displacement.

a constant ---> 39.37[tuning freq. * [xmax * sd(our cone area)])^.5 to find port area, just using a few subwoofer parameters. the xmax by cone area is to calculate displacement. Then what I do is look at the required volume as per the manufacturer's website. And in my case 1.5^3 per sub was recommended but I went with 1.75^3 as I'd be under powering them by a bit. What I do then is use Torres' calculator to input my sub volume and leave that amount fixed then I go and add external port until I get to my desired tuning frequency as per the formula and then once I've found dimensions, I go back and change my dimensions to add the port into the total measurement.

Okay, so going to the DC Audio website, I find that the cone area for one sub is 494 cm^2 but for the formula it's needed to use meters or so I was told. So converting that it would then be .0494m^2 for my cone area but I'm using two so .0988m^2 now we have that and we multiply by xmax which is 22.5mm or .0225m and multiply by whatever tuning we want then raise to the ^.5 power. in my case I chose around the 32hz area and finally the constant in the formula and you should get a number which would be your port diameter and you change as necessary for a slot port.

So here we go:

Port diameter = 39.37 * [ 32(hz) * (.0225m(xmax) * .0988m^2(cone area))]^.5

= 39.37 * [32 * .002223]^.5

= 39.37 * [.071136]^.5

= 39.37 * .266713...

= 10.5005 in. the diameter

Now change to port area into slot form

Diameter = 10.5005 then Radius = 5.25025

Now for area pi*r^2 = pi*(5.25025)^2 = 86.5984 in. and that's the minimun port area to use for my subs and of course your numbers don't have to be exact because there are so many variables in car audio so using say a port of 7"x 12.625" = 88.375 in. is perfectly fine. I chose to tune to 32.5Hz by the formula so that's why my area is a bit bigger.

And a few vids if you want, underpowered in each case with only about 450-500 watts rms each.

One sub esp. @ 2:00 in the vid :

Both subs:

[tigolbity]

I say make a changable/removable port so that you can mess around with it till it sounds good to you.

knowing what EXACTLY to tune it to is pointless, there are a lot of other variables that will effect the tuning.

[Torres]

I have a formula..

Involves sd, fs, and power.

Seems to work pretty good across the board.

I know..... Share...

Sorry, I gotta keep this one to my self.

Vent has a lot to do with rise .......bl has a lot to do with rise........the motor has a lot to do wth bl......

Rise at fs has a lot to do with the vol of the enclosure.....

I will share soon, just got one more comp, then I will share it.

now this...is something i am going to scour the forum for. when is this last comp?

[Torres]

I say make a changable/removable port so that you can mess around with it till it sounds good to you.

knowing what EXACTLY to tune it to is pointless, there are a lot of other variables that will effect the tuning.

neat idea at first, but the more you change port area/tuning, the more you affect volume. a certain frequency/port area might work best with a given volume which you might not be able to attain without rebuilding the box. it may work to an extent but still takes trial and error.

[RAM_Designs]

i see people touch on this point a lot, but never go in depth with it. mind explaining in more detail what specs to look for and how to get it correctly? i have a basic knowledge of it but none i quite feel safe with trying to give an in depth description of. there's enough people jumping the gun and posting information they think is right when it's not

I can't give any sort of technical explanation. It's just what I've noticed through experience, and it's what makes sense using logical reasoning. I'm pretty sure we both understand why it theoretically should work that way(higher tuning needing more port, assuming same amount of excursion). That being said, there are instances where you wouldn't necessarily want to decrease port area when tuning lower. This is mainly because program material below 35hz or so starts to be more felt than heard, and there's less output coming from the sub itself to cover up the presence of port noise(not to mention the port is going to be working like crazy). Having the box close to you makes this port noise, which would normally be hidden by sheer output(with a higher tuning) or trapped in the trunk, much more noticeable on the lower notes.

[Ji553r]

so then these are just myths as rules of thumb:

smaller ports extend frequency response but isnt as loud.

Larger ports are more peaky, louder "boomier" but allow more unloading below tuning and increase box rise?