how much port area do i need?

[andru]

I'm going to attempt my first ported enclosure and I'm trying to figure out how much port area I need. from my understanding if I have less port area I will have more bandwidth or lower f3 but when I try to model this in winisd it doesn't seem to include this. So how do I figure out how much port area I actually need?

here is some info for my system, I'm using 2 15" psi platform 2 subs powered by 2 crescendo s1500.1 amps. my current box is 8.1 cuft after displacement with a port that is 38.25" X 3" and 24" long winch should be around 35hz. it's a sub up port back in a suv

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the issue I have with my current box is it's loud in the 40hz range but rolls of pretty steep into the 30 hz range.

I would really like to hit with some authority in the low 30s, does anyone have any advice?

[Triticum Agricolam]

The reason WinISD doesn't show the change in bandwidth with smaller port area is because that's not how port area works, its a common misconception.

The goal with port area is to have enough so that you aren't losing a ton of output to port compression from high port velocities. How much you will need depends on the specs of your subs, the size and tuning of the box, and how much input power you are running. You mentioned you are running two PSI Platform 2's, but you didn't say what size, I assume they are 15"s?

Getting more low frequency output depends on what the specs of your current box are, a lower tuning frequency may help, so may more port area. Some subs are going to give more low range output than others, depending on their parameters.

[andru]

sorry they are 15"s

how do I figure out how much port area I need? I currently have 114 in of port area, some people have told me 50% of the total cone area and other have told me 25% of the cone area.

[Triticum Agricolam]

On the amount of power you are running your port area should be fine.

Here are some other things to think about. With a port that's 3" tall but 38.25" wide you have a really high port aspect ratio. Those tend to be a bit inefficient. If you decide to build another box at some point, you might consider changing the port layout to lower the aspect ratio. You have enough port area its probably not costing you much output now, but it is something I'd look to improve upon next time.

Your Platform 2 subs have relatively high QTS. This causes them to peak in output a good bit above tuning, around 43 Hz or so. Tuning lower, like say 28 Hz, will get you more low end output, but at the cost of some peak SPL.

[andru]

can I make up for the spl loss by increasing the box volume?

I am about to make a new box, I could do a vertical slot port i could make the port 19.75" tall from the height of the box I was planning and if I made it 6" wide I would have the same amount of port area that I have now.

[Triticum Agricolam]

You can make up for the peak SPL with larger box size, to some degree. There definitely are diminishing returns though.

A vertical slot port of the dimensions you listed would be much preferable IMHO.

[andru]

thanks

is how large I can make the box dependent on the cone excursion?

the recommended enclosure size from psi is 3.5-5.5 cuft per sub and I am giving them less than rms so could I give them 10 cuft or is that getting into diminishing returns?

[Triticum Agricolam]

With the amount of power you are running, from an excursion standpoint you would be totally fine at 10 cu ft (or 12 cu ft for that matter, but if you have that much space, get some 18"s).

However the difference in output around tuning between an 8 cu ft box and 10 cu ft box is only going to be about 1 db. It would be mostly unnoticeable. Your biggest gains in low frequency output will be from a lower tuning frequency.

[andru]

thanks for helping, guess I have myself a project for next weekend.