Port area per cube question??

[MrSkippyJ]

Gotcha. So when does the enclosure volume start effecting the port area? I guess that is what I am asking. I see port area per cube often and have wondered how the enclosure volume is related to port area.

[fecupe2001]

In my opinion, it only takes a big effect when it comes to bandwith or the greatest output you are looking for, for example, a big ass port on a small box would have a higher peak than using a big ass box and same big ass port, other than those 2 things, i honestly don´t think i´ve found any relation of box size depending on the port size

[audiofanaticz]

You can go by how much port area you need a couple ways.

The typical way is going off that 12-15sq inches of port per cubic foot of box volume which most do.

While this works its not always the best, but for the average user its more then fine.

The more advanced way and I guess you could say proper way is going off of the woofers surface area, its xmax and xmex, the rms rating of the woofer, and the actual power that will be giving to the woofer. These are things programs like Torres and the RE box calculators do not take into consideration one bit and makes it even a larger juggling act.

Say you build a 8 cubed box after displacement, you use the above first method and do 15sq inches of port per cube (120 sq inches of port).

Now lets say you put a 12in alpine type r in this box and you give it 500 watts rms (half its rated rms power).

This box will most likely sound some what decent on this little power. The enclosure will be VERY efficient in terms of output to wattage and have a rather low impedance rise compared to the woofer being in a box built to spec.

But now you bought yourself a new amp because your woofer is 1000wrms, so you hook up your 1000wrms amp and the woofer starts to sound like complete udder trash.

Your trying to thing why when its a brand new high quality amp and you even hooked up your old amp and it was fine again.

More then likely that woofer with its rated power is having the cone flap around like a fish out of water due to the box not only being way too large, but having way to much port area.

The woofer is acting similar to how it would when its being played with no box (free air).

At this point power compression is coming into play, and no matter how much power you keep adding to the woofer its not getting louder or sound any better but worse.

This is the main reason Im highly not in favor of a lot of these so called box designers.

They know how to use google sketchup really good and make a cool looking box, but the performance is highly questionable with their basic methods behind designing enclosure.

Some of these guys have only built a couple boxes and theres gaps between the panels to big enough to finger.

[audiofanaticz]

Also want to add that bandpass enclosures prove everything I said about ports correct.

It may look great on paper, but the actual performance may not be what it should.

It will take a lot of testing and tuning, making your loading wall/port thicker, thinner, bigger, smaller, and so on.

Fecupes build log shows just that with all the trial and error he went through to get it where he wants it.

[Omega5002]

It's not about how much port you have per cube, it's about total port area. Total port area is actually independant from volume. What Brian said was a very good and helpful explanation.

Its one in the same really, as your port area gets larger so does the port area per cubed.

While port area maybe independent from volume, the actual port length, height, and width effects the box volume and must be included when subtracting displacements from your box just like you would with bracing, subwoo0000000000fers, 45s and so on

Yes, the per cube does appear bigger when you increase the port area, especially if you start out with the same gross volume, but what I mean is that if a subwoofer need 50 sq inches of port for example, then the area should 50 sq inches whether the sub is in a 3 cubic ft net(16.7 per) or 6 cubic ft net box(8.3 per), that's what I mean when I say port area is independent from net volume.

The per cube thing is okay when it comes to beginners, gets their feet wet in designing, but when you start reading more in depth, testing different things, read different theories (like Vance's idea of basing port from sd and xmax) etc, then the per cube figure on a calculator like torres starts becoming an optional figure. I'm not saying I'm an expert on box design, I'm actually I'm still far from it, I'm still learning, and probably won't stop learning.

I also don't agree with most designers you pay online for a design, sure it's okay for a simple throw in the back box, but when it comes to large build, especially the trend of 4th orders I've seen, then it becomes a hit or miss because the cabin or vehicle isn't being tested or being factored, etc.

[Robert8252]

I don't actually know the exact formulas because I haven't messed with them in over a year or two but when it comes to box size and port area Ray who used to be on here told me you are better off getting the most mechanical power out of a speaker over thermal (watts). A bigger box with less power can be just as loud as a smaller box with 3 times the power but you are working the hell out of the motor in the latter and getting a lot of heat = less maintained listening. But its when you find that perfect ratio of mechanical control and power handling you get the best results. A general X amount of net space and X amount of port area generally can create a just fine box that will perform good for the average Joe but when you want the most out of your equipment it takes a lot more then 4 cubes with 15 inches of port tuned to 32. From what I've done personally if your port isn't at least 20 inches long to reach desired tuning frequency there's probably a lot of potential being wasted.

[Kyblack76]

I feel, im leaving a LOT on the table.

Coming down to port area... or maybe box size...

i dunno

[Robert8252]

I feel, im leaving a LOT on the table.

Coming down to port area... or maybe box size...

i dunno

Just needs more cowbell.

[fecupe2001]

Also want to add that bandpass enclosures prove everything I said about ports correct.

It may look great on paper, but the actual performance may not be what it should.

It will take a lot of testing and tuning, making your loading wall/port thicker, thinner, bigger, smaller, and so on.

Fecupes build log shows just that with all the trial and error he went through to get it where he wants it.

it was easy as hell to get it where it is right now,only 7 months lol

And very good works you have spoken on this topic my man, lots of good info!

[CleanSierra]

Good read guys