Port area for 15" BTL

[ckaiser1688 0]

Just picked up a 15" BTL fully loaded ect. How much port area should i have? I've heard 16" per cube but just thought i'd get an exact answer. My box is 3.9 cu. ft.

[thor02 2]

Anywhere from 12-16 is good, depending on your desired tuning. Less port area=lower tuning, with 12" per cube being on the low end.

[ssh 924]

just a good rule of thumb, 12-16 square inches per cubic foot. I personally always like to be on the bigger side so you don't end up with any port noise (chuffing sound)

[ckaiser1688 0]

Alright thanks guys, figured it was around there cause that's how i've always built boxes but just thought i'd double check. Thanks!

[emh9009 199]

Remember, you can't come here and ask a question and not post a build log!

Just kidding... But seriously..

[95Honda 486]

In all honesty, the "port area per cubic foot" rule of thumb is not only meaningless, but just dumb.

If you really want to know the answer to your specific question, you need to model your driver and get a predicted vent velocity with your chosen port. Someone on here may even do it for you if you ask.

Additionally, the minimum vent area is going to also depend on how much power you will have on tap.

Want an easy answer? Don't try and use much less than the the area of a 6" I.D. round port if you are going to use any signifigant amount of power. That is what I would reccomend as a minimum with that driver...

[NDMstang65 403]

In all honesty, the "port area per cubic foot" rule of thumb is not only meaningless, but just dumb.

Works fine..

It's better then trying to show somebody how to model something in an anechoic environment that it will never be in

[onebadmonte 235]

In all honesty, the "port area per cubic foot" rule of thumb is not only meaningless, but just dumb.

If you really want to know the answer to your specific question, you need to model your driver and get a predicted vent velocity with your chosen port. Someone on here may even do it for you if you ask.

Additionally, the minimum vent area is going to also depend on how much power you will have on tap.

Want an easy answer? Don't try and use much less than the the area of a 6" I.D. round port if you are going to use any signifigant amount of power. That is what I would reccomend as a minimum with that driver...

So what modeling software do you recommend? Any tips or how to's, to go along with that?

[ssh 924]

In all honesty, the "port area per cubic foot" rule of thumb is not only meaningless, but just dumb.

If you really want to know the answer to your specific question, you need to model your driver and get a predicted vent velocity with your chosen port. Someone on here may even do it for you if you ask.

Additionally, the minimum vent area is going to also depend on how much power you will have on tap.

Want an easy answer? Don't try and use much less than the the area of a 6" I.D. round port if you are going to use any signifigant amount of power. That is what I would reccomend as a minimum with that driver...

So what modeling software do you recommend? Any tips or how to's, to go along with that?

I know a quite a bit of people use WinISD, not sure if it will work in this application tho.

[95Honda 486]

In all honesty, the "port area per cubic foot" rule of thumb is not only meaningless, but just dumb.

Works fine..

It's better then trying to show somebody how to model something in an anechoic environment that it will never be in

I only think that works if you don't have any amplifier clipping.... lol...

[95Honda 486]

I know a quite a bit of people use WinISD, not sure if it will work in this application tho.

Oh god, I know this must be some "magical" situation wich no software can predict...

[NDMstang65 403]

I know a quite a bit of people use WinISD, not sure if it will work in this application tho.

Oh god, I know this must be some "magical" situation wich no software can predict...

Go ahead and put a BTL in a box that winisd predicts (it is about the size of a shoe box) will have the "flattest" response curve. It does not deal with a very low vas and low qts woofer very well at all as far as 'predicting' an 'ideal' enclosure.

It will be anemic as hell, no bottom end..and peak like a high school prom date. Even though winisd says it should be fairly flat.

The guidelines have worked fine for years, thousands of people have used it. It is MUCH better then spending 12 hours on a phone trying to tell somebody how to model and plot something. You seem to forget that many people who buy these things do not know the difference between a dual 1ohm or dual 2ohm coil or how to wire it. You also seem to forget that the 16 year old kid doesn't "normalize" his amplifier power when he clips the piss out of it either..he just clips the piss out of it.

Not quite sure what has chapped your hind parts lately..but if you don't like it, don't read it. You are only going to confuse them even more by doing so, which causes us even more of a pain in the ribs having to explain why you are confusing the hell out of them.

Please stop.

There is absolutely no need to complicate things more then what they are already. Basic rules of thumb and box designs work absolutely fine and there are no issues with them.

[95Honda 486]

Wtf was that all about?

Sorry if you thought I was coming off like a dick Nick, I wasn't trying to at all man.

My point was many of these "rules of thumb" are just wrong. And just like "How many Dbs" and "That woofer needs 4K watts to even work" get perpetuated into things that are just plain wrong and held as the gospel.

I also never intended to have someone model an enclosure alignment, I suggested they look at vent velocity in thier chose alignemnt, which is the proper way to tackle that problem. You can do that easily with a program like WINisd...

I guess I look at it this way, if they just want a rule of thumb answer, they should just be driected to the manufacturer's website and offered no additional help on this forum. It hey want help beyond that, I am going to give what I believe to be the correct answer.

Again, I wasn't trying to be a dick.

The clipping comment was a joke, BTW....

Edited February 10, 2011 by 95Honda

[Aaron Clinton 2,372]

Mike, I can see both perspectives. From the enthusiast perspective that wants to really hit on the finer details, finding vent velocity is a great idea to make the best of the enclosure. But from a brand stand point, in many cases it is just adding complication and in many cases, customers can get confused. So much of the time it is best to just provide enclosure designs.

[RAM_Designs 25]

Mike, I can see both perspectives. From the enthusiast perspective that wants to really hit on the finer details, finding vent velocity is a great idea to make the best of the enclosure. But from a brand stand point, in many cases it is just adding complication and in many cases, customers can get confused. So much of the time it is best to just provide enclosure designs.

I thought you guys had suggested port area specs as well, like how IA did/does? If not, I think that'd be something good to have; a solid figure(or suggested span) for how much port area is necessary to avoid port noise at full xmax(maybe even more).

Edited February 10, 2011 by RAM_Designs

[NDMstang65 403]

Mike, I can see both perspectives. From the enthusiast perspective that wants to really hit on the finer details, finding vent velocity is a great idea to make the best of the enclosure. But from a brand stand point, in many cases it is just adding complication and in many cases, customers can get confused. So much of the time it is best to just provide enclosure designs.

I thought you guys had suggested port area specs as well, like how IA did/does? If not, I think that'd be something good to have; a solid figure(or suggested span) for how much port area is necessary to avoid port noise at full xmax(maybe even more).

We do..

Basic math..

3-5 cubic feet (you pick 4 cubic feet)

12-16 square inches of port per cubic foot of volume (you pick 14)

14 x 4 = 56 square inches of vent..

Doesn't get any simpler then that.

[NDMstang65 403]

My point was many of these "rules of thumb" are just wrong.

We here at FI CAR AUDIO have used this rule of thumb with great success and so have dozens of clients around the world.

So, we say feel free to use the rule of thumb.

[ckaiser1688 0]

Remember, you can't come here and ask a question and not post a build log!

Just kidding... But seriously..

Haha don't worry. It is currently -7 degrees out so once it warms up ill get a build log on here