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View Full Version : Figuring Sq-inches of port per cube



bgowdy31
02-05-2014, 12:25 AM
This may be sorta confusing lol....

Ok so generally speaking when figuring the amount of port per cube, what is taken into account for aeroports(<IM USING AEROPORTS). I know that for aeros ive read 7-9 sq inches per cube and ive seen people say 9-12 sq inches as well. Then i see it depends on power, or sub etc. Then you have people say to use more port with smaller boxes and less port with bigger ones etc.

In my build im using aeros either 2-8s or 1-12".... i know that they roughly equal the same amount of square inches, tho the 1-12 has a couple more square inches then 8's. I also know that less ports are more efficient.

Heres what im looking at in my system if anyone wants to give their input:

-- 2 Obsidian V2 18's
-- 2 8" aeros(100.48 sq-inches) VS 1 12" aero(113.04 sq-inches)
-- 3kw
-- 10 cubes net after all displace

My goal is most SPL output, but NOT on burps, i play music.

What are your opinions for the amount of inches per cube of port using aeros would you think,
and please dont insist on other options, my only item in question is the aeroports to go 2-8s or 1-12?

bbeljefe
02-05-2014, 01:31 AM
Port area and volume aren't related. At least, not to any appreciable degree. Port area has a direct relationship to tuning and xmax.

Thus, if you have too little port area it isn't because your box is too small or large, it's because at the tuning you chose, your sub moves more air than the port can pass. Likewise, if your sub doesn't move much air and you have a huge port, it's subject to unload... regardless of box volume.

In answer to your question about which port to use, I'd have to know xmax and tuning to say.

bgowdy31
02-05-2014, 02:47 AM
Port area and volume aren't related. At least, not to any appreciable degree. Port area has a direct relationship to tuning and xmax.

Thus, if you have too little port area it isn't because your box is too small or large, it's because at the tuning you chose, your sub moves more air than the port can pass. Likewise, if your sub doesn't move much air and you have a huge port, it's subject to unload... regardless of box volume.

In answer to your question about which port to use, I'd have to know xmax and tuning to say.


ok im tuning my enclosure to 38 hz because i dont listen to really low stuff usually nothing below 34hz honestly.

so tuning will be 38hz & sub xmax is 20mm

bbeljefe
02-05-2014, 10:13 AM
ok im tuning my enclosure to 38 hz because i dont listen to really low stuff usually nothing below 34hz honestly.

so tuning will be 38hz & sub xmax is 20mm

I wouldn't tune those subs that high in that small an enclosure, unless I was shooting for a burp box. They're low EBP subs (really low) and small enclosures will make them peak higher than tuning to begin with. Not to mention, higher tuning needs more port area. That's why OA recommends such low tuning and if it were me, I'd tune them at 25Hz. Even there, they will still have a peak at ~40Hz but they'll also have some decent low end response.

But anyway, I modeled these subs in WinISD Beta and you're good with either two 8" or one 12" port at 38Hz and below. Obviously, the 12" port would be more efficient.

bgowdy31
02-05-2014, 04:14 PM
I wouldn't tune those subs that high in that small an enclosure, unless I was shooting for a burp box. They're low EBP subs (really low) and small enclosures will make them peak higher than tuning to begin with. Not to mention, higher tuning needs more port area. That's why OA recommends such low tuning and if it were me, I'd tune them at 25Hz. Even there, they will still have a peak at ~40Hz but they'll also have some decent low end response.

But anyway, I modeled these subs in WinISD Beta and you're good with either two 8" or one 12" port at 38Hz and below. Obviously, the 12" port would be more efficient.

my blazer it self peak is at 50hz tho. And i dont like tuning super low because i want it to be able to still meter pretty well, and i know its harder to get higher numbers at lower freqs. So idk if i want to tune to 25hz.

again i dont listen to a alot of stuff under like 34hz, if i tuned to 34hz were would potentially peak at?

bbeljefe
02-05-2014, 04:19 PM
my blazer it self peak is at 50hz tho. And i dont like tuning super low because i want it to be able to still meter pretty well, and i know its harder to get higher numbers at lower freqs. So idk if i want to tune to 25hz.

again i dont listen to a alot of stuff under like 34hz, if i tuned to 34hz were would potentially peak at?

You'd be be okay at 34 as far as SPL but the low end extension is gonna fall more steeply as you raise tuning... unless you have another 2-4ftⁿ to give each sub.

bgowdy31
02-05-2014, 04:42 PM
You'd be be okay at 34 as far as SPL but the low end extension is gonna fall more steeply as you raise tuning... unless you have another 2-4ftⁿ to give each sub.

yea im at my max with the 10 cubes lol, unless i did subs and port firing up, but that just seems to difficult to design. But again with the low end i dont listen to really low stuff anyway. for example the lowest song i may listen to is probably "Walk with a waddle by gorilla zoe" and thats like 35hz at the lowest note.

bbeljefe
02-05-2014, 04:58 PM
yea im at my max with the 10 cubes lol, unless i did subs and port firing up, but that just seems to difficult to design. But again with the low end i dont listen to really low stuff anyway. for example the lowest song i may listen to is probably "Walk with a waddle by gorilla zoe" and thats like 35hz at the lowest note.

Well, lets face it... with two 18s it isn't like you're not gonna be able to play anything low, lol. So with that said, I think you'll be fine with 34 but I seriously wouldn't tune higher because with the box volume you have your peak is gonna happen on the high side of the tuning frequency.

bgowdy31
02-05-2014, 05:11 PM
Well, lets face it... with two 18s it isn't like you're not gonna be able to play anything low, lol. So with that said, I think you'll be fine with 34 but I seriously wouldn't tune higher because with the box volume you have your peak is gonna happen on the high side of the tuning frequency.

i see so tune it around 34hz then, i just dont want the bass to be punchy. so in your opinion do you think i should go with 2 8s or 1 12"? im gonn be making them myself so...

Buck
02-05-2014, 05:38 PM
Port area and volume aren't related. At least, not to any appreciable degree. Port area has a direct relationship to tuning and xmax.

Thus, if you have too little port area it isn't because your box is too small or large, it's because at the tuning you chose, your sub moves more air than the port can pass. Likewise, if your sub doesn't move much air and you have a huge port, it's subject to unload... regardless of box volume.

In answer to your question about which port to use, I'd have to know xmax and tuning to say.

Port area and volume are related because if you increase the size of an enclosure with the same woofer, the port will need to get larger in order to keep the same vent speed.

Now to get the port area to use in the first place, depends on box size, power levels, port tuning, and a lot more woofer parameters than just Xmax like Fs, BL, Vas, Sd.

Buck
02-05-2014, 05:43 PM
And almost every woofer in car audio will work somewhere within a port area of say 10-17 in^2 of port area for cube for regular ported. Even though it's dependent on individual vent speeds for one single box to determine size, they usually fall within that range of 10-17. So I don't see how port area per cube is completely irrelevant.

bgowdy31
02-05-2014, 05:49 PM
Port area and volume are related because if you increase the size of an enclosure with the same woofer, the port will need to get larger in order to keep the same vent speed.

Now to get the port area to use in the first place, depends on box size, power levels, port tuning, and a lot more woofer parameters than just Xmax like Fs, BL, Vas, Sd.

ughhhhhh lol...... you know what im going to keep it simple. Is 10 - 11 sq-inches per cube enough for this enclosure...

Buck
02-05-2014, 06:07 PM
ughhhhhh lol...... you know what im going to keep it simple. Is 10 - 11 sq-inches per cube enough for this enclosure...

I think I'd do the 2 8's here.

bgowdy31
02-05-2014, 06:29 PM
I think I'd do the 2 8's here.

ok that will do. now just have to build the enclosure and will put the 2 8s along the bottom/middle of the box side by side and see how it goes. so should i tune by what he was saying to tune lower or go with my original tune of 38hz

Buck
02-05-2014, 11:14 PM
ok that will do. now just have to build the enclosure and will put the 2 8s along the bottom/middle of the box side by side and see how it goes. so should i tune by what he was saying to tune lower or go with my original tune of 38hz

Tune wherever you want. If you aren't going to play lows and you just want it as loud as possible, just tune it where you usually do. You know what you like.

bbeljefe
02-05-2014, 11:53 PM
I didn't say volume is completely irrelevant. But the more relevant thing for a DIY box builder to look at is xmax and tuning when designing a box, for a variety of reasons. The most important in my opinion, being that enough port area for one car audio sub can be entirely too little for another car audio sub in the same box volume with the same tuning. And vice versa.

This is why so many people have problems with their boxes... because they start with a low xmax sub in a prefab with enough port area for that sub and then, when they go larger their bass doesn't sound right and they bash the prefab when in reality, it isn't the fault of the box. And to boot, the same thing could happen to you or I if we build a box for an entry level sub and the buyer winds up shoving a high powered sub in it later on.

And 10-17inē per cube is a wide range, especially when one considers that most people build 3-4 cube boxes for 15s. What you're saying in that scenario is than any car audio 15" sub should be fine with anywhere from 40-68inē of port area and that's simply not true.