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View Full Version : Aero Vs Slot Ports



arizona
06-03-2008, 09:27 PM
I searched around but can't find an answer.

Would either one displace less if they were tuned to the same frequency. I am just curious because I am really short on space. I have to make the box an awkward shape just to get all I can out of the trunk. I dunno for some reason it just seems to me like the Aero would displace less.

Thanks, Jon

miker
06-03-2008, 11:36 PM
With Aero's you can generally get away with less port area, and it is easy to make them external.

arizona
06-04-2008, 12:00 AM
There isn't going to be any room in the trunk for external ports....so if its inside it doesn't matter?

maldecido33
06-04-2008, 12:03 AM
Areo's are most commonly used because it is easy to take them out and modify the length to change the tuning of your enclosure. Other than that, there really isn't much upside to using them vs. slot ports. Both displace (assuming aero's are flared, which they should be) approximately the same volume. Any difference in displacement is typically neglible.

king ranch
06-04-2008, 12:03 AM
a aero for my box in a 5.2net box and is for 2 12's l7's is aeroported one 6" at 34hz and only takes up .14cuft so it makes a huge difference in amount of airspace not taken up from port
and aeros will be louder some say and less port noise and also with a port u can change the tuning freq

tommyk90
06-04-2008, 12:08 AM
You can usually use less port area if you are using aeroports, which in theory will already displace less air.

Even with that, an aeroport will displace less air than a similarly sized slot port. Aeroports are thin walled PVC while a slot port will be made out of 3/4" wood.

So you save mucho airspace going with aeros. :)

stopdrpnro
06-04-2008, 12:12 AM
unless you do alotta work with a router the aeroports will give you better airflow which mean less port noise and higher spl. another benefit of aeroport is simplicity . aeroports= build a sealed box and slide in the aeroport. slot ports box are more tricky to design. last aeroport will save you alot in weight . that said i'm not going back to slot ports.

maldecido33
06-04-2008, 12:14 AM
You can usually use less port area if you are using aeroports, which in theory will already displace less air.

Even with that, an aeroport will displace less air than a similarly sized slot port. Aeroports are thin walled PVC while a slot port will be made out of 3/4" wood.

So you save mucho airspace going with aeros. :)

I've never actually calculated it, but wouldn't the flare on both ends of the aero come close to matching the displacement added by the wall of MDF? (obviously this becomes neglible when you have multiple bends in the port)

tommyk90
06-04-2008, 12:32 AM
I've never actually calculated it, but wouldn't the flare on both ends of the aero come close to matching the displacement added by the wall of MDF? (obviously this becomes neglible when you have multiple bends in the port)

No.

The flare is nowhere near the same displacement as a piece of MDF.

Flipx99
06-04-2008, 12:33 AM
No.

The flare is nowhere near the same displacement as a piece of MDF.

Indeed.

psp says the flare is actually negligble in calculating displacement.

maldecido33
06-04-2008, 12:37 AM
No.

The flare is nowhere near the same displacement as a piece of MDF.


Indeed.

psp says the flare is actually negligble in calculating displacement.

Autocad confirms :(

I just assumed (visually) it would have some sort of effect. Wierd.

Haunz
06-04-2008, 12:31 PM
The accoustical length of a slot port is longer then a regular port or an aero port. That means for a given tuning frequency with the same amount of port area the slot port will be shorter and take up less volume inside the box.

If you are concearned about the volume the extra slab of wood will take up, use some 1/4" hardwood ply

king ranch
06-04-2008, 12:33 PM
http://www.caraudio.com/forum/showthread.php?t=282921

answers alot of questions you might have

btdickey99
06-04-2008, 12:38 PM
The accoustical length of a slot port is longer then a regular port or an aero port. That means for a given tuning frequency with the same amount of port area the slot port will be shorter and take up less volume inside the box.

If you are concearned about the volume the extra slab of wood will take up, use some 1/4" hardwood ply

I personally wouldnt feel comfortable using this

Haunz
06-04-2008, 04:22 PM
I personally wouldnt feel comfortable using this

with little bit of bracing it would be fine... ;)

tommyk90
06-04-2008, 08:37 PM
with little bit of bracing it would be fine... ;)

bracing=displacement. :)

Pretty much negates any added airspace.

Haunz
06-05-2008, 12:33 PM
^ I don't think 4 3/4" X 3/4" strips of MDF is going to displace much volume :rolleyes:

tommyk90
06-05-2008, 05:08 PM
^ I don't think 4 3/4" X 3/4" strips of MDF is going to displace much volume :rolleyes:

I wouldn't even bother.

Just make it out of 3/4" like it should be.

Do some simple math. Say he does a simple slot port that only requires one piece of wood.

Say that port is 3" tall, 20" wide, and 12" deep (60 sq. in. of port). Port displacement for a 3/4" piece of wood is .49 cubes.

The same port made out of 1/4" ply displaces .42 cubes.

A SINGLE .75" x 4.75" x 11.25" (the length of the port) piece of bracing displaces .02 cubes. And one of those isn't sufficient bracing for such a large port. You would have use at least two. So that brings up the bracing displacement up to .04 cubes. Add that to the 1/4" ply port displacement and it brings it up to .46 cubes.

You would want to put forth all that effort of measuring and cutting bracing (and buying different wood) for .03 cubes?

Gimmie a break. :rolleyes:

Haunz
06-05-2008, 11:28 PM
^^ Math > you ?

I don't know what kind of backwords example you are trying to use... but If you are looking at overall port displacment including the wood.... the total volume taken up by a port with
20"x12"x3" internal dimensions made with a single 3/4" wall that measures 20"x12" is .5208 cubes.... the total volume with the same port with a single 1/4" port wall with four 3/4"x3/4"x12" braces is .4670 cubes......


The point is moot.... no significant difference would be made....


However, the point is that a slot port with equal port area and tuning will displace less volume then a regular round or aero port... even if you use a 3/4" wall....

if you want to debate something lets look at the difference between a 3/4" wall slot port and a typical pvc port if the exit velocity is kept the same....

tommyk90
06-05-2008, 11:49 PM
^^ Math > you ?

I don't know what kind of backwords example you are trying to use... but If you are looking at overall port displacment including the wood.... the total volume taken up by a port with
20"x12"x3" internal dimensions made with a single 3/4" wall that measures 20"x12" is .5208 cubes.... the total volume with the same port with a single 1/4" port wall with four 3/4"x3/4"x12" braces is .4670 cubes......


The point is moot.... no significant difference would be made....


However, the point is that a slot port with equal port area and tuning will displace less volume then a regular round or aero port... even if you use a 3/4" wall....

if you want to debate something lets look at the difference between a 3/4" wall slot port and a typical pvc port if the exit velocity is kept the same....

Sorry, I should have made myself clear. The OVERALL port length is 12", so the port wall itself is only 11.25" long since you have to add on the the depth of the enclosure wall.

But the argument is still there. Really no benefit to wasting your time with 1/4" hard ply to gain less than .1 cube.

And how do you figure a slot port will displace less air? Take two 4" aeroports for example. 25 square inches of port area.

Say we do a 2 cube net enclosure. Port length will have to be 31".

(31x(3.14 x 2^2))/1728=.23 cubes. Multiply that by 2 for two ports and you get .46 cubes.

A similar sized slot port will have dimensions of 2.5 x 10 x 26 to acheive the same tuning frequency. (3.25 x 10 x 25.25)/1728=.475 cubes.

These numbers were made using psp's website (the maker of aeroports) and my box program which is dead on with every box program out there and uses mathematical formulas.

Granted this is just an example, but your statements aren't true in all cases. And on top of that, you can usually get away with less port area using aeros because of the flared ends and increased efficiency, thus making the difference between them even larger, but once again an insignificant amount.

arizona
06-06-2008, 12:24 AM
Thanks for all the replies guys.... Don't know if it matters but I am hoping to get 7-7.5 net for the enclosure. I have been busy with work and school so I haven't had time to figure out the new dimensions on what I want to do in the trunk. So I guess after I get that all final I will just calculate if its worth the extra money etc.

Haunz
06-06-2008, 07:01 PM
But the argument is still there. Really no benefit to wasting your time with 1/4" hard ply to gain less than .1 cube.

It was a suggestion since he is hard up for space.... and every bit of extra space certainly helps...



how do you figure a slot port will displace less air?

Because the end correction "k" is significantly larger for a slot port sharring three walls of an enclosure then it is for a regular port; so the port does not need to be as long...


Take two 4" aeroports for example. 25 square inches of port area.

Say we do a 2 cube net enclosure. Port length will have to be 31".

(31x(3.14 x 2^2))/1728=.23 cubes. Multiply that by 2 for two ports and you get .46 cubes.

A similar sized slot port will have dimensions of 2.5 x 10 x 26 to acheive the same tuning frequency. (3.25 x 10 x 25.25)/1728=.475 cubes.

These numbers were made using psp's website (the maker of aeroports) and my box program which is dead on with every box program out there and uses mathematical formulas.

Granted this is just an example, but your statements aren't true in all cases. And on top of that, you can usually get away with less port area using aeros because of the flared ends and increased efficiency, thus making the difference between them even larger, but once again an insignificant amount.


It's convienient that you factor in the air displaced by the MDF but not the pvc pipe... that stuff is 3/16" thick and as far as I am concearned the 3/4" mdf slot port will still displace less volume... and what may I ask did you use as an end correction value for the slot port ? I doubt you even know...


since you like to do examples go ahead and compare a box with a 2.5"x10" slot port made with 1/4" stock braced with metal brakets and k = 2.2... to a box with two 4" dia regular ports with k=.73 (factoring in 3/16" PVC this time)

Mr Cabinetry
06-06-2008, 08:33 PM
I didn't want to jump in to this discussion because the last few post arguing over port size's and displacement is pretty much a matter of fighting over what amounts to nothing more than a minor difference.

But, to be on point, if the enclosure volume is fixed in terms of net volume only and you calculate aero vs slot:

aero ports are longer, BUT, displace less volume

Slot Ports are shorter, BUT, displace more volume

This is Based on 3.0 cu.ft. tuned @ 35hz - 2 4" dia aero port vs 1 slot port of the same port area.

The aero's ports - 16.5" vs Slot Port - 15.75"

And as far as end correction factor goes, you don't subtract from the length, you add to the length, so in actuality the slot port would be longer in you want to be totally **** about the whole " MATH " business.

One other thing, when you calculate for the length of a slot port, you only account for the part of the port that's displacing the volume within the enclosure, the part of the port beyond the interior is not part of the displacement, not the total length of the port.

You could also split the same hairs over what the actual displacement being accounted for for an aero port as well, though I didn't see anyone bring that part up.

For you learning enjoyment:
http://www.subwoofer-builder.com/port-flares.htm

Scroll down to Effective Length

tommyk90
06-06-2008, 09:43 PM
It's convienient that you factor in the air displaced by the MDF but not the pvc pipe... that stuff is 3/16" thick and as far as I am concearned the 3/4" mdf slot port will still displace less volume... and what may I ask did you use as an end correction value for the slot port ? I doubt you even know...



3/16"? What the hell kind of PVC are you using?

The PVC used in aeroports is less than 1/8" thick, I just went out and measured it. Overall diameter comes out to ~4 1/8".

A slight miscalculation on my part, but a gross overestimate on yours.


I didn't want to jump in to this discussion because the last few post arguing over port size's and displacement is pretty much a matter of fighting over what amounts to nothing more than a minor difference.

But, to be on point, if the enclosure volume is fixed in terms of net volume only and you calculate aero vs slot:

aero ports are longer, BUT, displace less volume

Slot Ports are shorter, BUT, displace more volume

This is Based on 3.0 cu.ft. tuned @ 35hz - 2 4" dia aero port vs 1 slot port of the same port area.

The aero's ports - 16.5" vs Slot Port - 15.75"

And as far as end correction factor goes, you don't subtract from the length, you add to the length, so in actuality the slot port would be longer in you want to be totally **** about the whole " MATH " business.

One other thing, when you calculate for the length of a slot port, you only account for the part of the port that's displacing the volume within the enclosure, the part of the port beyond the interior is not part of the displacement, not the total length of the port.

You could also split the same hairs over what the actual displacement being accounted for for an aero port as well, though I didn't see anyone bring that part up.

For you learning enjoyment:
http://www.subwoofer-builder.com/port-flares.htm

Scroll down to Effective Length

Thanks for the info. I will say, though, that some of the things you stated are the ways I calculate my enclosures (the port displacement inside the box only for example, thus why I said a 12" long port will only have a 11.25" length inside the box).

I don't want to say that you're backing me up, but people would rather hear it from you than me. :)

Haunz
06-06-2008, 10:20 PM
I didn't want to jump in to this discussion because the last few post arguing over port size's and displacement is pretty much a matter of fighting over what amounts to nothing more than a minor difference.

But, to be on point, if the enclosure volume is fixed in terms of net volume only and you calculate aero vs slot:

aero ports are longer, BUT, displace less volume

Slot Ports are shorter, BUT, displace more volume

This is Based on 3.0 cu.ft. tuned @ 35hz - 2 4" dia aero port vs 1 slot port of the same port area.

The aero's ports - 16.5" vs Slot Port - 15.75"

And as far as end correction factor goes, you don't subtract from the length, you add to the length, so in actuality the slot port would be longer in you want to be totally **** about the whole " MATH " business. [/I]


huh ?

it's not rocket science... 16.5 x a given area will always displace more volume then 15.75 x that same area... no more bs 'examples' are needed...

Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)

Dv = port diameter (cm)
Fb = tuning frequency (Hz)
Vb = net volume (litres)
Lv = length of each port (cm)
Np = number of ports
k = end correction

(for a slot port Dv = 2*((W*H)/pi)^0.5)


Clearly, for the same tuning frequency the length of the port DECREASES with an INCREASING end correction factor.... (ie slot port)

tommyk90
06-06-2008, 10:25 PM
huh ?

it's not rocket science... 16.5 x a given area will always displace more volume then 15.75 x that same area... no more bs 'examples' are needed...



How do you come to that conclusion?

If the walls are thinner on the 16.5" length, then it will displace similar (or possibly less) than a thicker wall on a 15.75" length port.

Even with the addition of 1/8" to my calculations, that still brings up the aeroport displacement up to .48 cubes, the same displacement as the slot port.

WHY THE **** ARE WE STILL ARGUING ABOUT THIS?!?! It's completely irrelevant.

Haunz
06-06-2008, 10:31 PM
3/16"? What the hell kind of PVC are you using?

The PVC used in aeroports is less than 1/8" thick, I just went out and measured it. Overall diameter comes out to ~4 1/8".

A slight miscalculation on my part, but a gross overestimate on yours.




alright, you got me... 3/16" is standard for ABS platic which is commonly used for ports and is what I was thinking of... you would have 1/8" thick PVC, which is a whopping 1/16" difference in thickness..


At this point it would seem we are into semanticst, but I will stand by my assertion that a slot port will displace less volume then a regular port, if not at least brace the box...

tommyk90
06-06-2008, 10:35 PM
alright, you got me... 3/16" is standard for ABS platic which is commonly used for ports and is what I was thinking of... you would have 1/8" thick PVC, which is a whopping 1/16" difference in thickness..


At this point it would seem we are into semanticst, but I will stand by my assertion that a slot port will displace less volume then a regular port, if not at least brace the box...



It's actually about 1/16" in thickness, so now we're talking a 1/8" difference. :p:

Haunz
06-06-2008, 10:35 PM
How do you come to that conclusion?

If the walls are thinner on the 16.5" length, then it will displace similar (or possibly less) than a thicker wall on a 15.75" length port.

Even with the addition of 1/8" to my calculations, that still brings up the aeroport displacement up to .48 cubes, the same displacement as the slot port.

WHY THE **** ARE WE STILL ARGUING ABOUT THIS?!?! It's completely irrelevant.

the next box I build is going to use a 1/32" sheet of carbon fiber laminate for the slot port... FTMFW...



humor aside, End Correction Factor is serious business

tommyk90
06-06-2008, 10:37 PM
the next box I build is going to use a 1/32" sheet of carbon fiber laminate for the slot port... FTMFW...



humor aside, End Correction Factor is serious business

Whenever I calculated end correction for an enclosure (using winISD, which I usually hate) it never came out to more than a 1 hz difference in tuning. Completely unnoticeable IMO.

Thus, I never do it.

You have to remember, I'm in the SPL competition world, so tuning on the fly is a must for me. I really like aeroports. :)

Mr. Opportunist
06-06-2008, 10:54 PM
drum roll please.....

and the winner is.....

TommyK!

:p:

Mr Cabinetry
06-07-2008, 12:00 AM
Haunz,

You one of those **** retentive types that like to cruise around forums splitting hairs over mickey mouse bullsh!t that has been hacked, carved and chopped to death.

End Correction Factor ain't serious business, you only make want to appear that way.

If end correction factor is such wonderful thing, then explain how adding to the length of the port is a correction when in fact is does nothing more than change the whole parameter of the enclosure design????

If one variable is changed, then everything changes, the length of the port changes, thus, the volume changes, thus the port tuning changes and in the grand scheme of things for the everyday banger, end correction doesn't mean squat.

I'm with Tommy on this one " It's completely irrelevant. " It's only relevant to you because you got a wild hair up your azz about splitting that same hair and for what, to gain .000 something cubic feet that won't even be noticeable.

Granted, when I design an enclosure, I try to be as spot on as possible, but, I'll be d@mn if monkey diking factions of a 1/32" is going to make an enclosure design sound like azz.

There's no such thing a " prefection " and I suggest you get over it.

Haunz
06-07-2008, 01:05 PM
Mr. cabinetry..... look at the forumla I posted again, it is based on net volume of the box....


End correction factor is serious business.. ask any mechanical engineer... clearly the physics behind this discussion reach far beyond building speaker boxes.... and if end correction was meaningless, then it would not be used to calculate port length to begin with....

This thread had everything to do with what kind of port would be best suited to a box with serious space resistrictions.... As far as I am concearned the right answer is the smallest slot port that will keep maximum port velocity under 20m/s using the thinest reasonable material for the port wall... IMO 1/4" oak or birch ply would be just fine... and I'm sure something even thinner could be found...

At the end of the day if you want to chalk the differences in volume up to being "meaningless" then you might as well go with a pair of slot ports using 3/4" material that will also brace the box.... of course two pages ago statements were made that regular ports would displace less air; and since I've shown that to be incorrect now "it's completely irrelevant" and according to you I have a hair up my ***... :laugh:


BTW, slot ports can easilly be flared.. if you know how to do a series of kerf cuts....

Mr Cabinetry
06-07-2008, 01:34 PM
Again, your arguments are nothing more than exercise in making yourself look so d@mn smug in your single mindedness of trying to be correct regardless of what anyone says of does to disprove your logic.

For you to even accept for moment that could be wrong is unthinkable, god forbid you consider such a thought that your own ego wouldn't be able to tolerate it.

Good Day!!!