Box calculations, any help would be appreciated

[filtor1 13]

So here is what I came up with.

40"L x 18"W x 16"H using 3/4" MDF. Gross internal cf is 5.33cf.

I figured around .18cf displacement /driver (estimated) and will be left with 4.97cf

I bought 2 4" Precision Ports. There calculator on thier site recommends a Straigh Length of 9.48" and Flare length of 10.48" to achieve a tune of 32Hz in a 5.33cf box. I can handle that length with what was provided in the kit from Precision Ports.

Here is where I get messed up. Being left with 4.97cf before taking out port displacement, I can't seem to calculate the volume in cf that these ports will take up. I have tried several different calculators and will continue to try and figure this out. This is where I ask for help.

This box will be housing 2 12" AA Havocs and will be powered by a SAZ3000D. Is this box ok for these subs? It fits withing the parameters of the AA recommended size, but is there some consideration I need to make concerning the power I have on tap and the box size relative to the drivers capabilities. Or am I analyzing this too much.

Thanks in advance, Chris

[BKOLFO4 29]

It is close enough to just estimate the displacement as a 4" port. I use 14 in^2 * length to get volume displacement of each port.

Also - the volume used to calculate the length for a given tuning frequency is based on the net volume, not the gross.

Determine what volume you want to use, find the port length. Add the volume + port displacement + driver displacement to get gross volume. Adjust your dimensions to get that gross volume.

Brian

[filtor1 13]

So I should do 4.97cf less the approximation of the port displacement and do the port length to get roughly 4.57cf to determine the length of the ports?

I also should mention I am attempting to keep the box dimensions within the stated parameters due to not wanting to build the box in the trunk. So that is the biggest I can go. Thus the reason I am working through the problem the way I am.

Edited January 20, 2009 by Chris

[filtor1 13]

I just recalculated the port length at 4.57cf and it 11.55" and 12.55" respectively.

[mccleery3 166]

I'm trying to figure out disp. for 4-4" psp ports with a length of 14.61" each in a 8 cube net box, any help is greatly appreciated. Sorry for the slight thread jacking, but why start another for such a similar question?

[filtor1 13]

I'm trying to figure out disp. for 4-4" psp ports with a length of 14.61" each in a 8 cube net box, any help is greatly appreciated. Sorry for the slight thread jacking, but why start another for such a similar question?

Doesn't bother me at all. The experienced people can kill two birds with one stone.

[mccleery3 166]

Right on bro! That's why I only registered to this forum and left ca alone.

[rushnrun 14]

pi x radius^2 x Heigth

if a 4" port

3.14 x 2^2 x Port length

that'll give you cubic inches then divide by 1728 to get cubic feet

**don't worry so much about the flares just treat it like your average cylinder.. the flared portion won't take up enough space to make any real difference

[filtor1 13]

OK, 3.14x2^2x12.55= 157.628/1728=.09122

If I am correct, that means .09122x2= .1824cf is the displacement of both 4" aeros each having a length of 12.55"

So in reality, 4.97cf-.1824cf= 4.788 cf. So /2 and I will net 2.394cf per driver. All of these calculations fall within the recommended specs too.

Does this look correct to you guys.

And thank you to BKOLF04 and rushnrun for your assistance.

[filtor1 13]

If I am correct chicagofan, your aeros would be 3.14x2^2x14.61= 183.502/1728= .106x4=.425cf for all 4-4" aero ports at 14.61" in length.

[rushnrun 14]

OK, 3.14x2^2x12.55= 157.628/1728=.09122

If I am correct, that means .09122x2= .1824cf is the displacement of both 4" aeros each having a length of 12.55"

So in reality, 4.97cf-.1824cf= 4.788 cf. So /2 and I will net 2.394cf per driver. All of these calculations fall within the recommended specs too.

Does this look correct to you guys.

And thank you to BKOLF04 and rushnrun for your assistance.

looks close enough....

IMO you really DON'T have enough port area.. you really need about 2 of th areos per sub. however the length you would need wouldn't work out..

Edit:left out a word Don't makes a big difference in that statement

Edited January 20, 2009 by rushnrun

[filtor1 13]

OK, 3.14x2^2x12.55= 157.628/1728=.09122

If I am correct, that means .09122x2= .1824cf is the displacement of both 4" aeros each having a length of 12.55"

So in reality, 4.97cf-.1824cf= 4.788 cf. So /2 and I will net 2.394cf per driver. All of these calculations fall within the recommended specs too.

Does this look correct to you guys.

And thank you to BKOLF04 and rushnrun for your assistance.

looks close enough....

IMO you really DON'T have enough port area.. you really need about 2 of th areos per sub. however the length you would need wouldn't work out..

Edit:left out a word Don't makes a big difference in that statement

How do I know what would be enough port area? Is there a spec that can be used to calculate or know how much is required? The last box I had utilized a 4"Wx14"Hx17"L slot port in a smaller enclosure but I didn't design or build it. How much port area would you suggest? Would it be better to sell the 4" aero's and revert back to a slot port? I could do 4-4" aeros and port through the rear deck, but I am trying to keep it as simple as I can for now.

[rushnrun 14]

well you use to have 56in^2 of port (the old box was probably just about right) and you'll now have only 25in^2 if using 2 areos... the flares help with the port noise but.... I ran an SE 12 on 2 4" areos and it still had port noise (I was running it off of 3000+watts at the time)

the larger the box the more area you need.... 12-14 in^2 of port per cubic foot is suppose to be ideal (I don't use this method but everyone on here seems to post it) so by that you'd need 60-70in^2 of port which is more than twice of what you will have with the two areos...

Slot ports are nice because you can get more area for the same length/tuning, however you also have to tak into account of the increased port displacement which increases the port lenght...

***I never use areos for my boxes for three reasons...

1. Personal preference_they're easier to tune for my application

2. Cost_you can buy a whole sheet of MDF for the cost of 1 areo port

3. Shorter vent lenght/surface area

*****I don't have anything against them I just don't use them anymore....

[filtor1 13]

well you use to have 56in^2 of port (the old box was probably just about right) and you'll now have only 25in^2 if using 2 areos... the flares help with the port noise but.... I ran an SE 12 on 2 4" areos and it still had port noise (I was running it off of 3000+watts at the time)

the larger the box the more area you need.... 12-14 in^2 of port per cubic foot is suppose to be ideal (I don't use this method but everyone on here seems to post it) so by that you'd need 60-70in^2 of port which is more than twice of what you will have with the two areos...

Slot ports are nice because you can get more area for the same length/tuning, however you also have to tak into account of the increased port displacement which increases the port lenght...

***I never use areos for my boxes for three reasons...

1. Personal preference_they're easier to tune for my application

2. Cost_you can buy a whole sheet of MDF for the cost of 1 areo port

3. Shorter vent lenght/surface area

*****I don't have anything against them I just don't use them anymore....

I see. I will give them a try, since I have 2 sheets of 3/4" mdf and see which I like better. I will build one box with the slot port and another with the aero's. The good thing about this install this time around is I have decided to try some new things. So if the first one doesn't work, then I will throw the slot ported one in. I can always scrap the other.

I appreciate your input.

[BKOLFO4 29]

The great 12" challenge used (1) 4" aero with a single sub and had no problems.

There are multiple claims that say you can get away with 1/2 the normal port area with an aero.

Let us know what you think when you get the box built. . .

[filtor1 13]

The great 12" challenge used (1) 4" aero with a single sub and had no problems.

There are multiple claims that say you can get away with 1/2 the normal port area with an aero.

Let us know what you think when you get the box built. . .

I have also read those same threads. That is actually why I chose to try the Precision Ports. I have known others to have great reviews, so who knows. I shall test.

[mccleery3 166]

I appreciate you doing my math too Chris. I came up with the same numbers so I owe BKLOFO4 and rushnrun a big thank you as well.

[filtor1 13]

I appreciate you doing my math too Chris. I came up with the same numbers so I owe BKLOFO4 and rushnrun a big thank you as well.

Any time!

[filtor1 13]

I had a free day today and decided to start laying out my panels. I have also decided to go ahead with the slot port. I want to avoid any chuffing, especially because the subs and port are firing directly into the cabin this time.

I have use a couple of different online port length calculators and some of them are giving me conflicting information.

The box is 40" X 16" X 18". I want to try and build the port in the center for weight balance issues and to add strength to the box. The port is going to be 4" wide and 14.5" tall (internal dimensions. The net volume I get is 4.12cf, and 5.33 gross.

One calculator I used gave me a port length of 30.76". http://www.the12volt.com/caraudio/boxcalcs.asp#rec

Another gave me a port length of 28.67". http://www.mobileinformationlabs.com/HowTo...20lenth%201.htm This is with the slotted port option selected. Without it I get the 30.76" as in the previous calculator.

Which one of these sources should I go with?

I would love to get this done today if at all possible. I wonder if I am being to picky over two inches of port length.

Chris

Edited February 10, 2009 by Chris

[filtor1 13]

Also, when doing a center port, do I split the difference between the two rear panels? Or do I make them both equal to the total length independently. My center part of the port is 14.75" after taking into consideration the back wall .75 and the width of 4". The total length, if it is indeed 31", would I take 31"-14.75"-.75" for the width of the walls so = 17". Do I need to add a 14.5' X 17" piece to each side to achieve the required port length? I am still using a 32Hz tune.

I hope someone understand what I mean. I don't really know how to explain it better.

Edited February 10, 2009 by Chris

[filtor1 13]

Here is a few more places I tried to calculate the length.

28.76" http://www.carstereo.com/help/Articles.cfm?id=31

RE gave me 13.25". http://www.reaudio.com/speaker_box/LPort_Box_Calc.html

[filtor1 13]

I contacted Fisher Customs to design one for me. I will let you know how it turns out.