Help!!! Box !!!

[timb2169 10+ year member]

HELP!!! I dont know how to design a ported box. I know some things but not all....I tried using the tutorial from realm of excursion and i ended up with -6.98 cubes?

My dimensions are

20H x 35W x 32D

looking for 90 sq. in of port area tuned to 30Hz

can someone help me learn how to design a ported enclousre????//content.invisioncic.com/y282845/emoticons/mad.gif.c18f003ab0ef8a0d9c27ca78d77a6392.gif

Click to read more...

 

[Chevillac 5,000+ posts]

Try usign a calculator or contacting one of the box builders on here. I heard Moe Lester does them. Gauntlet, Jmac (i think still) off the top of my head.

 

[tRiGgEr 5,000+ posts]

Length x Width x Height = Cubic inches / 1728 = Cubic feet.

Example - 35L x 32W x 20H = 18902.38 / 10.94ft^3

(subtract building material off of the external dimensions to get the internal dimensions. Here we used .75" MDF so 1.5" off of each dimension to gain internal measurements.)

Now a simple slot port on the side. 18.5H x 5W x 17.5L = 1781.78 / 1728 = 1.03

(add .75" on the width for the building material of the port, subtract .75" from the length due to the part of the box already accounted for in the box displacement.)

That leaves you with 9.91ft^3, 92.5 square inches of port area, and tuned to 30hz.

Now this does not account for speaker displacement, or bracing displacement. You would have to adjust the port's length when you know all of the displacement in the box you will be using (driver, bracing).

Use this as a quick port guide. I find it to be extremely accurate. Just don't rely on the vent diameter section.

http://www.carstereo.com/help2/Articles.cfm?id=31

 

[timb2169 10+ year member]

Well.... WinISD is telling me my port lenght should be about 14 or so inches if tuned to 32Hz...thats what i decided to do instead of 30Hz ....I know that that calcualtion is not with port displacement...i need to know my NET box volume after all displacement for my XXX 18. Total I have 10.939 cubes to work with internal dimensions.

My AVALIABLE dimensions are:

20H x 35W x 32D

Total is 10.939 Cubes

On WinISD I put a port 6 x 18.5. A total of 92 Sq. In of Port Area....However how do you caluculate this all in to teh box volume to get the total box volume net? I have use many calculators, but none incluse port displacement....

 

[timb2169 10+ year member]

Length x Width x Height = Cubic inches / 1728 = Cubic feet.
Example - 35L x 32W x 20H = 18902.38 / 10.94ft^3

(subtract building material off of the external dimensions to get the internal dimensions. Here we used .75" MDF so 1.5" off of each dimension to gain internal measurements.)

Now a simple slot port on the side. 18.5H x 5W x 17.5L = 1781.78 / 1728 = 1.03

(add .75" on the width for the building material of the port, subtract .75" from the length due to the part of the box already accounted for in the box displacement.)

That leaves you with 9.91ft^3, 92.5 square inches of port area, and tuned to 30hz.

Now this does not account for speaker displacement, or bracing displacement. You would have to adjust the port's length when you know all of the displacement in the box you will be using (driver, bracing).

Use this as a quick port guide. I find it to be extremely accurate. Just don't rely on the vent diameter section.

http://www.carstereo.com/help2/Articles.cfm?id=31

Where did u find that lenght from??? (the one i bolded)

 

[tRiGgEr 5,000+ posts]

Well.... WinISD is telling me my port lenght should be about 14 or so inches if tuned to 32Hz...thats what i decided to do instead of 30Hz ....I know that that calcualtion is not with port displacement...i need to know my NET box volume after all displacement for my XXX 18. Total I have 10.939 cubes to work with internal dimensions.
My AVALIABLE dimensions are:

20H x 35W x 32D

Total is 10.939 Cubes

On WinISD I put a port 6 x 18.5. A total of 92 Sq. In of Port Area....However how do you caluculate this all in to teh box volume to get the total box volume net? I have use many calculators, but none incluse port displacement....

If you read my post it tells you exactly how to figure it all out in a simple easy to understand way.

6 x 18.5 = 111 sq inches of port area //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

the sub displaces .25ft^3. If you use no bracing good luck with that.

And WINisd requires you to know basic box building skills. It is just a tool to aid you in the process.

 

[tRiGgEr 5,000+ posts]

Where did u find that lenght from??? (the one i bolded)

I did not find it. I calculated it. After the ports displacment, that is the length required to achieve a tunning of 30hz...

 

[timb2169 10+ year member]

So let me understand this.....

I'm figuering this out right now...

I have 20H x 35W x 32D

great...

Now my next step is to Find my internal dimensions....18.5 x 33.5 x 30.5

Total Box volume for that is 10.939. Now I must tkae my desired port dimensions, which i have decided 18.5 x 5 should be plenty. Total port area is 92.5 sq.in..

What I know: Total cubes so far 10.939. Port Dimensions 18.5 x 5. Port Area: 92.5 sq in.

Next....I am supposed to add .75'' to the port width, and then subtract .75'' from the lenght.

I try on the calculator to find lenght of teh port, and I get 5 inches....This is where i am stuck...is finding the port lenght...

 

[tRiGgEr 5,000+ posts]

So let me understand this.....
I'm figuering this out right now...

I have 20H x 35W x 32D

great...

Now my next step is to Find my internal dimensions....18.5 x 33.5 x 30.5

Total Box volume for that is 10.939. Now I must tkae my desired port dimensions, which i have decided 18.5 x 5 should be plenty. Total port area is 92.5 sq.in..

What I know: Total cubes so far 10.939. Port Dimensions 18.5 x 5. Port Area: 92.5 sq in.

Next....I am supposed to add .75'' to the port width, and then subtract .75'' from the lenght.

I try on the calculator to find lenght of teh port, and I get 5 inches....This is where i am stuck...is finding the port lenght...

Good that is all correct. This is where you use the link I supplied.

http://www.carstereo.com/help2/Articles.cfm?id=31

Scroll to the bottom. Normally I guesstimate the required length. This time I figured 18.5" so I add up the port displacment 18.5 x 5.75 x 17.75 = 1888.16 / 1728 = 1.09.

So 10.94 - 1.09 = 9.85 enter that in to eclosure volume. 30hz as tunning and the port dimmensions.

As you can see it gives a port length of 17.68 so we need to adjust the port length again untill we reach the correct length.

Next I use 17.5 as the length. So 18.5 x 5.75 x 16.75 = 1781.78 / 1728 = 1.03

So 10.94 - 1.03 = 9.91 enter the new box volume.

As you can see it's right on the money with 17.5 for the length with a tunning of 30hz.

Crude and might take a bit longer but it is the best way for me.

 

[I want SExxx 10+ year member]

Well here's how I do it......

Start with you deminsions 20x32x35

Now that's external so the internal deminsions are 18.5x30.5x33.5 which gives us 18902.375 and we need to devide that number (cubic inches) by 1728, which is one square foot. Now we have 10.9388 cubic feet. Well round to 10.94.

Next you gotta take away the sub displacement, which is around .24 cuft. Now were left with 10.70 cubic feet. Now its Time for the port. I'd do a 6" wide port for a total of 111 sqin of port area.

Now here's where it gets tricky. You have no way to get the tuning frequency until you have the net cuft of the box. You don't know how many net cuft. you have the port length. So you gotta do some guestimating and modifying numbers until everything gets right.

So well start out by saying the port will displace 1.7 cuft. and say were going to have 9 NET cuft. The port would then need to be 27.25" long. So 27.25*6.75*18.5/1728=1.96 So I was a little bit off. With this it will be tuned to 30.44 hz, which is close enough for me So I would build to these specs. Up or down one cycle won't audibly change the response of the driver so one being .44 cycles off were good.

8.74 CuFt. NET to 30.44hz

You could however go down to 7 cuft. if needed for the xxx18........ That's a big box for the trunk of a Cutlass.

 

[tRiGgEr 5,000+ posts]

Umm same way I do it...

 

[Moe Lester 10+ year member]

umm, why dont you just figure the airspace you want, then figure out your port displacement, add the driver disp. port disp. and internal net airspace, and then adjust your dimensions to achive the correct airspace

 

[tRiGgEr 5,000+ posts]

umm, why dont you just figure the airspace you want, then figure out your port displacement, add the driver disp. port disp. and internal net airspace, and then adjust your dimensions to achive the correct airspace

Cuz when I find what dimmensions I want to use I stick to them. Then adjust the port to make it fit on the box size I want. I don't use max dimmensions for my box. I use the only dimmensions

 

[gHOstFaCe 10+ year member]

This is what I could come up with. I just drew it up using your given measurements and it gives you 92.5sq" on port area.

 

[timb2169 10+ year member]

Well...thre seems to be an issue now with my intial box dsign. Fact is, it will fit in my car....downside is that there is no way to get it in unless i build it in the trunk....Thats NOT going to happen...

Well...We are going to have to slant the front board. Itstead of doing 20'' High we will slant to a height of 17''. Total Dimensions now are

17'' H x 30''D x 35 W