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View Full Version : Designing a ported box with George

IgnoreMe
11-05-2004, 02:25 PM
So i notice some guys here need help designing box. well may i suggest you try and give it a shot yourself first? ill help ya ;)

Step 1: Measure your trunk too see what your max dimensions are. Then subtract twice the thickness of the mdf your gonna use (usually 3/4" so subtract 1.5"). This gives you the internal dimensions you need for the upcoming equations. example, your max dimensions are 10" high and 20" wide so so your internal dimensions will be 10-1.5=8.5" and 20-1.5=18.5".

Step 2: Now remind your self of what internal box volume you need, pick a tuning frequency, and pick a port area.

Step 3: Figure out port length using this formula
Lv = Av*1.84*10^8/[Vb*1728*(Fb/0.159)^2] - 0.823*sqrt(Av)

Lv is port length (what your solving for)
Av is your port area (height x width of the port face)
Vb is the internal volume of your box
Fb is the tuning frequency you want

Step 4: subtract half of your port width from your port length(Lv) to get physical Lv

Step 5: now you need to figure out how long your second wall is gonna be, so pick ANY number shorter than pLv. you can do this because your displacements always gonna be the same no matter how deep your box is.

Step 6: now take your physical Lv and subtract the external depth ( the number you decided on in the previous step +1.5" for the mdf. ex: if you picked 12 then your external depth is 13.5) from it. now this will give you the length of the 2nd wall.

Step 7: take this length (step 6) and multiply it by your port width+.75 and then multiply it by your internal height and finally divide by 1728. this gives you the displacement.

example, your 2nd wall length is 20", port width is 4", and height is 10"
so you get this 20*4.75 (since you need to add the thickness of the mdf to the port width)*10 for height/1728= .5497ft^3

Step 8: Now find the first wall length which is internal depth-port width. like in step 6 lets use 12. but this time since its internal depth we do not add the 1.5" for the mdf. example: 12-4=8. 8 is the length of your first wall. now do step 7 with these numbers to find the displacement. example: 8*4.75*10/1728=.2199ft^3

step 9: now find out how much your sub displaces by lookin in your owners manual or the company website. when you find out how much is displaces, well use .21 (15" xxx). so now you add all the displacements.

example: .5497+.2199+.21+(the internal box volume you chose earlier, well use 4 cubes) so the gross volume is 4.9796ft^3. this means your TOTAL box will be 4.9 cubes including port, this way your sub gets its reccomeneded 4 cubes (15" xxx in this example)

Step 10: Now we need to find out how deep we need to make the box in order for the sub to get its 4 cubes. well i know what your thinking...
"we used 12 inches for internal depth earlier in the example, how can it change now?" well like i said, displacement always stays the same so we just chose a number inorder to find the displacement, now we need to figure out how deep we need to make it to actaully fit within the 4 cubic foot reccomeneded volume.

so to do this we need to do the gross volume (step 9)*1728/(HxW).
example: 4.9*1728/(10x20) and we get 42.336. so the internal depth would be 42 inches for a box that is 10 inches high and 20 inches wide, in order for it to be 4.9 cubes total(gross volume).

Step 11: find the real port wall lengths.

for port wall one, its just internal depth-port width. example: 42-4=38" is your first port wall length.

for port wall two its your phyisical port length - (internal depth + 1.5")
example: lets say your pLv is 20 and your internal depth is 10 so you get 20-11.5=8.5". thats the length for your second wall.

and your DONE :thumbsup: . now of course all the numbers in this post are screwed up cause i was just makin them up as i was going along and not actually tryin to make a box, so the numbers wont match. either way try it out. good luck!

swimfreak26
11-05-2004, 07:48 PM
ttt for a good place for people to learn some things.

BASS OUTLAW
11-05-2004, 08:01 PM
P.S. I hate you ;)
Jmac do u also hate me 4 the sticky?? ;)

didnt u c the STICKY on the BOX construction. place.
u could have just added ur info ;)

OLD_SCHOOL
11-06-2004, 12:57 AM
It should be noted that you still have to know what you're doing :p:

I have a feeling it's going to be like when I posted this stuff and and people started complaining about how their enclosures sounded bad or kept PMing me to check over their designs ... I don't really have a problem with checking over designs, I just have a problem when I have literally a dozen or more requests a day to check over designs ... It was also frustrating because my actual design request count went down from about 2-3 a day to 3-4 a week ... So I basically went from making ~\$150 a week to ~\$35 a week ...

P.S. I hate you ;)

just say no.

IgnoreMe
11-06-2004, 11:29 PM
Jmac do u also hate me 4 the sticky?? ;)

didnt u c the STICKY on the BOX construction. place.
u could have just added ur info ;)
i did...but i read over it and i still couldnt design a box. so when i learned i decided to post step by step with lots of examples and make it as easy as possible for the person to actually succeed.

IgnoreMe
11-10-2004, 12:14 PM
Bump

req
11-10-2004, 12:50 PM
i havnt read this - seeing as im at work, but from the looks of it, its really in depth. ill have to give it a try. im planning on building a box for the next car i get (my dads) so i may try this out this weekend.

tune low + big port area + big box = loud as hell

ill post my thoughts on saturday when i give it a go. just gonna be rectangular with an elbow port most likely.

Zash
11-10-2004, 03:42 PM
Thanks for an awesome tutorial George

IgnoreMe
11-10-2004, 04:03 PM
your welcome. it should be noted that this is for L shaped ports. ports with MORE than 2 walls i did not write about. as soon as i have time, and i get help from a certain member of CA.com about how to do those again, ill post it up. but yea, this tutorial is easier with a little bigger boxes, and higher tunings.

LBX2G
11-10-2004, 07:05 PM
ok that is what i wanted to know too. was this tutorail for square shape ports.

IgnoreMe
11-10-2004, 07:11 PM
ok that is what i wanted to know too. was this tutorail for square shape ports.
by square shaped ports do you mean "slot port"? like a rectangular front face, with the port wall runnin in and then turnin in a L fashion?

LBX2G
11-10-2004, 07:38 PM
yeah, slotted ports

LBX2G
11-12-2004, 02:28 AM
so am i correct .

IgnoreMe
11-12-2004, 03:13 AM
so am i correct .
yup. slotted port ;)

sumone
11-12-2004, 04:49 AM
I'm experiencing deja vu...

IgnoreMe
11-12-2004, 11:36 AM
I'm experiencing deja vu...
i dont get it? what are you tryin to say?

Scarenius
11-14-2004, 11:26 PM
I've gone over these time and time again. I'd rather just pay Jmac to design one for me, just for the peace of mind. It'd take me days to get the design, and even then I don't know if it'd be right. It's worth the \$15, and it's not like you have to get a new one every month.

Of course, it'd better be a helluva box. If it sounds bad, I'll put the thing on JMac's lawn and go for 150db playing polka in the wee hours of the morning.

IgnoreMe
11-15-2004, 01:46 AM
you dont feel good about yourself that you actually learned how to design your own boxes? thats what does it for me. should always try to increase your skills imo

Scarenius
11-15-2004, 04:08 PM
Math skills have never been a high point for me. I mean, I'm already spending \$30 in materials for an enclosure that the nearest shop wants \$200 for. Is another \$15 going to kill me? Not really. I would naturally do the math myself, give whoever I pay the design so he can check over it and modify it as needed, but in the end, I take enough pride in knowing I built the box myself, I just didn't design it.

Trust me, I am capable of enough trades as it is. I'm typing on a computer I built myself, visiting a site I programmed myself (not caraudio.com, naturally), attached to this PC to a car amp attached to my XBox, with RCA cables I made myself running between. Outside is the car I repair and maintain myself, and inbetween in the house I'm building. If you don't believe me, I can get a digital camera and prove it all.

Penny wise, pound foolish and that, a ****** design will kill a custom built \$30 box, wasting materials and lots of time. A \$45 box, professionally designed, is significantly less likely to do that. Your instructions are good, no doubt. But in the end I will stick with what I am best at.

IgnoreMe
11-15-2004, 04:17 PM
Math skills have never been a high point for me. I mean, I'm already spending \$30 in materials for an enclosure that the nearest shop wants \$200 for. Is another \$15 going to kill me? Not really. I would naturally do the math myself, give whoever I pay the design so he can check over it and modify it as needed, but in the end, I take enough pride in knowing I built the box myself, I just didn't design it.

Trust me, I am capable of enough trades as it is. I'm typing on a computer I built myself, visiting a site I programmed myself (not caraudio.com, naturally), attached to this PC to a car amp attached to my XBox, with RCA cables I made myself running between. Outside is the car I repair and maintain myself, and inbetween in the house I'm building. If you don't believe me, I can get a digital camera and prove it all.

Penny wise, pound foolish and that, a ****** design will kill a custom built \$30 box, wasting materials and lots of time. A \$45 box, professionally designed, is significantly less likely to do that. Your instructions are good, no doubt. But in the end I will stick with what I am best at.
whoa whoa whoa. i never called you a liar lol. im just sayin that imo its always good to have an infinate amount of knowledge. im in no way doubting you of your abilities or skills. if you feel that its better to spend the money and get designed by all means go that route. i was just thinkin it would be nicer to add something else to your repitaur (sp?) of skills ;) . maybe ill pick up spelling as my next assignment lol

LBX2G
11-16-2004, 12:28 AM
audiobahn has a couple of port calculator.

i do not kno if they are right or not so do no credit me on this.

http://www.audiobahninc.com/tech/Calculators/PortLengthCalc.htm

Jayhawkk
11-16-2004, 12:32 AM
Might want to brush up on those math skills if you're building a house :)

spr_f150
11-16-2004, 04:32 PM
Jmac,

YGPM

spr_f150
11-19-2004, 10:47 AM
^2 ........

Scarenius
11-19-2004, 12:46 PM
It's \$10, I don't have a lawn, and I offer to refund money if not satisfied ... ;)
I'll have so many dumb question you'll charge the \$5 for me being stupid. That or I'll end up with some really weird request you have to calculate 6 times over. Gotta wait til I buy subs, though. Hooray for the expensive holiday of Christmas.

Goldtaz1
11-23-2004, 04:13 PM
Step 3: Figure out port length using this formula
Lv = Av*1.84*10^8/[Vb*1728*(Fb/0.159)^2] - 0.823*sqrt(Av)

Lv is port length (what your solving for)
Av is your port area (height x width of the port face)
Vb is the internal volume of your box
Fb is the tuning frequency you want

It should be noted that the formula above is not totally correct.

The correct formula is Lv = Av*1.84*10^8/[Vb*(Fb/0.159)^2] - 0.823*sqrt(Av). Do you see where George multiplied by 1728? Do not do that, this formula is for the port length, not cubic inches of port. Other than that step there is nothing else I can see that is wrong.

P.S. It is also noted that even if you used the 1728 in the formula above, you will not receive the cubic inches of port.

IgnoreMe
11-26-2004, 01:18 AM
bump for any new guys willing to give a shot at designing their own box

mrray13
11-27-2004, 12:10 AM
tune low + big port area + big box = loud as hell

real quick here...

all that adds up to less power handling as well. well,the big box does. just because the box is bigger isn't necessarly going to make it louder, more efficifient yes, louder no, as power handling goes down the drain.

now for all u guys that are foing to ramble on about this big box being this loud and this big box being this loud.....i know of three small boxes that are world champions this year, two of those in two different organizations (these are people i know personally) and they tell me that more and more are going the small box, big power route.

also, the big port area equates to a longer port for a specific frequency. but it does lower the probablity of port noise.

my advice? read the owners manual on ur sub, if it doesn't have one, go to their website or call them...get the recommended volume and port size and tuning. basicly, ur box is designed ie: they recommend a 1.75ft^3 box for their 12 with 20in^3 of port tuned to 38hz. all u have to do is measure ur vehicle and do the math to see if u can squeeze 1.75ft^3 in there.......that's overly simple, but it's the basic idea.

oh yeah...the vodka and sprite are workin on me..lol :silly: :sick:

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:

LBX2G
11-27-2004, 03:55 PM
real quick here...

all that adds up to less power handling as well. well,the big box does. just because the box is bigger isn't necessarly going to make it louder, more efficifient yes, louder no, as power handling goes down the drain.

now for all u guys that are foing to ramble on about this big box being this loud and this big box being this loud.....i know of three small boxes that are world champions this year, two of those in two different organizations (these are people i know personally) and they tell me that more and more are going the small box, big power route.

also, the big port area equates to a longer port for a specific frequency. but it does lower the probablity of port noise.

my advice? read the owners manual on ur sub, if it doesn't have one, go to their website or call them...get the recommended volume and port size and tuning. basicly, ur box is designed ie: they recommend a 1.75ft^3 box for their 12 with 20in^3 of port tuned to 38hz. all u have to do is measure ur vehicle and do the math to see if u can squeeze 1.75ft^3 in there.......that's overly simple, but it's the basic idea.

oh yeah...the vodka and sprite are workin on me..lol :silly: :sick:

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:
well i totally get what u are saying, But those guys compete. Most of the kids here just get daily setups. Soooo 2 2,000 watt amps will not do very well. I mean alternator upgrades are not fun, when i could have used the money for spinners. Like i said before i am not disageering just supporting george.

reed8857
11-27-2004, 04:26 PM
well i totally get what u are saying, But those guys compete. Most of the kids here just get daily setups. Soooo 2 2,000 watt amps will not do very well. I mean alternator upgrades are not fun, when i could have used the money for spinners. Like i said before i am not disageering just supporting george.

Did not mean to qoute you but what part of Warner Robins are you from as I am form there my self or are you AF

LBX2G
11-27-2004, 04:55 PM
Did not mean to qoute you but what part of Warner Robins are you from as I am form there my self or are you AF
I stay out towards Bryon. 96 is right behind me.

oh and to Jmac thnx, but i am very smart. But I am just very impatient. I hate to proof read ****.

reed8857
11-27-2004, 05:08 PM
No kidding I am from Byron sort of thats where my parents live

LBX2G
11-27-2004, 05:27 PM
No kidding I am from Byron sort of thats where my parents live

oh ok nice :clap: :clap: :clap: :clap:

mrray13
11-27-2004, 05:57 PM
well i totally get what u are saying, But those guys compete. Most of the kids here just get daily setups. Soooo 2 2,000 watt amps will not do very well. I mean alternator upgrades are not fun, when i could have used the money for spinners. Like i said before i am not disageering just supporting george.

the three boxes i speak of can also be used daily, and sometimes are...

i understand where u're coming from, but a larger box doesn't necessarly mean better or louder. it's just something we need to get across...

some subs do better in large boxes with big port area, others do better in smaller boxes with smaller port area...for example, i had a memphis pr10 in 1ft^3 vented, 6in^2 of port, tuned to 38 hz ran off 70wrms..this in an x-cab silverado...most ppl thought i had 2 10's and 250 watts....

it is important to match the sub to the enclosure and the manufactorers have eliminated most of the guesswork on their products. are their designs perfect? no, but they usually are the best street beater box design for that sub.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:

DeepMag1c
11-27-2004, 11:07 PM
How do u get AV.......

jellyfish420
11-27-2004, 11:46 PM
it is important to match the sub to the enclosure and the manufactorers have eliminated most of the guesswork on their products. are their designs perfect? no, but they usually are the best street beater box design for that sub.

well what would you do if you had no recommened enclosure size, just a list of t/s parameters? could you find the size by the parameters?

LBX2G
11-28-2004, 12:04 AM
the three boxes i speak of can also be used daily, and sometimes are...

i understand where u're coming from, but a larger box doesn't necessarly mean better or louder. it's just something we need to get across...

some subs do better in large boxes with big port area, others do better in smaller boxes with smaller port area...for example, i had a memphis pr10 in 1ft^3 vented, 6in^2 of port, tuned to 38 hz ran off 70wrms..this in an x-cab silverado...most ppl thought i had 2 10's and 250 watts....

it is important to match the sub to the enclosure and the manufactorers have eliminated most of the guesswork on their products. are their designs perfect? no, but they usually are the best street beater box design for that sub.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:

u kno what i run that same sub. But i had an 12. I have cracked the dust cap. I kno the box is way to big...3cuft @ 45 hz....yeah i kno the guy from memphis told me that it was way to big. And i only got 145 watts going to it some ppl think it is 1 15 or 2 12s. and i have alot more space to presurize ( 1995 Jeep Grand cherokee). I not trying to argue but just supporting george. It make more sense to take up more room than to save an buy more equimpent.

mrray13
11-28-2004, 12:07 AM
well what would you do if you had no recommened enclosure size, just a list of t/s parameters? could you find the size by the parameters?

honestly, no, i couldn't.

there are programs out there that can get u close, such as bb6p (which i use now) and winISD (which i used to use). but mostly, i asked around, here on the boards, ppl that i knew used that particular sub, stereo shops and customer tech. even if the company doesn't post/print a recommended enclosure, i'm sure they will help u with the basics.

would i like to learn how? of course. but in this current world, unless ur building ur own sub or u've bought some off the wall brand, there are too many ppl and too many avenues to finding a recommended enclosure.

case in point, i just built a box for a 15" orion h2. i have neither seen nor heard this sub. the website recommends 2.5ft^3..but after talking to ppl who have/are using this sub, the enclosure was built to 3ft^3. a lower tuning freq was used as was a larger port. in their experience, this was the best daily setup for sql.

anyway, i'm rambling...lol :wowflash:

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:

mrray13
11-28-2004, 12:12 AM
I not trying to argue but just supporting george. It make more sense to take up more room than to save an buy more equimpent.

i know u're not arguing..it's all good. lol....

and some ppl will agree with u..no problem. i'm not saying that that is incorrect. i'm just trying to get across that there are more then one side to this dilemma.

depending on personal experience and opinion...u and i are both correct. it's all about how the person reading this wants to apply the info.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:

LBX2G
11-28-2004, 12:22 AM
i know u're not arguing..it's all good. lol....

and some ppl will agree with u..no problem. i'm not saying that that is incorrect. i'm just trying to get across that there are more then one side to this dilemma.

depending on personal experience and opinion...u and i are both correct. it's all about how the person reading this wants to apply the info.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:

yup man but how do u like ur sound splinter subs.

DBfan187
11-28-2004, 12:28 AM
case in point, i just built a box for a 15" orion h2. i have neither seen nor heard this sub. the website recommends 2.5ft^3..but after talking to ppl who have/are using this sub, the enclosure was built to 3ft^3. a lower tuning freq was used as was a larger port. in their experience, this was the best daily setup for sql.
3.5^3', 30^2" of port, 30Hz is what I would've done.

IgnoreMe
11-28-2004, 03:43 AM
How do u get AV.......
just choose a port area. you want 60 square inches of port? your box is 15" high? then you make a port that is 15" high(internal) and 4" wide. i usually use something like 60 70 or 80^2 of port. more then one sub? add more port area.

mrray13
11-28-2004, 11:14 AM
yup man but how do u like ur sound splinter subs.

i love the soundsplinter rl-p12 that is in my wife's car. which is running in 1.25ft^3 sealed off of a hifonics nemesis nx750d. it gets loud, low and stays clean. truely an awesome driver!!

3.5^3', 30^2" of port, 30Hz is what I would've done.

after talking to denim and hccafan, the 3ft^3 was determined to be the best overall enclosure. however, the 30in^2 of port was also recommended (i did use 29in^2, long story) and tuning is in the 30-31hz range.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :peace:

Strecker25
11-28-2004, 12:33 PM
well trying to figure out an spl box after my first step the physical Lv turned out to be like 213 for a 4cube box tuned to 40hz, lol back to the drawing board.

Thuracine187
11-29-2004, 01:12 AM
im gonna be making a box for my 2 12w0 in the near future. Its gonna be all 1 box with a divider so each sub will have about 2.3 cubic feet and its own port. the port legth is where i get the problem.

my max width for the whole box is 40in and gonna be using 3/4 mdf with a divider so thats 37.75 internal width

40 - 1.5 - .75(for divider)

each sub

width = 18.5
height = 16.5

port diameter = 5

when i plug all the numbers into the pL formula i get like 81.3in. that seems a little big to me. so if some could tell me if that is correct and if not point me into the right direction i would really appreciate thanx.

Thuracine187
11-29-2004, 06:53 PM
*bump* for some help

Nikuk
11-29-2004, 06:59 PM
what do you want to tune it to?

=0.159*(((AV*(1.84*10^8))/((Vb*1728)*(Lv + 0.823*(Lv^0.5))))^0.5)

jellyfish420
11-29-2004, 07:03 PM
assuming the 18.5 and the 16.5 are internal as well....you never said what you wanted it tuned at but 15" long would be 30Hz. and the higher up you go (tuning)would only make the port shorter.

Thuracine187
11-29-2004, 11:48 PM
opps didnt relize i didnt say what to tune it to

i want to tune it to 33hz sorry bout that and thanks for some help

jellyfish420
11-29-2004, 11:58 PM
33hz = 11.75in

Thuracine187
11-30-2004, 12:07 AM
could you tell me how you got that so next time i dont have to ask for help please

jellyfish420
11-30-2004, 12:13 AM
Av*(1.84*10^8)
______________ -(.823*sqrtAv)=port length
Bv*((Fs/.159)^2)

Av= port area(in^2) Bv=box volume( in^3) Fs=tuning frequency Sqrt=square root.

LBX2G
11-30-2004, 12:20 AM
yo jelly i am guessing this is for tube ports.

Thuracine187
11-30-2004, 12:20 AM
thanks again

for slot port right?

jellyfish420
11-30-2004, 12:22 AM
im gonna be making a box for my 2 12w0 in the near future. Its gonna be all 1 box with a divider so each sub will have about 2.3 cubic feet and its own port. the port legth is where i get the problem.

my max width for the whole box is 40in and gonna be using 3/4 mdf with a divider so thats 37.75 internal width

40 - 1.5 - .75(for divider)

each sub

width = 18.5
height = 16.5

port diameter = 5

when i plug all the numbers into the pL formula i get like 81.3in. that seems a little big to me. so if some could tell me if that is correct and if not point me into the right direction i would really appreciate thanx.
5" port diameter...and diameter isn't used for slots. so i just assumed he was using pvc or something...

Thuracine187
11-30-2004, 12:25 AM
need lenght for slot port sorry that i wasnt clear about that

Nikuk
11-30-2004, 12:25 AM
tube, slot, triangle, whatever... shouldnt matter in the math. You just need port area and total port displacement.

jellyfish420
11-30-2004, 12:26 AM
thanks again

for slot port right?

you didn't say slot. but a 16.5x2" slot would be 29" long still tuned @33Hz, but now with alittle over double the port area.

LBX2G
11-30-2004, 12:29 AM
**** jelly what program are u using or are u doing this all in ur head.

Thuracine187
11-30-2004, 12:30 AM
im lost now

jellyfish420
11-30-2004, 12:35 AM
Bbp6

jellyfish420
11-30-2004, 12:37 AM
im lost now
whats up???

jellyfish420
11-30-2004, 12:38 AM
im lost now
whats up??? where you lost

Thuracine187
11-30-2004, 12:41 AM
just dont see how i cant get those numbers for the length. im pretty sure im doing the formula correct

jellyfish420
11-30-2004, 12:45 AM
just dont see how i cant get those numbers for the length. im pretty sure im doing the formula correct
well when you do the formula what number are you using for you port area?
you said 5" diameter but thats not area...is that what your using?

DBfan187
11-30-2004, 12:45 AM
Bbp6
I don't know what I would do without it...eh, I'd probally bug the **** out of Jmac.;)

jellyfish420
11-30-2004, 12:46 AM
I don't know what I would do without it...eh, I'd probally bug the **** out of Jmac.;)
don't get me wrong i can do it on paper...but i'm already sitting at the computer. its just easier to push a few buttons:):):)

DBfan187
11-30-2004, 12:48 AM
don't get me wrong i can do it on paper...but i'm already sitting at the computer. its just easier to push a few buttons:):):)
Oh, I can too. But you'll just have to get back at me in about a month.

Thuracine187
11-30-2004, 12:48 AM
im using 82.5 16.5*5 maybe i should go get some paper cause im using my ti-83

jellyfish420
11-30-2004, 12:51 AM
come up with like 60-70 inches?

Thuracine187
11-30-2004, 12:53 AM
like 81

jellyfish420
11-30-2004, 12:53 AM
he man you got aim? it'll be easier to talk on there?

Thuracine187
11-30-2004, 12:58 AM
ygpm

LightningStryk7
04-30-2005, 02:00 AM
bump for someone

IshbOO
05-02-2005, 10:16 PM
im trying to design a box now with this method and I'm having trouble finding out my second wall length. I get a negative number everytime I try to do so.

outside 16x33.5x20
inside = 14.5x32x18.5

Port
14.5x3

Fb is the tuning frequency you want: 34hz
Vb is the internal volume of your box: 4.0cuft
Av is your port area (height x width of the port face): 14.5*3 = 43.5 < meets minimum of 20in per sub for port area.
Lv is port length: 18.41

18.41 - 1.5 = physical LV(portlength) 16.91

step 6 + 7
16.91 - (10in + 1.5mdf) = 8.41

(8.41 * 3 .75 )(14.5*) / 1728 = 0.26^3 displacement

First wall 15*3.75(14.5)/1728 = 0.44^3 displacement

.18+.18+.2199+.44 = 5.0199^3 box size, after displacement

depth 18.5

wall one 18.5 - 3 = 15.5
wall two 16.91 - ( 18.5 +1.5) = -3.09 << ?

any help? plz thanks

does this mean i dont even need that second wall? or what im confused?

DBfan187
05-02-2005, 10:38 PM

Insomniac119
05-03-2005, 11:02 PM
like it was said before, the formula isn't going to get your dimensions with the snap of a finger, you have to know how to use it.

I'll have to figure it out because i'll be building a ported box in the neer future, and i've never tried it before.

IshbOO
05-06-2005, 02:12 PM
finally got my box all calulated thanks alot george, by the way how can I find the total square area of my box, so I can go buy the wood tomm :) sq ft.

Harrison486
06-03-2005, 08:18 AM
Step 10: Now we need to find out how deep we need to make the box in order for the sub to get its 4 cubes. well i know what your thinking...
"we used 12 inches for internal depth earlier in the example, how can it change now?" well like i said, displacement always stays the same so we just chose a number inorder to find the displacement, now we need to figure out how deep we need to make it to actaully fit within the 4 cubic foot reccomeneded volume.

so to do this we need to do the gross volume (step 9)*1728/(HxW).
example: 4.9*1728/(10x20) and we get 42.336. so the internal depth would be 42 inches for a box that is 10 inches high and 20 inches wide, in order for it to be 4.9 cubes total(gross volume).

When you say 10 inches high and 20 inches wide, are these the internal or external dimensions of the box?

I have been following this tutorial well, I am just confused on this one spot