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Help me tune my box?

 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 228
Registered: Jul-07
You would be doing me a huge!!! favor i'm looking into building this box i'd like to make it ported but but it may be a little difficult to tune... anyway here is a rough draft of the box i have designed it has approx. 2.6 cu ft which should leave me in the desired range if i can go ported..
[IMG]http://i44.photobucket.com/albums/f49/shaq_n_wade/subroughdraft.png[/IMG]

i'd like it tuned to around 32hz if possible. Again any help would be greatly appreciated guys..

(if i'm unable to get it done i'll go sealed and shrink the box down a little bit.) let me know what other info you might need.. oh and also if the port could be below the sub where it goes down 10.5 inches. anyway if someone can help me out i'll be very grateful and post pictures of the build (:
 

Silver Member
Username: Alonzoub

Post Number: 200
Registered: Apr-10
Since i don't know how beefy a sub your going to use or how much power your plan on putting to this thing... this is what I can do for you...

Starting with exactly 2.6 cu.ft of volume... In order to tune to 32 Hz:
Using a 4" ID port, Port Length: 13.5", Vb: 2.48 cu.ft.

Using a 5" ID port, Port Length: 22.5", Vb: 2.28 cu.ft.

Using a 6" ID port, Port Length: 42", Vb: 1.76 cu ft.

These are kind of rough numbers as they don't account for end correction. Hopefully it helped a little.
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 229
Registered: Jul-07
It's a Fi q 12" powered by an ed nine.1 so roughly 1200 watts rms

sorry i didn't really understand that at all is their anyway you might be able to show it a picture or something?
 

Silver Member
Username: Alonzoub

Post Number: 201
Registered: Apr-10
What I meant was, if your current design is (for the sake of calculations) EXACTLY 2.6 cu.ft with no port. The previous numbers i stated would be the port sizes and lengths needed to tune to 32Hz:

We can go ahead and eliminate a 4" diameter port because that's not enough port area for you. So you are left with 2 options.
(I re-ran the numbers with end correction for a bit more accuracy)

Use a 5" diameter port, make it ~19"-20" long
OR
Use a 6" diameter port, make it ~35"-36" long

catch my drift? You can put it anywhere in the box that you want to, as long as the diameter and length of the port is satisfied.
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 230
Registered: Jul-07
Somewhat i'm still a little confused.. by diameter do you mean it has to be a circle port? and why is the one with a larger diameter also longer? Still a little confused right now what i'm guessing at is...

Make a port opening (i'd like it to be square) 5 or 6 inches wide with 35 inches of port area.. correct me if i'm wrong.. (and like what type of width x height would the port opening be?

sorry if this is completely off but i'm pretty new to box's and all the terminology I've only done 1 previous set up.

Thanks for your help so far though!
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 231
Registered: Jul-07
i found 12volt port calculator. And not sure if i did it right but going here... http://www.the12volt.com/caraudio/boxcalcs.asp#por and using the slot port calculator.. i did a 5"w by 3" height and box volume of 2.2 cu ft (i'd like to bring it down a little to the manufactures recommendations) and a tuning frequency of 32 it said something close to 14.75" of port length. If this seems right to you i think i might do that since a square port would be alot easier for me to do... Thoughts? does this sound correct?
 

Silver Member
Username: Alonzoub

Post Number: 203
Registered: Apr-10
Sorry for not posting sooner, been a little busy. So basically, I want to make sure you understand that when adding a port to a box of known volume, the volume of that box is going to change once you put a port in it depending on the size of the port of course.

That being said, that port is way too small. A 5" x 3" port is only 15 sq.in. of port area. You said before that you want around 35 inches of port area, which makes more sense.

Here is an example. Lets say you make the port 7" wide by 3" tall, that gives you 21 sq.in of port area... given that information and an ASSUMED 2.6 cu.ft box to start with... Iterate through some formulas real quick and I find that in order to get a 32 Hz tuning with a 7x3 port and a GROSS volume of 2.6 cu.ft the port must be 22.25 inches long... having a port of this size will leave a Net volume (Vb) of 2.1 cu.ft in the box.

Note: Gross Volume is the volume inside the box as a total, Net Volume is the volume inside the box MINUS the port. Also the larger you make the port area, the longer the port is going to be to maintain tuning, therefore less Net volume in the box. So your in sort of a catch 22... make the ports rea too large and you lose too much volume in the box... make it too small and you get port noise and loss in output...

If you come up with another port size you want me to run the numbers for feel free to post it.
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 232
Registered: Jul-07
okay thanks for the response... i forgot all about the port volume and all that.. here are some new designs i came up with let me know if this would work....

http://i44.photobucket.com/albums/f49/shaq_n_wade/subbox1.png

it's 2x16 so 32 port volume correct?

and using 12volt calculator it says to have 27.75 port length, my designes above have 26.25 but i should easily be able to hadd the remaing 1.5 inches to one of the above ports depending on where i see my sub sits in the box...

Is it okay to have my ports like that? to have more than one?

Thanks again for your help so far..
 

Silver Member
Username: Alonzoub

Post Number: 208
Registered: Apr-10
Your drawing confuses me lol. Are there 3 ports??? Also yes a 2" x 16" port will give you 32 sq.in of port area.
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 233
Registered: Jul-07
haha sorry it was drawn very quick haha 4th of july you know haha. but yes 3 ports.. is that okay? or would that not be 32 sq in of port area because their are 3? in which case i would just need to shorten them tell it's in my area.
 

Silver Member
Username: Alonzoub

Post Number: 209
Registered: Apr-10
So you have 3 ports... each being 2"x16"?? that would be a total of 2*16*3 = 96 sq.in. of port area? Also you can't (at least to my knowledge) make the ports different lengths.

I think I see what you did here though... did you take the calculation of a 26.25" long port and divide into a 3 different ports of varying lengths? If so, you can't do that lol. The way a port works is that it will resonate at a certain frequency given 3 parameters... Port Area, Box Volume, Port Length. Changing one of these variables will change the frequency it resonates at.

In your case you calculated for a port with Port Area = 32 sq.in; Port Length = 27.75"; Box Volume = 2.6 cu.ft

These parameters will give you a port resonance (tuning frequency) around 32 Hz. Now when you go and chop the port length, the resonance of that port is going to change (its going to be higher if you chop the port).... Also since your ports are of varying lengths they will all resonate at different frequencies, I have never tried anything like this but I can bet it will sound awful.

After running the numbers, if you start with a 2.6 cu.ft box, it will be nearly impossible to tune that thing to 32Hz with anything over 24 sq.in of port area, the box is just a bit too small.

If you want to go with a rectangular port, my suggestion would be something like a 10" x 2" port that is 22" long, this will leave a net volume of 2.1 cu.ft. and 32 Hz tuning. Or that 7" x 3" example I gave before. You can snake the port around the box to make it fit but be sure to 45 all of those corners in the port turns.

Is it at all possible to make the box larger to allow for a bigger port?
 

Gold Member
Username: Joebruce

Crescendo Audio FTMFW!!!, AA Havoc 15 ... Your Mom FTW!!!

Post Number: 3507
Registered: May-04
Why do you have to build the box at those angles like that? It would be a lot easier if you just made a regular rectangular shaped or square box. Just plug in your dimensions in this calculator and adjust the port length,width,etc to get the tuning you want and it will give you the dimensions to cut the wood. Very easy tool to use. And all you would have to do is walk in to Home Depot or a place like that with the dimensions it gives you and have them cut it for you. While you're there pick up some wood glue and screws,maybe a few clamps and carpet or paint and go home and start building!

http://www.reaudio.com/LPort_Box_Calc.php
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 234
Registered: Jul-07
Twiztid, a box formed around my trunk will just make it look really clean and a more professional look so id thoose angles is how the back of my trunk looks so it will sit flush. (I Drive a 04 crossfire if uve ever seeen their trunk space.)

Alonzoub, haha k thanks im learning a ton about ports so far.. so im going to try again with one single port of 2x16 and see if I can" snake it to where it is going to fit... where u say to make the angles 45 degress.. (not sure how to explain this..) is it each corner on each side? So if the port was to turn at a 90 degree angle like an L would both sides of the turning point be made into a 45 degree angle? Or just the outside one?

Sorry if that doesn't make sense.
 

Silver Member
Username: Alonzoub

Post Number: 211
Registered: Apr-10
It would be better to have both sides 45 degrees but the ports I normally design only have the outside of the port 45'd and the inside of the corner I would round off. Like this: Upload

as for a 2x16 port, you wont be able to tune it to 32Hz with a gross volume of 2.6 cu.ft. You will either need to make the box bigger or make the port area smaller.
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 235
Registered: Jul-07
Thanks for the picture.

I think understand it all. I'm gonna see what i can do as far as the design with the current 2.6 cu ft (the port area can bring it down as far as 1.8) and if i'm unable to make it fit i'll see if i can't expand it a little and hey if all else fails guess i'll go sealed :/

Thanks again i'll put my designs up to make sure i didn't make any more additional mistakes once i figure it out..
 

Silver Member
Username: Noob101

Taylorsville, Utah USA

Post Number: 236
Registered: Jul-07
so i think i may have found something that worked...
1.5 height by 23.5 width port(the length of my box minus the .75 for the wood.. i measured it out to 28.5 port length (i'll give you my measurements to check if it's alright.) i just may have mismeasured my port since i'm not sure how to measure it... sorry if that's confusing hopefully my picture will clear it up...

http://i44.photobucket.com/albums/f49/shaq_n_wade/subbox2.png

The measurements you see (of 10.5,9, and 9) are the peices of wood with the first one being bigger do to the MDF board (it will be double baffle on all the outside to give it a flush look.) with those measurements i get 28.5 inches i need 30.78. so my question is with it "snaked" like that do you add the .75 of the mdf board making up each port? if that is the case i'm right at 30.75. if not once i set my sub in i'll see how much i can add to the top port to get it their.

Note: sorry i didn't show it in my picture but the opening to the port is on the very bottom (also don't know if this is okay.)
 

Silver Member
Username: Alonzoub

Post Number: 213
Registered: Apr-10
I hate to rain on your parade even more... BUT... I have read that making the h:w ratio of the port greater than 8:1 can cause port noise, even with enough port area. I am not going to tell you that it won't work, because I have never tried it, but when I design a box a try to keep the ratio much closer.

In your case, 23.5 / 1.5 = 15.666 ... so your ports h:w ratio would be 15.6:1 which is nearly double the recommended max.

Im not going to say don't do it though, if someone else would like to chime in with some experience on the subject, please.


On another note, that setup will have you tuned in the low 40's. Your port volume is (23.5)*(1.5+.75)*(28.5), that is (Port Width) x (Port Height + port wall thickness) x (Port Length). So your Port volume comes out to be .87 cu.ft. So now to get the Net Volume we subtract the port volume form the gross volume.

Vb = 2.6 - .87 = 1.73
So your box parameters come out as the following:
Net Volume: 1.73 cu.ft
Port Area: 35.25 sq.in.
Port Length: 28.5 in

Plug those into your calculator and you will get your tuning. Should be low 40's. This is why I said you need a bigger box or less port area. Once you get a massive port like this one, it will take too much volume away from your box.
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