Enclosure Size Calculation

How do I determine the optimum enclosure size for my sub?  Is there a program that I can input its thiele parameters into?

Ive got a Jensen xs1212 12" sub.  the document that comes with it isnt too good.  it suggests 1.5ft for best response in a ported box, but the number seems kina arbitrary.  Would it be better to go bigger?

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

I find this page to be helpfull for calculating ported boxes.

https://www.carstereo.com/help2/Articles.cfm?id=5

this one might be helpfull for sealed boxes. Reply back here if you need more help or questions. Many expert people here always glad to help.

thanks for the links. 

Im gonna build  a 1.5 foot ported box for the following reasons:

1. its my girlfriends car so she wont be listening too loud.

2. the subs are cheap!

its gonna be in the trunk (obviously).  should i put the port onto the backside, facing into the back of the seat?  or in the front, facing into the trunk?

Ok guys, thanks for the program.  its definately a sharp learning curve!

So the box is looking more like 1.1ft. or 38.1L!  

Now this program lets you "optimize your curve"  which is great, if you know what you want the curve to look like!  when I first input the data & hit go, the tuning frequency was 9.5hz.  Is that right?  Ive put it up to 38.1Hz, as that is the Vas value of my sub.  Which one is right?  Or should I tune it for some magical value in the middle?

Oh, & one more question.

The program doesnt take into account the volume of the speaker itself or the vent correct?  Should I add on 0.07ft to the box to make up for this, or just leave it as it is?

Okay, now we are starting to get somewhere.

The reason that the program computed 9hz is probably because there were 2 parameters missing.  Ill show you what I got
Fs 38.1hz                         Vas 2.2ft3 (63.1L)

Qts 0.38                           Qms 10.13

Qes 0.4                             Xmax 0.157" (4mm)

Pe RMS 175W (575W max)               Re 3.49ohms

Sd 64.3"   (415cm2)                   Cms   0.257 x 10^-3 M/N

Mms 2.43 oz  (68.79g)

Bl   12.03 Tm                     SPL 91db

Ill keep playing with it, but I want to start building this unit in the next couple of days.  Id like to do it right though...

Right

Im missing the Le & Z values.

Also Im unsure as to which diameter to input

Nom Dia  9.02" (229mm)  or   VC dia.  2"  (51mm)

Also, the Usable Frequency Response is 20Hz-1KHz.  Would i set the graph cut-offs to these values?

Its interesting that the program wants all the values in meters!

I appreciate all the help.  One of the reasons I went with cheaper hardware is to learn how to do it right, with my girls car as the guinea pig.  That way when my own ride gets out of the shop...

I'll look at this later when I have more time, but meanwhile:  if the program shows l for liters, and you want to input cu.ft., place the curson on top of the l, click through the measurement changes....so in reality all conversions will be done for you by the program.  That is in the parameter input dialog box.  Also, the cursor changes can be made when you bring your project up in its own box.

Don't worry about Le, and Znom is the nominal impedance of the driver ( e.g. 4 ohms).  That sub has a 4 mm Xmax??  That's the typical excursion of a 6" driver!  Just see what size sealed box you can make for it.

Set the program low to 20 Hz, and the high can be anywhere 500 Hz and above for subs.

LOL

Before everyone starts cruising on my crappy components, just remember that the idea here was to use this as a learning experience & ive been learning heaps already.  Not to mention coming in well within budget.

I recalculated everything for a sealed box & came up with 0.982 ft^3, so it should be right around 1ft^3 when I take the volume of the speaker into account.  I dont plan on bracing it as it probably wont need it!

Ive heard some different theories on deadening material, but I was gonna use dynamat or something similar & line 3 adjacent sides with it.  Would packing in fiberglass be better?  If so, would I pack the box up with it, right next to the speaker, or just use a bit?

EBP?  Where do you find that & what does it represent?  Can you tell me how you got those values for volume, ports, etc?  I havent gotten anything close to that!

Maybe you could send me the save file?

By the way, im using WinISD beta, if that makes any difference.

EBP is Fs / Qes which gives you a value that determines what type of enclosure works best.  38.10 / 0.4 = 95  . The EBP comes up in the center of the second dialog box after you select your driver from the scroll down list.  That box gives you the program's determined type of enclosure and shows EBP=95.3  Generally, an EBP of 50 and below is best sealed, and 90 and above is best vented.  In between numbers, which a lot of subs fall into, can go either way.

To edit your driver database, pull down Utilities, database editing.  Select your Jensen from the scroll list and go to parameters...change whatever in it is entered wrong.  You'll notice the values you enter are a different color than the ones that the program determines (BTW, there is a check-off box to let the program determine values, check it).  When you enter parameters, there are some you should leave out...QTS and BL are two that I know the program wants to figure, because if you enter a value that is not identical to what it figures, you get an error box.  The parameters you listed in the above posts are all you need to enter, (leave out QTS and BL)  which is what I did.  The best enclosure and size came up automatically when I brought up the Jensen driver, and all I had to do was look at the graph and approve it and look at the port size and see if it was workable, which is with this sub.  The small Xmax allows for a small port length, so this is a pretty easy one.  And I'm using the same version as you.  You'll get it, take your time.  In fact, I have learned it better by helping out guys like you.

When working with the port size, you can change the port diameter to be exactly the inside diameter of whatever port tube you could find to purchase (e.g. PVC pipe, etc.).  You'll see the length change to accomodate the different diameter you entered, but the box tuning and size will remain the same.  And you can use the cylinder calculator on this site under Port Length calculators..to find the displacement of the port tube.  Make sure you add it to the overall air volume along with driver dispacement so that you get a net air space of 2 ft^3.

Oh btw, I just entered the Re, and not the Znom.  The program figured it to be 6 ohms.

So Ive gone through again & my EBP does come out to 95.3.  There are a few differences though.

For Volume I get 1.806ft^3  & for Tuning I get 40.5Hz.  Ql = 7 (?)

The Port is 4.02" x 8.38,  & the Vent Mach=0.08

All of my inputs seem right, however, when trying to edit them & leave out Bl & QTS, I do not have a box which allows the program to calculate the numbers.  This must be making the difference.

If I manually input 2ft^3 & tuning of 38.67hz like you said, the port length is 8.27 instead of your 8.35"

Im gonna try to download a different version to see if it makes a difference.  I want to have the box designed today so that I can get the materials tomorrow.

The version I'm using is the current one that is being downloaded, version 0.50a7 (11-09-2004).  The "auto calculate unknowns" check box is in Utilities, Database Editing, Driver Editor at the bottom of the box.  But what you have listed as the design is very similar to what I got and will work just fine.  Mine has 4.02 diameter as default, too, but I changed it to 4" even, and the port length changes because the volume is slightly different.  This is something you can play around with a little and each change will result in a slightly different looking graph output.  What I showed you has a flatter response than the one you came up with, mostly because of the extra air volume.  You could build it either way and be successful.  The port tuning can be either, so feel free to use what the program shows you.

Pe is RMS value of 175W.  The 575 is a meaningless number.

Alright

Ive come up with a box that measures (internally) D1=6" D2=10.8"  H=11.5"  & W=35.5".  The Vent is 4" x 8.1".  This will give a total volume of 1.986ft^3, with 0.1ft^3 taken into account for the volume of the driver, vent & wiring pot.  The tuning will be 39.96Hz.

Im gonna triple check my figures, then go get the supplies.  Exciting!

Ive massaged it a bit so that it will fill the trunk as I had hoped.  Im gonna place the sub on the left side of the box, & cover the whole thing with a 5/8" amp rack, which will make the sub fit flat, & will hide all the wires.  Should look pretty good.  Ill post pics of my progress.

Thanks for all the help!