Porting my box

I havent gotten far enough on the boxes to figgure out the volume, but i dont think i need it for my questions.

Can i make my box with a hole for a premade port (3" dia.) and when the box is done and i figgure out the volume, just use the calculator for the length that i need to tune it to the frequency that i want?  I was also wondering what frequency would sound best, i have a sealed box already with 2 subs so i sorta want it to play what the sealed box wont play as loud.  i read that a lot of ported boxes are tuned to 30ish Hz,  does that mean that notes at 30 hz are the loudest?  I havent ported anything before and i dont want a half @rse job as i didnt like the sound of my previous cheapo bandpass box.  thanks for any help on this.

Can i make my box with a hole for a premade port (3" dia.) and when the box is done and i figgure out the volume, just use the calculator for the length that i need to tune it to the frequency that i want? 

No, because the size of the box will be dictated by the volume of the port.  You have to add total port volume to the enclosure volume.

I was also wondering what frequency would sound best

Let's look at the subwoofer you intend to use.  First, is it designed to be used in a vented enclosure?  Second, the parameters will tell you what the best tuning frequency should be.  What does it tell you in the manual?  With the benefit of some experience with design programs, I highly recommend that you become familiar with one of them before getting out the woodworking tools.  WinISD Pro is probably the simplest to master.

 

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Wow...actually i still have to figgure out which subs i will be using in the end when the setup is complete, i downloaded the program...i still have to figgure it out a bit, but i think i'll figgure out which subs i want to use and then go from there.  If things start seeming to complicated for me then i might just change the box desin a bit and go with another sealed enclosure...although thats not as much fun.  I'll look around online to see what kind of sub I'll go with and then figgure out the progam, although if u said its the simplest to master then it shouldnt take long.  I actually didnt realize that some subs were designed to be used in a vented enclosure...

As a side question...is it possible to have a sealed box that is too small and properly figgure out how much damping material to use to make the box 'appear' to be the same size?  or isit just a matter of adding bits at a time?

Thanks for the help and the link to the program stevdart.  I appreciate it alot.

Allright...i decided that i'll go with MTX subs as i have MTX amps anyways...I'll be going with the RT10-44 subs, the specs arent in the program that i downloaded, but i think i can figgure out where to put the info.  they have an Adobe Acrobat file which has all the dimensions for a vented box, but its square...is there a way to figgure out dimensions and port size from the diagrams.  I'll try to figgure something out, but any help is greatly appreciated.  if i get the box volume the same, can i make the port the exact same as in the diagram, or will the fact that the box isnt actually a box (all curvy n stuff) mess it up a bit?

       http://www.mtx.com/caraudio/products/subwoofers/TechData_RT10-44.pdf

I did a rough measurement on the box and if i were to do it sealed it would come out to about 0.6 cubic ft. 

a sealed enclosure built by MTX was a mere 0.75 ft^3...i could easily make the box a little bit bigger if i wanted to go sealed.  but the vented box has a net internal volume of 1.45 ft^3, does that mean that my vent has to be made to compensate for 0.85 ft^3?  if so can i use the port size calculator to figgure on my port size?  the tuning frequency should be 35.3Hz (it doesnt have to be totally exact does it, can i round it to 35 HZ and still get the same quality?)

without using the program yet to figgure anything out, I figgure if my box is .6ft^3 and i need a .85ft^3 port to make a total box volume of 1.45ft^3 then all i have to do is add a 2" dia. x  6" long port to get my box right and the frequency of 35.3Hz.  Assuming that this is correct (believe me i would be very surprised if it was) then how do i get a round port equation to make a rectangle port so i can figgure out some math on making a thin rectangle port along the bottom.

please let me know if i screwed up...thanks.

I'm going to take you back a couple notches here.  The first thing I would do when choosing a sub for a particular type of enclosure system is to look at a couple of the T/S parameters:  Fs, Qes and Qts....before I start reading the manufacturer's suggestions on box types to use.  First, use Fs and Qes in this simple math:  Fs / Qes = EBP.  That sub is Fs= 35.3, Qes = 0.67.  So, 35.3 / 0.67 = 52.  An EBP in the 50's and below would work best in a sealed enclosure.  To second that, look at what is said on the DIY Subwoofer page.  Then look at the Qts specs of the woofer.  This MTX is 0.625, which you see is regarded as a design for a sealed enclosure.

I don't believe it is in your best interest to proceed with plans on venting this sub.  As your choices are still wide open, and I think it's a good idea to continue on your quest to learn to build a vented box, you should continue to look for alternative subs.  Look for a Qts in the .3 - .5 range, then do the math with the other parameters as I showed you.  So, pick an appropriate sub first, then go from there.  You'll have a more realistic-sized box volume and port displacement, and an overall better quality build.

And one other thing:  how much space do you have available ( in cubic feet if possible)?

I already tried to max the cubic feet for the boxes to get the best fit in the trunk without running into problems.  I could change a few things still and extend the sub itself out a couple inces from the box.  I could probly get around 1ft^3 with some redesigning.  U stated in the DIY Subwoofer page that the best results are mostly gotten with a sealed enclosure...should i be reworking my box design to see if i can get the appropriate ft^3 size for a sealed box then?

The box i already made with 2 - 10" jbls are 1.2 ft^3 per chamber,  i dont have specs for the subs cause they arent manufactured anymore and i bought em at a closing sale (no papers) i will also try to find a sub that will work best with that box as well...I dont care anymore about having 4 of the same subs, rather i would like each box to have the right sub for the application.  but a higher Qts and a lower EBP is what i want then for the sealed box right?

the JL Audio 10w1v2 - 10" sub looks promising...the Qts is .405 and the EBP for it is 58...and the box specs for it are 1.0ft^3 ported tuned to 31hz...or even 6.25ft^3 for sealed which is what i have now...but i'll continue working on the vented box.  Seems like the perfect sub to me.  http://www.jlaudio.com/press/W1v205.html

So with this said, do i make the box 1 ft^3 and make a port for it with the port length calculator...which would be at 2" dia. - a 7" long port....therefore making the perfect box for the sub and setup tuned to the required specs of 31Hz?

Still a little confuzing...but hopefully i'm getting somewhere.  I really appreciate your helping me out stevdart.

Thanks for posting Mike...I doubt I'll ever be known as a "Vented Box Man" (which is good so u can keep your title)I love the setup u have now...whoever gets to sit on that seat is gonna be completely numb from the vibration, lol..i had my 2 jbl subs under the seat with just a 240W pyramid amp ( which i fried a little while ago cause i wanted it to put out more BASSSS,lol) and even that made my a$$ numb after 15 min of driving, lol

Your right about the sleep...i'm pretty wasted and my mind is going nuts trying to figgure things out, lol.

With my boxes that i'm working on now being quite close to the recommended volume, and the ability to only increase to about 1 ft^3 is it a bad idea to vent or will i still see benifits of venting?  Gotta remember i still have a box with 2 subs (1.2ft^3 per chamber) and it pounds like a MOFO as it is...so even if i have to turn the gain down for the other 2 subs i'm fine with porting  if it still has its benifits of giving me different tones and notes that the sealed box wont give me....and the ported box size for the sub is only 1ft^3 which i can most likely do.  Is it worth it?  Can i do it? 

I'm off to get some sleep.  thanks for your info and advice guys...i greatly appreciate it, and i hope to learn more...thanks again....g'nite

You really should care about that above all else.  Take a breather on this and search through this forum for threads dealing with the subject of mixing subs.  You might want to just rethink your approach...sell what you currently have, or replace the subs and turn the box into a vented box for something else, or.....?  If you want a 4 sub setup, you should approach it in that light, not in the light of adding 2 more subs to what you already have.