first time trying to build a box

[rsfm089]

okay so I'm trying to build a box for 2 dc xl 12's yes i am jeff. but I've started the pen and pad and a 99 cent app. lol  

w39h14d20

sub displacement .38

port thickness 1.5

wood thickness 3/4

port width 3.25

port height 13.5

port length 25

net volume 3.44ft3 (dc calls for 3)

tune 32.74

port area 43.88in2

port volume 1.20ft3

port per ft 12.77in2

band width 24.55 hz-65.47hz

going for subs front port front. Port in the middle.  does this look right or sound right will be on about 6k trying to save to get a dc 7.5 but might buy a dd m5. anything that points me in the right direction is very helpful been through about thirty pieces of paper. 

[reedal]

Nowhere near enough port area

[rsfm089]

what kind of port area am i looking for every time i try to add port area it jacks my tuning into the high 50

 

[reedal]

No less than 82in^2, according to Triticum's Improved Port Area calculator (he has a thread with a link to that calculator on this forum). I haven't put anything into WinISD though, so I have no idea how the estimated port velocity and bandwidth is. His calculator recommends optimal port area at 112in^2. 

 

Its changing tuning because as area increases, length also needs to increase in order to obtain the same tuning, which also means your enclosure size needs to increase in order to keep the same enclosure volume. With a 44in^2 port, you will lose the majority of your output on 6KW. Triticums calculator recommends 82 at minimum, and I trust his calculator, due to him being one of the more active enclosure designers on this forum.

[rsfm089]

i can't find winiSd for mac. I can get up to 108.00in2 and stay at 3.67cft but it brings my tuning up to 43.17 and my band width comes out to 32.38-86.34 also brings my port area up to 29.46in2 thats like my max dimensions  i had 2 hdc12 in five cubes at 32 but joe x designed that box i don't understand how ppl make these numbers work 

[reedal]

What are the absolute max dimensions you have to work with? Is it what you said in the first post?

[rsfm089]

no max is 39w 15h 24.75d with those dimensions i come up with this 

port width 8.25  port height 13.5  port length 30  net volume 3.38 tune 42.77 port area 111.38in2  port volume 2.60ft3 port area per ft 29.10 band width 32.08hz 85.55hz. As a disclaimer i might be doing a couple things wrong like port thickness it is 1.5? and common pots walls 2? Btw reedal thank you very much for your help 

[reedal]

You're welcome.

I've tinkered with the numbers in Torres, but I don't like the port length. Maybe @Triticum Agricolam And @Joe X can help get you set up on the right path a little better than I can

[rsfm089]

Thank you very much first time ever trying to design one learning a lot thats for sure. I always thought it was plug in numbers and go. I was so wrong 

[Triticum Agricolam]

So the box you are trying to design is a pretty tough problem to solve, so don't feel bad that its giving you a hard time.  The issue is the incredible amount of power you are wanting to put into a relatively small box.  When playing content around the tuning frequency all that sound energy has to come out of the port and 6000 watts is a LOT of sound energy.  It needs space to do that.  I like to think of things in terms of watts per cubic foot of box volume.  At 1,000 watts per cubic foot is where it begins to get pretty challenging to get enough port area, in your case you are at 2,000 watts per cube, a tough problem indeed.  

When it comes to designing your box you have three competing requirements you need to try to balance: 1. getting as much port area as possible, 2. keeping the tuning frequency where you want, 3. keeping the port a reasonable length.  Number 3 is important because once ports get much over around 44" in length they can start to create problems due to port resonances.  No matter what you do you probably aren't going to get enough port area to keep port velocities down to where I like them to be.  You are just going to have to accept that you will lose some output to port compression and do the best you can.  The good news is you have plenty of space to work with.  

Here is one suggestion:

My suggestion is for a single port along the side, since that's the most efficient.  Is been my experience that the tuning frequency comes out a little lower than Torres shows, so it should be pretty close to 32 hz.  I wish you could have more port area than 64 sq in and I wish the port wasn't so long, but compromises are going to have to be made. 

This is just one way to tackle the problem.  You or someone else may come up with something better, but at least this is a starting point.