Torres' Box Tuning Calculator - Updated 8/18

[audiogod9000]

Ay bro, i got a quick ''Q''

When i do it, it comes out with 17x40x24 = 7.77 (your calculator), but with math it comes out to 17x40x24-4.5(3x.75)=9.4 .

Why is that?

[Torres]

the gross volume in my calculator takes out the wood thickness. that's why under box dimensions it says outer dimensions so when you put in the measurements, it takes out the proper wood displacement. so your 9.4 is that whole box in itself, while the 7.77 is actual usable airspace before any other displacement. so basically the walls of the box take up 1.63 cubes of space

[audiogod9000]

the gross volume in my calculator takes out the wood thickness. that's why under box dimensions it says outer dimensions so when you put in the measurements, it takes out the proper wood displacement. so your 9.4 is that whole box in itself, while the 7.77 is actual usable airspace before any other displacement. so basically the walls of the box take up 1.63 cubes of space

Well i mean with the math i use it does just the Internal space. 17x40x24 - 4.5 (6x.75) = 9.4

[Torres]

yes...but my calculator automatically takes off the proper amount depending on the thickness of the wood before figuring volume. so you need to put in external dimensions. if you're using .75" wood, put in 18.5x41.5x25.5 and you'll get 9.44. the calculator takes off 1.5" off each measurement and will use 17x40x24 to find the volume

[Torres]

ive got a Q for you, how come when you check off, slot port everything changes? when you have the demensions already in for the port shouldent it calculate it the same? also when you check the port bends, why does it change the tuning and everything else? (also with that, where it says actual port length, it goes to a funny number) ive always used your old on you made, and just built my box's that way, but now im wondering with your new one if maybe i was building them wrong and they were not tuned to what i thought they were?

when doing a slot port, you get what's called 'end correction' which adds half the height of the port to the length, which lowers the tuning and effects net volume slightly. which is why you see things change. when the port bends, it doesnt need to be physically as long which also has a slight effect. you might not have been doin em wrong, they just werent as accurate. the more options there are...the more accurate it is. the update that i'm almost done with (just gotta debug and check for accuracy) pretty much takes into account EVERYTHING i could think of myself and with suggestions from others. so...it might not match that one either, but should be as good as it gets.

What is the formula that your calculator is using to compute the port volume, my hand calculations do not give the same results

make sure they are executed in the proper order.

[Decaf]

that formula does not involve port volume, its seems that your calculator is also including the top and bottom thickness in its calculations, in which the only wood thickness needed is the port wall if using a slot port and both walls and top piece if it is not

It is a common misconception that the tuning frequency (fb) is a function of port volume when in fact, it is actually a function of the port's cross-sectional area and its length as given by the formula:

Where Av is the cross-sectional area of the port (in square inches),

Lv is the length of the port (in inches) and

Vb is the enlcosure's net volume (in cubic inches).

copied from this

http://mobile.jlaudio.com/support_pages.php?page_id=165

[Torres]

more ideas to improve your calculator expo!

Few things I was thinking.

1)A way to plot the box's bandwidth and freq response.

2)Adding more exterior demensions, so that you can easily calculate "wedge" shaped boxes.

3)Allowing the ability to use 2, 3, or 4 ports. since sometimes when your using a round port you need multiples.

4)A visual layout of the box just for some added looks.

Might all be a pain in the ass, but i was just thinking a little

DAMN YOU! just as i was getting it all wrapped up! (i think) lol.

well...for #1 and 4, there's no way for me to do anything visual like that, not as of yet. i'm taking another semester of visual basic, so we'll see where that takes me. they have a section for images and graphics and whatnot, but i'm not sure what i'll be learning in this next class.

for #2, already got it got another depth for boxes like this:

and another height textbox for boxes like this:

as of now that's been the hardest part of debugging. i had first part right i think (havent checked it manually), but then when i'd add in another height for the second type box, the volume would jump from say 17 cubic feet to like 30+ somethin feet. i'd be like rearranged the coding 100 times, but then went through the coding itself and think i got it

and as for #3, i may be able to do that. adding in a radius/diameter box and a multiple port box wont be hard to do and figure in port area. i'll look into that

[EricR]

ok i have a question also.

here is a SS of each box, both identical boxes and port except on one the port is on the side, the other port on top. but they are identical ports so why is the tuning changing so much.

[Torres]

Sorry I'm still a little confused on this. I'm using this calculator also and ckecked slot port and port bends. My box is 22'' deep, port is 22'' long but it says (physical port length 16.5''). So since my baffle is part of the port I would cut one piece 15.75'' long and the 2nd piece 4.75''? I think that is correct just want to be sure before I start cutting. BTW box is 37W 17H 22D, port is 5.5x15.5x22long tuned to 37.--hz.

i think when i did the coding for the port length, i didnt take into account the proper displacement of the wood. doing in sketchup, i'm getting a piece 15" long. seeing as how the port bends, measure down the port and you'll get 22". here's a pic of what i mean:

add the numbers outside of the box in green and you'll get your port length

ok i have a question also.

here is a SS of each box, both identical boxes and port except on one the port is on the side, the other port on top. but they are identical ports so why is the tuning changing so much.

you have the 30 and the 8 switched on the port. if doing a slot port, the distance from the port wall to the box wall needs to go under port height or else a much bigger number will get added in for end correction in the port. in your case, one is adding 4", and the other is adding 15". port placement shouldn't change the measurements.

[Torres]

Thanks for responding to my inquiries. The math for wedge boxes isn't hard, I have built several myself. I am still a bit confused as to why the newer version did increase the net volume when the slot port option was checked. Is that the way it should be? I would really like to see the formulas you are using so if you wouldn't mind can you pm them to me. If not then I understand.

I figured out how to get bass box to roughly estimate my final net volume with my slot port but it is still off from what the new version reports as the final net volume. This is where I am really hung up on the most. Using outer dimensions to figure gross volume and then subtracting all displacements (port, sub, bracing, etc) would decrease the gross and yield the net. But even when using one wall of the enclosure as a wall of the port does it really add as much as .29 ft^3 over using a port that has four walls?

Do you plan on adding calculations for labryinth ports as well? Would be nice since I usually make my ports that way. The labryinth port issue is why I was saying the old version reported my final net volume correctly.

yeah the math isnt hard at all. it's easy to understand. getting it into the program to execute properly is the hard part. last time i tried, i was .26 cubes off on the calculator to the paper. i think i have 23+ variables just to find the volume of a box with 2 different depths. i dont mind PMing you the formula. i have the picture version posted here, and it's basically the same thing, just on one line with lots of parenthesis. it's more how i get the numbers for the variables in the formula. which are all through the program lol. but i'll PM them if you want.

one thing i didnt take into consideration when making the current calculator was port displacement. a port with 4 independent sides will have a different displacement than the same port with 1 independent side. small things like that make the difference, which i have added in the new one. i did not do a labryinth port however. there's so many ways to do ports, it's hard to figure in a way to do all of them. so if i do that, it will most likely wait till another update. also, straight ports are more ideal than a port with lots of bends, which is why i do displacement for ports like that.

I have a question about the port bending? If my port bends twice Should I subtract the port height from the physical length a second time? Only if the second bend uses a outside corner? My second bend DOES NOT Use a corner of the box but turns 180% into middle of the box. I think the 180% length of physical port length is the second port height I am refering to? I think I should NOT subtract any pysical port length for the second bend because I am NOT using an outside wall for the second bend? I think this is right just want to make sure. Also if I kerf one side of the port opening WHERE do I start measuring my pysical port length? I think it is where the port walls start being parallel or starts a constant width but want to make sure. I know to subtract the dispacement that the kerfed opening takes up. Thanks in advance.

correct. not needed for the second bend. and i've heard different things with the kerf ports. some say what you're saying, where they're parallel, and some say halfway from the parallel point to the complete open flare. i'm not 100% sure either way, but i bet the difference would be very small