box tuning

[RAM_Designs 5,000+ posts]

oh and just to clarify 2.6 is not a random number it's the chamber where the sub is in not including the port

3.75 is total area including port

2.6ft^3 with three 3" aeros = 15.75" each, plus an inch for the flares, so 16.75" each from flare to flare.

edit: nevermind I thought we were talking about three 3" aeros.

 

[wenn_du_weinst 10+ year member]

trooofff. your need more boxx recalculate your box by taking the port and finding its displacement then add that to the sub displacement, and bracing displacement, and your net volume, and you have your gross. thats how you get your last box number i usually figure out my depth last

that is what I was saying only difference is box needs to be 2.6 not 3.75

 

[SicAudio 5,000+ posts]

we dont care about all that we just want to know:

3.75 gross

after double baffle and sub it is 3.6 cf gross

port is 12.5 x 3

how long does it need to be for 35hz

thats it no aeros or other stuff.

please dont post anything but what port length u have based on that info only.

 

[SicAudio 5,000+ posts]

ttt

 

[RAM_Designs 5,000+ posts]

we dont care about all that we just want to know:3.75 gross

after double baffle and sub it is 3.6 cf gross

port is 12.5 x 3

how long does it need to be for 35hz

thats it no aeros or other stuff.

please dont post anything but what port length u have based on that info only.

So 3.6ft^3 after sub displacement. 12.5"x3" port that's 27" long(like the other guy suggested) is ~.8ft^3 worth of displacement, which is a little short of the 1ft^3 he'd need to get down to the 2.6ft^3 figure he's working with. I'd personally just make the port 12.5"x3.5" and 32" long, then you'd have 2.6ft^3 tuned to 35hz(according to the carstereo.com calcs, which are right on with what winISD gives me) like what wdw was suggesting. 3.75ft^3 with a 12.5"x3" port will need to be 17" long, like you were suggesting, but apparently the 3.75ft^3 is before any displacement...correct?

Sounds like you're not accounting for port displacement. //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

 

[SicAudio 5,000+ posts]

carstereo .com cal says 16.36 with 3.6 volume. u cant account for the port displacement til u have a fving port to displace!

after port the box vb is 3.16

 

[SicAudio 5,000+ posts]

anyone else? where is pv or fasfocus or cianzo or moebius **** it lol

 

[RAM_Designs 5,000+ posts]

carstereo .com cal says 16.36 with 3.6 volume. u cant account for the port displacement til u have a fving port to displace!
after port the box vb is 3.16

You use net box volume to find port length, not gross volume. The way I do it is, let's say I have 6ft^3 to work with for a pair of 12's, and I already know my dimensions that I'm using. Basically I set aside a certain amount of volume for the port, which for something like this will be in the 1.5ft^3 range so that I can keep the net box volume that I'd need after all displacements. So now I know that I'm using 4.5ft^3 tuned to whatever I want, so I just tinker with port dimensions until I find a length that gives me the amount of displacement I need, in this case 1.5ft^3...and voila.

Also, in your argument, the program would have no idea how to account for the port that you may be building. There are too many other variables that will determine how much space your port is taking up(ie: thickness of wood, doubled up port walls, number of exposed sides inside the box, turns, etc.).

 

[SicAudio 5,000+ posts]

so verify that or prove or disprove the finding i have.

better yet how long does the port need to be in a box that is 3.6cf if the port is 12.5 x 3" and tuning needs to be 35hz.

 

[SicAudio 5,000+ posts]

Fb = 0.159*SQRT[(Av*(1.84*10^8)]/(Vb*1728*[Lv+(.823*SQRT(Av))])

LV is the length of the port

AV is your port area

VB is your boxes internal volume(every displacement accounted for)

Fb will be your tuning frequency once you work the formula through.

 

[SicAudio 5,000+ posts]

The tuning frequency of the enclosure is found by knowing the internal volume of the enclosure, the cross sectional area of the port, and the length of the port. If you what you want frequency you want to tune your enclosure to then you only need to know two of these to figure out the third.

Usually the length is the one out of these three that is found out last. What frequency you are tuning should be found out either by manufacturer's recommendations or by designing an enclosure in a design program. Once you know what frequency you want to tune to you will need to know the cross sectional area of the port. This is determined by how much air velocity is going through the port as well as the space available. You want a air velocity through the port low enough that you do not have port noise. You can figure out what cross sectional area to use the same two ways as the tuning frequency.

 

[RAM_Designs 5,000+ posts]

better yet how long does the port need to be in a box that is 3.6cf if the port is 12.5 x 3" and tuning needs to be 35hz.

I already answered that.

As for my evidence: http://74.125.47.132/search?q=cache:mriChcANXMIJ:www.clubknowledge.com/Car_Audio_FAQ/archives/4633.html+use+net+volume+to+determine+port+length&cd=4&hl=en&ct=clnk&gl=us

"We use Vb. Vb is the net box volume of airspace inside the box, after we subtract sub and port displacement values. "

"In all of these formulas to calculate port length, you're supposed to use the net internal volume."

It's also good to use common sense. If you think that you are supposed to use box volume before port displacement, then I can come up with a design that will yield negative box volume. How about a 1ft^3 box uned to 20hz with an 8" aeroport? It'll need to be 332" long, which as I'm sure you know will be more than 1ft^3 worth of displacement. A program cannot account for things like this, or what I mentioned before about variables that are involved with the port itself.

 

[RAM_Designs 5,000+ posts]

Fb = 0.159*SQRT[(Av*(1.84*10^8)]/(Vb*1728*[Lv+(.823*SQRT(Av))])
LV is the length of the port

AV is your port area

VB is your boxes internal volume(every displacement accounted for)

Fb will be your tuning frequency once you work the formula through.

Bingo bango.

 

[SicAudio 5,000+ posts]

and everyone on roe says u use after port displacement (VB ) to tune it but how the hell do u have net displacement without a port yet lolz

 

[RAM_Designs 5,000+ posts]

and everyone on roe says u use after port displacement (VB ) to tune it but how the hell do u have net displacement without a port yet lolz

I already answered that. You must not be reading.