big RSD box

[slc72005]

ok here is the exact volume of my box


box (not counting port displacement)=2.78cf

port volume=.42cf with 37.8 of port opening area


box volume with port volume=2.35cf



when i use this port freq calculator http://www.carstereo.com/help/Articles.cfm?id=31

im not sure if in the bix that says box cf if youare supposed to use just the box volume total without the port or if you take box volume and subtract port volume

if i do the calculations using the box size (not with the port are subtracted) it says that my tunning freq is about 34.5hz

if i fill it in with just the box size (subtracting port volume from box total volume) i get a tuning freq of about 37.5hz


or to make it easier and see if anyone has a box calculator that knows how to use it (because i sure dont)

my box volume is 2.78cf without subtracting for port volume

the port volume is .42cf ( the port measures 2.75 inches wide X 13.75 inches high X 19inches long

with a box this size how long should the port be to tune it low for the RSD sub so i can get some more lowend authority out of it (make the peak low)

thanks

[BH]

I'm a big proponent of large well sealed enclosures but if you must port it when you state the box volume you are supposed to subtract the vent volume.

Also you need to specify the diameter of the port you'd like to use if you want to simply know vent length. If/when someone does the calculations all they'll be able to provide is a vent area (or they'll give you a length and a diameter (which is the same thing as vent volume)).

[slc72005]

I'm a big proponent of large well sealed enclosures but if you must port it when you state the box volume you are supposed to subtract the vent volume.

Also you need to specify the diameter of the port you'd like to use if you want to simply know vent length. If/when someone does the calculations all they'll be able to provide is a vent area (or they'll give you a length and a diameter (which is the same thing as vent volume)).

the port area is 37.8 inches (its a slot port)

then volume without subrating the port volume is 2.78cf

witht he port volume subracted it is 2.36cf

the port i have now measures 2.75inches wide by 13.75inches tall (so a port area of 37.8square inches) and is presently 19 inches long


i gave all measurements because the point of the thread is to get the port length so i can lower the tuning of the box, so i need to make the port longer so i have a lower peak and have more authority in the low end

[BH]

There ya go... Now you have enough data in the thread to solve the problem.

[brenzbmr@sb]

okay
looking at what you provided me and that the port is made of
3/4 mdf

and you are using one side of the box as one side of the port and the fact that the opening is 2.75 but you gotta add the displacement of the 3/4
piece of wood that is building the other side of port your port actually takes up 914 cubic inches

so inreality your box is 2.23 cubic ft give or take with port and speaker.


at 2.23 your box is tuned at roughly about 45 hz

now this is off the info you provided.
if you need to tune it lower you need to actually make a new box
i would do it in about 2.25 and tune at about 32hz
you should notice a lot more lower end
i have the same 12 at my shop(oh yeah impact and i opened up our shop,
jan 1)

and we have it in that box and it is a very nice woofer

pics up the lows pretty damn good. give me a holla for more box tips and
also for advise.

oh and i just pickedup another ti elite.

i wanna run them in 2 cube sealed apiece for shits and giggles

also send me a pic of your blown ms2125 with rev number(i need one more ms2125 to make this work)
thanks

[slc72005]

i'm not building another box. this one will have to do.

i just want to take this box and extend the port length to lower the tuning

can someone tell me how much longer i should make the port?

i can extend it up to no more then an additional 20 inches if need be.

doing ruff figures if i were to extended it an additional 20 inches i would still be well within PG specs on the box

[brenzbmr@sb]

yeah but as you put more port in the box it will change the internal
volume(smaller) then as teh box gets smaller to tune the box low that port is gonna get longer.

to tune it at 32 hz at 2.3 cubic ft will be 37 inches long
but you gotta add that extra displacement of 866.00 cubic inches

makes your box now 1.79 but again at 37 iches will not be 32 hz
in other words the port needs to be longer.

the only othe option is to put the difference in measurement which would be 37-19 on the outside of the box so not to change your internal measurement.

that is why its eaiser to make a new box.

or the second thing to do is make a new box and go with a smaller opening on the port so that it wont be as long.

i hope this helps but again make a new box if you want to tune lower
or we can modify your existing port to tune lower by sectioning off a part of the port.
if you are willing to do that then ill calculate for you a tuning for 31 hz
which will keep theport at 19 inches but you will have to divide the port
and then seal off the difference(make it removable from front so you
can change the tuning for musical taste, did that to a set of 15s years ago)

let me know
aloha

[bdubs767]

http://www.psp-inc.com/

[brenzbmr@sb]

yeah but he wants to keep his original enclousure and port size.

but that is something to look into.

they take up way less displacement.

[bdubs767]

I actually posted the website for it's port calculator....but thus are nice ports and look a lot better IMO then slot ports.

[slc72005]

never used areo ports before, do they sound as good as a slot port?


the easiest thing to do would be to cut wood to fit in the port to make the port openning smaller

to keep it simple i can use 1inch mdf to put int he port to make it smaller, since i have a pretty big port opening losing some port area wont be a problem

so how many layers of 1 inch mdf ont he bottom of the port will i have to add to make it tuned lower to about 30hz.

if my calculations are correct each 1 inch layer of mdf that i add to the port would be shortent he port area by 52.25 inches

any thoughts?

thanks for your help guys

[HoseHead]

Post your drawings, please. Lots of good info here, but difficult to apply without a model.

Us box building virgins want to know. And plus I'm a dopey Canadian, so pictures help lots.

HH

[VW337]

Without reading a book here--

Scott the volume of the port you have provide is that the port internal volume or external volume as in the outer dimensions of the port and port material, this will make a difference. Simply because if I calculate it using .75" MDF I get a displacement of .462 plus you have drive displacement of .14 so your internal volume after this is all removed is 1.751 cuft given your total value of 2.35cuft.


In this instance here is what I suggest--

make the port opening smaller, to 1.25 x 12.25, if my calculations are right this means add a layer of .75" MDF to each internal side. Then Extend the port to 24 inches. These steps should significantly smooth out the reponse you are currently getting.


current graph--


After suggested mods--

[bdubs767]

please do the mod, your curretn box is boom boom box

[stipud]

Holy jesus that is some pointlessly high tuning right there.

You could just seal the port altogether.......... (I'm not kidding)

[BH]

Holy jesus that is some pointlessly high tuning right there.

You could just seal the port altogether.......... (I'm not kidding)

I'd go there...

[slc72005]

Holy jesus that is some pointlessly high tuning right there.

You could just seal the port altogether.......... (I'm not kidding)

I'd go there...

i hat sealed boxes sorry

[BH]

Then you probably don't want to flatten out your response too much... If you hate sealed boxes and like the sound of a ported box its that big hump that you like....

[bdubs767]

Holy jesus that is some pointlessly high tuning right there.

You could just seal the port altogether.......... (I'm not kidding)

I'd go there...

i hat sealed boxes sorry

add a second sub sealed....more output and have better esponse then your boom boom port box.

[bdubs767]

Then you probably don't want to flatten out your response too much... If you hate sealed boxes and like the sound of a ported box its that big hump that you like....

scott go sealed, to have more bottom end then and just do some eqing w/ your eq232 to get some of the db spike from the ported box.

[BH]

Then you probably don't want to flatten out your response too much... If you hate sealed boxes and like the sound of a ported box its that big hump that you like....

scott go sealed, to have more bottom end then and just do some eqing w/ your eq232.

Thats a good way to cross input thresholds and end up w/ all sorts of nasty stuff.

[slc72005]

Without reading a book here--

Scott the volume of the port you have provide is that the port internal volume or external volume as in the outer dimensions of the port and port material, this will make a difference. Simply because if I calculate it using .75" MDF I get a displacement of .462 plus you have drive displacement of .14 so your internal volume after this is all removed is 1.751 cuft given your total value of 2.35cuft.

no, the internat volume of the box is 2.78cf thta is if there was no port in the box.


my port measures 2.75inches X 13.75 inches X 19inches long. 1 side of the port is along the wall, so the volume of the port witht he 3/4mdf included comes out to .53cf

so inside box volume with port volume subtracted is 2.25cf then subract .14 for sub displacement you get an internal volume of 2.11cf after everything is said and done


i have a pretty big port for the RSD so i would like to put a few pieces of mdf int eh port to shrink it down a bit as that seems to be the easiest way to do it.

[slc72005]

scott go sealed, to have more bottom end then and just do some eqing w/ your eq232 to get some of the db spike from the ported box.

the eq232 is only running to the ti elites, so that wouldnt work

[BH]

I run a box a lil bigger than 2 cubes sealed and love it.

[slc72005]

i hat sealed boxes sorry

add a second sub sealed....more output and have better esponse then your boom boom port box.[/quote]

i had 3 10 rsd sealed up, didnt like it