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View Full Version : Box Calculator Vs. Moe



kickerlivinloud
11-13-2006, 07:31 PM
Ok, here's the prob I've run into. I've trying using a couple differnet calculators to tune boxes I've been designing. Out of ceriosity (sp) I tryed putting one of Moe's boxes into the cal. Only 1 big problem, they don't match. I used RE's "L-Ported Speaker Box Calculator" and this one... http://www.subwoofertools.com/forum/ported-box.asp?Ew=35&Eh=12&Dia=4&Xmax=16&Vd=.1&NumW=1&Vb=1.03&Fb=45&Qts=&Vas=&Fs=&CE=0

I also had used another one but I can't find it now, it was very close to the one above.

Now I know Moe is most likley the one who is right but he told me about and to use the RE calc, so I would assume he trusts it. I know a lot of ppl are going to say do it the old fasion way and I guess I'm gonna have to learn that way. I've seen the formula and quite frankly I can't make heads or tails of it. I know the tuning has to do with the following...

Vol of the box vs. Vol of the port

Now making the connection is were I don't have a clue. If someone would take the time to really explain how to PROPERLY find the tune of a box I would greatly apprceate it!!!! I'm just tired of using calculators to later find out they are not giving me proper tuning...

My SN is in my sig if IM would be easyer then responding

Thanks!


Jon

xluben
11-13-2006, 08:11 PM
http://www.diysubwoofers.org/misc/portcal.htm

but it's metric if that bothers you :(

moe and subwoofertools are pretty much spot on (and both right) in my experience.

with subwoofertools the xmax value controls port width. also, moe left quite a bit of extra volume for driver displacement in most of his designs.

j3bus2k3
11-13-2006, 08:13 PM
RE's calc is flawed. IIRC, it doesnt account for driver displacment...

xluben
11-13-2006, 08:14 PM
proof (my box):

moe's design (3.5ft^3 @ 32Hz, w/50in^2 of port):

http://i107.photobucket.com/albums/m305/xluben211/box%20build/35cubes32hz50sqin6lw.png

subwoofertools:
http://www.subwoofertools.com/forum/ported-box.asp?Ew=32&Eh=14&Dia=6&Xmax=14&Vd=.08&NumW=2&Vb=3.5&Fb=32&Qts=&Vas=&Fs=&CE=0

hmmm, looks the same to me :)

kicker06
11-13-2006, 08:38 PM
subwoofer tools uses XMAX to determine port area BTW.

Just thought I would throw that in there.

Subwoofertools is a good site IMO. Worked twice for me, so A+ for it!

iceteebone
11-13-2006, 08:40 PM
is end correction figured into that re calculator?

the link doesn't work for me :crap:

xluben
11-13-2006, 10:27 PM
subwoofer tools uses XMAX to determine port area BTW.

Just thought I would throw that in there.

Subwoofertools is a good site IMO. Worked twice for me, so A+ for it!

already mentioned the xmax trick :)

but i do think it's a good site.

it does have problems showing the correct image for a straight port (no bend at all) when the port is long (it shows the port not connected to the front baffle), but i believe the numbers it outputs are still correct.

it also is hard to get a good design with any straight port (even if the box image is correct). it will alter the box width you entered to make the tuning correct while still giving the proper port area.

with enough fiddling you can make it give you good design :) (for most boxes this is not an issue)

if you know what width, height, driver displacement, volume, tuning and port area you need (or at least what would be acceptable) it is a GREAT tool.

if you don't really know what you are doing, it's easy get a crappy box design :crap:


is end correction figured into that re calculator?

the link doesn't work for me :crap:

i believe it uses an end correction of 0.732

like this:

http://www.diysubwoofers.org/graphics/port.gif

EDIT: link isn't working for me either. site was fine when i posted the link, but now it won't load :confused:

kickerlivinloud
11-13-2006, 11:45 PM
RE's calc is flawed. IIRC, it doesnt account for driver displacment...

It was off a lot more then that. I ran 5 different ones and the tunning was normally off 4-10 Hz and the volume wasn't even close.

Exluben: Thanks for the link, I tried a couple on that one and they were off too. Wierd???


Thanks guys, idk why I didn't get "subwoofertools" calc to work. I'll have to try it again..



Jon

kicker06
11-13-2006, 11:55 PM
I used my exact box specs on the RE and Subwoofertools site. I got a .2cu ft differece as well as a 3hz difference in tuning.

RE had a .2cu ft bigger box (due to driver displacement not being there) and the tune was 30hz, where as on subwoofer tools, it was 33hz.

Just account for driver displacement on the RE Calc and you'll be fine.

kickerlivinloud
11-14-2006, 12:05 AM
Ok, to make sure I got this right... Here is what I came up with. Not even close to what the RE calc gave me (imagine that)

http://www.subwoofertools.com/forum/ported-box.asp?Ew=46&Eh=8&Dia=2&Xmax=19&Vd=.06&NumW=1&Vb=2.34&Fb=45&Qts=&Vas=&Fs=&CE=0



2.34^ft3: Net volume
.12^ft3: Port volume
1.47^ft3: Final volume


How does that look? Makes me wonder exactly what my box is tuned to right now. Scary thought!



Jon

kicker06
11-14-2006, 12:38 AM
Those Calcs make no sense...

2.34-.12 doesn't = 1.47 btw

kickerlivinloud
11-14-2006, 12:51 AM
Those Calcs make no sense...

2.34-.12 doesn't = 1.47 btw



Sorry, i missed a step...

2.34 is total volume

46*8*11=4048/1728=2.34----Total volume
44.5*9.5*6.5=2747/1728= 1.6--- 3/4" MDF displacment
24.4(port area)*9.75(port lenth)= 237.9/1728=.13----Port Displacement
1.6-.13=1.3 (messed up on the first one, blah!!!!)


I hate math but I am good at it when I really try. This make a little more since now???


Thanks

Jon