Originally Posted by Mfusick
I think I made the port 55" long but I can't remember exactly...
I am trying to reverse engineer this to determine exactly what "tune" I have on my port but I am struggling since I am not sure about a few things. Here is what I remembered : (I changed some in build process)
I think I am going to make it 24" deep by 24" wide by 42" tall. That is about 14 cubic feet before the port and speaker.
The port will be 21.75" x 4" (24" wide minus 3/4" each side+ 3/4" brace down center) and run the full width and depth almost. It will be about 38" long - (24" deep minus 4" = 20" + go down about another 18" to get me to about 38" or whatever exact I need for a 20hz tune)
I figured the port would take up 38"x22.5"x4" [3.16666' x 1.875' x .3333' ] or 1.979 cubic feet. <--- DID I DO THIS RIGHT ???
Minus the woofer puts me around 11 cubic feet I'm guessing after bracing- I'll look closer at it when I get to the port length to get it exact. 38" puts me about 21hz I think
I don't think I used a port length of 38" thougt. I thought it was 55" - which I think was because I made the box volume different, or I had calculated it wrong.
I just took a look at the box volume calculator here:
I entered in 24" Wide by 24" Deep X 42" TALL
Then I entered .75 for the material thickness.
Bracing volume I entered 360 inches/3 ( I think I figured this was 4" wide x .75 material by 24" long times 6 of them) this seem right for about how much bracing volume it should be ?
Port Volume I used 4500 inches/3. This again was a guess. I factored in 21.75" x 4" x 53" = 4611 (or something like that I remembered)
Drive volume = .3
Drivers = 2
The calculator spits out about 8.99 cubic feet volume with these figures. So it appears my box is about 9 cubic feet of volume. Anyone see anything that is a mistake or wrong above ^ ? Or does that look about how is should ?
If I did make the port 53" long then my tune should be pretty close to 20.5hz right ?
You think this is something I could measure by putting some white out on the cone and watching for the least excursion and what frequency it happens at ? Is that really accurate?