Question on cabinet porting

johnnybass01 · #1 01-13-2012, 02:42 PM

Hi all i have a couple of silly questions on cabinet porting. I have a 210 cab that I really like but it is shaped like a cube and the drivers are offset. it's stock dimensions are 20.5"x20.5"x15"deep it has a claimed frequency response of 40hz to 16khz and has one port (it's a triangle) and is 10" across the bottom and has a height at the center of 5" . this is what I want to do. I want to build my own vertical cab with dimensions of 15"wide x 28" to 30" tall and make the depth whatever it needs to be to get the equal cubic feet of the original cab. The question is will i get the same tuning by using 2 triangle ports half the size of the original say 5"x 2.5" or do I stick to the same size i have now.

**mikeddd** · #2 01-13-2012, 02:49 PM

In theory you can get the same tuning by using two smaller ports which equal the volume of a single larger port. The problem you run into with small ports is "chuffing". That's the "chuf-chuf" noise you hear when the woofer is moving a lot of air thru the port, but the port is too small to keep up.

That's not saying you absolutely will have that problem, but it is quite possible you will, being that you're looking at moving to smaller ports.

That's about 5% of your answer, because that's all I know.

Others will chime in. Good luck.

johnnybass01 · #3 01-13-2012, 02:58 PM

I know i am probably crazy for wanting to do this in the first place, But i have been playing around with the whole foam fiberglass composite construction and really want to do this. the cab right now is 48lb's with ceramic magnets and i think in theory i can get it down to about 30 lbs . plus i use a gk mb800 micro so having a smaller footprint makes it worth it to me.I think to equal internal volume my new cab will have to be 15"w 28"t not sure on the depth though.

**mikeddd** · #4 01-13-2012, 03:03 PM

Cabinet design is very complicated. It really is a lot more than just figuring airspace and port sizes. I'm no pro, but I built tens of subwoofer boxes of all shapes for car audio. Some sounded awesome. Some sounded like they were full of sand, even though the airspace was right. LOL!

Depending on the dimensions of the box, standing waves can form. Putting the port directly behind the cone of the driver is generally a bad idea. Those are just two of the things that come to mind.

will33 · #5 01-13-2012, 03:11 PM

15" deep. I assume you're talking about external measurements here? Otherwise, that is one huge 210. It's the internal that counts, make that the same and you can do whatever you want with the outside, panel thickness, etc. The larger the port is, the longer it must be to reach the same tuning. The space the port(s) occupy must be subtracted from the gross internal volume of the cab to have the correct net internal volume for the drivers.

johnnybass01 · #6 01-13-2012, 03:42 PM

those were external dimensions, the port on the cab now is just a cut in the baffle it does not extend in at all just the bottom corner of the baffle.

1n3 · #7 01-13-2012, 03:59 PM

Talkin' about one of these?

johnnybass01 · #8 01-13-2012, 04:19 PM

will33 · #9 01-13-2012, 04:41 PM

The baffle thickness is your port depth. For example, if the baffle is 3/4" thick, your port is 3/4" long. Build your new box with the drivers aligned vertically, make it the same total volume on the INSIDE as your current one is and cut the same size triangle in it and it's the same thing in a different shape. You can cut 2 triangles in the new one exactly 1/2 size of the single triangle in the current one and have the same thing.

johnnybass01 · #10 01-13-2012, 05:30 PM

thanks will33 that's what I wanted to hear. the cab there in now is 1/2" ply . the only thing that I don't know was taken into account on the cab their in now it the recessed handles on the side , i wont be using these just one dish handle or flush strap on the top.

wighat · #11 01-13-2012, 05:39 PM

Free program to calculate box volume, port, etc:

LinearTeam

will33 · #12 01-13-2012, 05:50 PM

Quote:

Originally Posted by johnnybass01

thanks will33 that's what I wanted to hear. the cab there in now is 1/2" ply . the only thing that I don't know was taken into account on the cab their in now it the recessed handles on the side , i wont be using these just one dish handle or flush strap on the top.

Handle cup doesn't take up enough space to worry about. It's in the realm of "no audible difference". You should run some bracing in there though and account for that.

johnnybass01 · #13 01-13-2012, 05:59 PM

i'm a mac user and can't access that.still looking for a good program for use with mac

will33 · #14 01-13-2012, 06:11 PM

Quote:

Originally Posted by johnnybass01

i'm a mac user and can't access that.still looking for a good program for use with mac

There are mac programs as well as programs that allow you to run windows stuff on mac but I don't know what they are. You should get some if you want to learn/persue speaker building but in this one particular case, if you build it to the same identical internal volume, port area and depth, same drivers, etc., you don't need the program. You're just re-making what you have in a different shape. There will be some slight differences in baffle step, internal panel to panel wavelength interactions, etc. but nothing you'd ever notice at gig volume next to a drumkit. If anything, it'd be an improvement simply because you'd spread more of your sound in a wider arc in front of the cab and have one driver a little closer to the ear.