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View Full Version : round port ft3 =/= slot port ft3? And a Fs ?



ummduh
09-14-2012, 01:14 AM
I'm working on a box for my car. 2005 Mustang GT.

Anyways, the box calc at bcae1 recs a 2.4628 ft3 box, with a 4" round port at 18.53" length, which calcs out to 0.135 ft3 of volume.

If I'd rather have a slot port, can I simply make a slot port with the same volume of the cylindrical port? Or does it not work like that?

Second, my sub has a Fs of 23.6.

Doing a lot of reading on here it seems most peoples' Fs's are in the mid to high 3x's.

What does this really mean to me?

This is my first go at a ported box, I usually do sealed cuz.. well, they're hard to fawk up.

Sub is a ReAudio SRX12d4, BTW. Amp for the moment is a RF 400.4, will get a proper monoblock when $ permits, and I tend to listen to rap, metal, "rapcore", and classic rock.

Kangaroux
09-14-2012, 01:20 AM
Fs doesn't mean jack once you drop a sub in the box so don't worry about it.

Port length is a function of box volume, port area and tuning. However, aero ports (cylindrical) are more efficient than slot ports, and thus require less port area to achieve near the same results as a slot port.

Also, a 4" port thats 18.5" long and a box volume of 2.5 cubes means youre tuned at 25hz which will be WAY too low for you. I suggest aiming for around the 35hz mark, in which case you would need a 4" port that is only 8" long.

ummduh
09-14-2012, 01:26 AM
Is the field "Fb" the tuned freq on there?
edit: eh, it won't let me adjust that field anyways.

Thanks for the help.

Kangaroux
09-14-2012, 01:30 AM
Is the field "Fb" the tuned freq on there?
edit: eh, it won't let me adjust that field anyways.

Thanks for the help.

Fb is your tuning frequency, F3 is like the -3dB mark below your tuning frequency or something like that...basically it is where your box's response begins to roll off on the low end.

Rule of thumb for tuning frequency is try to keep it above like 30hz. Anything below 30hz and you don't really gain that much low end, you just start losing overall output and all of your high end. I had a box tuned to 27hz, adjusted the port and brought it up to 32hz. The low end response didn't change but it was overall louder and just more pleasant sounding. You don't need to tune low to play low. I'm tuned to 32hz and can play down to 20hz no problem.

ummduh
09-14-2012, 01:33 AM
Sweet. You sir are a gentleman and a scholar. haha, but seriously, thanks a ton. I've got about a hundred browser windows open and things are starting to blur together.

Tomorrow, I start building.