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Old 03-21-2011, 02:57 PM
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Default Questions about building a fart box - Port area?

Hey all, I'm going to be building a 44hz fart box here in the next couple days and have a few questions regarding port area on such an enclosure.
I hear that with most of these types of enclosures you want a ton of port area and and a relatively high Fs.
Currently I have sketched up a 31Wx15Hx15D enclosure with a 4x13.5 port with enough length to bring me to roughly 44hz.
My question to you all, is that if this is way too much port area to have for such an enclosure? In this case, we are at roughly 24.5sqin per cube after port displacement. Is this far too much? When building this type of enclosure, am I better off sticking to 14-16sqin of port per cube, or heighten up to maybe ~18-20sqin per cube?
This enclosure build is for two Mach 5 SPL-12s off an Orion 2500D. Vehicle's Fo seems to be right at 44hz.


Thank you,
Ron

Last edited by Ronmeister; 03-21-2011 at 02:59 PM.
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Old 03-21-2011, 03:25 PM
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Learn to use enclosure software.
Port area is fine.
The 14-16 rule is dumb.
Dont tune exactly for your peak.
Youre using the terms incorrectly.
My microwave is calling.
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Old 03-21-2011, 05:40 PM
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Okay, do you have any recommendations then?
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Old 03-21-2011, 05:50 PM
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If your vehicles natural resonant freq is 44hz, you want to keep your box tuning slightly lower than that. You have to do testing, testing, and more testing to determing how much higher the boxs peak relative to thier tuning in your specific car. Example: My trucks natural resonant peak freq is 53hz, so I tuned my box at 45hz because I knew on other setups I would always peak roughly 8 hz higher then my box tuning. If i tune to 30hz, I peak at 38hz, etc. In your case I would say 37hz is a safe place to start so if you need to cut down the port a little to bump up the hz to dial in on the 44hz you can. I'm assuming you have tested your cars resonant freq with a sealed box flat response box ?
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Old 03-21-2011, 05:52 PM
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just build the shit and throw a big ass port in there and see what it does lol
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Old 03-21-2011, 05:55 PM
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Quote:
Originally Posted by surreal View Post
Learn to use enclosure software.
Port area is fine.
The 14-16 rule is dumb.
Dont tune exactly for your peak.
Youre using the terms incorrectly.
My microwave is calling.
I approve of this message.
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Old 03-21-2011, 05:55 PM
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In some cases it works out quite well mcmuffin^ lol
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Old 03-21-2011, 07:06 PM
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I had 50 sq in per cube in my "fart box" Seemed to work out ok.

If you're determined to try to hit your car's resonant frequency, 5hz below is a good place to start. i.e.- 39hz tuning for your 44hz res freq. I'd also like to know how you came up with that frequency though.
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Old 03-21-2011, 07:43 PM
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I found the Fo to be 44hz because of the countless daily ported and sealed enclosures I've had in the vehicle with the use of a friend's trusty TL.
Alright, I'll check it out. Maybe just do an 8" sonotube and see where it gets me. In this case it was a slotted port, but I guess it'd be much easier with a round port than can be cut down.
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Old 03-21-2011, 07:49 PM
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Quote:
Originally Posted by mcmuffin View Post
just build the shit and throw a big ass port in there and see what it does lol
This pretty much sums up every serious competitors game plan.

There's slight rules to follow, but in the end all you can do is build it and see if it works.

I've thrown away 10+ "what if I try this" boxes.

It's just the name of the game.
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