Measuring for resinate Freq:

[Lord Baccus 1]

i measured from the subs to where the mic go's and got 7'

give or take an inch.

so 7'x4=28' gives me the 1/4 wave

devide 1131 the speed of sound by 28'= 40.39Hz

so i port to 30.39Hz - with cabin gain should peek @ 40.39Hz

but what about the ports fireing 90degrees out of faze, ???

subs are pointed forward into the back of the seat & the ports are fireing up along the back window line.

i drive a 1988' Ford F-150 x-cab

Edited June 25, 2007 by Lord Baccus

[dopey 0]

Where did you learn to do that?

[almond 0]

from what i've read the distance from the back of the sub to the mic needs to be 3x the length as the distance from the sub to the mic. not sure where i read that, but it stuck with me. anything further than that i dont know

[///M5 2,833]

I lol'd

[theabunai 3]

I thought the best way was to build a single sealed enclosure that will dislpace the same amount of space as your ported enclosure..

have a Tone test cd.. then go tone by tone and test each freq. Keep volume set at the same level at all times. Have all doors and windows closed. use a db meter to record the decibels...

the frequency with the highest decibel is your magic number...

I could be wrong...

Edited June 26, 2007 by theabunai

[vladd 26]

i think that it is even more than that. I'm sure someone more SPL oriented will know, but i thought you had to take the sealed box and test it outside (where vehicle doesn't change the freq) and see where it peaks, and then compare that to in vehicle response

[theabunai 3]

Vladd you could be right...

but wouldn't you have the box freq by using the QTC you made the sealed enclosure with, then taking the vas, QTS and Fs to get the enclosures Fb (enclosure resonance) ?

I could be wrong again though

[mrray13 30]

i think that it is even more than that. I'm sure someone more SPL oriented will know, but i thought you had to take the sealed box and test it outside (where vehicle doesn't change the freq) and see where it peaks, and then compare that to in vehicle response

this is the technique i've read about. measure a sealed enclosure (of roughly the same overall gross displacment of yoru spl box) outside the vehicle first.

then place inside the vehicle in roughly the same location the spl box will go, and face. then measure again.

but for the life of me, i can't remember what you do next, lol. it was stickied here once, but might have been lost in the upgrade...

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[Adrian_D 520]

Where did you learn to do that?

you learn that stuff in physics class. it's just a basic formula.

[Lord Baccus 1]

Where did you learn to do that?

http://www.ozaudio.com/docs/SPL_Theories_and_Tips.pdf reading is a great tool

opps i let the secret out

[tejcurrent 13]

That was a very interesting link

I'm insterested in how subwoofer and port directions effect that. I can see the practical application of a front firing wall, but I have crx style boxes in my yukon, and I wonder how to figure the distance with that?

Have you had success using the formula they give (I guess so being that you say you're going to finals, just wondering how accurate it is).

[Tommythecat 0]

My god....those are some of the most hideous "white papers" I've ever seen.

Back away slowly.

[Lord Baccus 1]

My god....those are some of the most hideous "white papers" I've ever seen.

Back away slowly.

please explain ? whats a white paper

[dopey 0]

Where did you learn to do that?

http://www.ozaudio.com/docs/SPL_Theories_and_Tips.pdf reading is a great tool

opps i let the secret out

LB...would you like me to point out the flaws with the math in the second part of that, or can I just they're wrong?

[Lord Baccus 1]

please any info would be helpful as i am about to port my box

i have my boxx ported @ 54Hz & it Peeks @ 62Hz on a Hott day & peeks @ 65Hz on a cool day

the resonant freq of my truck is 48Hz but ill be Dammad if i can get it to hitt @ that Freq....

i was going to try porting to 38Hz for Street Beat...

butt according to this formula im hitting too High ???

i meeter on the drivers side Kick - behind the emergency break... only place i can get the mic to stay put

Edited June 27, 2007 by Lord Baccus

[vladd 26]

everything i've ever heard says you want to tune below the resonant freq of your vehicle, I'd try something around 38-40hz and see how that works.

[dopey 0]

please any info would be helpful as i am about to port my box

i have my boxx ported @ 54Hz & it Peeks @ 62Hz on a Hott day & peeks @ 65Hz on a cool day

the resonant freq of my truck is 48Hz but ill be Dammad if i can get it to hitt @ that Freq....

i was going to try porting to 38Hz for Street Beat...

butt according to this formula im hitting too High ???

i meeter on the drivers side Kick - behind the emergency break... only place i can get the mic to stay put

I can't "help"...I'm not an SPL competitor......yet

But those equations don't make sense. They divide feet/second by viberations/second...and get a distance/second...ummmm Houston we have a problem.

Hell, for all I know those "equations" may make you the loudest muhfur in Texas...but they don't make mathematical sense.

Goodluck LBow.

[///M5 2,833]

But those equations don't make sense. They divide feet/second by viberations/second...and get a distance/second...ummmm Houston we have a problem.

You never cease to amaze me with your nonsensical babbling.

1131 Feet per sec/20 Feet = 1131/20 per sec or 56/sec or 56 hz Mathematically that portion is just fine. WTF are you talking about. I will save my issues with the rest of the article for later, but dopey you completely missed.

[mrray13 30]

everything i've ever heard says you want to tune below the resonant freq of your vehicle, I'd try something around 38-40hz and see how that works.

correct, and it varies per vehicle. most will say anywhere from 7 to 11 hz below peak.

LB, if you truely want to find your resonant frequency, seal up your ported box and burp it. start at 35 hz and moving up in 5 hz increments until it quits getting louder. say it got the loudest at 50hz. start at 45 hz now, and in 1hz go up until it peaks. then tune your box between 7-11hz below that peak. it'll take some testing to achieve that. build a box with a slot port (or aeros!!) that can be removed and modified to change tuning. start low as the port is longer. whole lot easier taking length off compared to adding it, lol.

and sean, i fixed your post, the double quote thingy you had going on confused the hell outa me, lol.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[Lord Baccus 1]

But those equations don't make sense. They divide feet/second by viberations/second...and get a distance/second...ummmm Houston we have a problem.

You never cease to amaze me with your nonsensical babbling.

1131 Feet per sec/20 Feet = 1131/20 per sec or 56/sec or 56 hz Mathematically that portion is just fine. WTF are you talking about. I will save my issues with the rest of the article for later, but dopey you completely missed.

do you know if im correct ? with 7' from the subs to the mic

7x4=28

28/1131=40.39Hz

so tuneing rufflly 10Hz down puts me @ 30.39Hz

do i need to do any additional math to account for the port fireing 90degrees out of faze ?

the subs fire forward & the ports (2) 6" Presision Areo's fireing up along the back window line, in an Old Ford F-150 X-Cab

i put the mic on the Drivers side Kick behind the emergency break.

Edited June 27, 2007 by Lord Baccus

[mrray13 30]

while i can't answer your mathmatical question, sean or someone smarter then me will have to, what i can say is this. what happens on paper doesn't happen in car. that simple equation doesn't account for everything in that wave's path, ie: your seats, your dash and anything else between those subs and that mic. hell, even the ebrake pedal is going to casuse deflection. enough to matter? i don't honestly know, but i'd wager yeah.

simply put, if it was just as simple as doing the math and porting to suit, the records we have now would have been accomplished oh so long ago. but it's not that simple, again, waaaaaay too many varibles.

IMO, the only way to do it, test. test and test some more. the very best i know follow the procedure, or a version of it, that i outlined above. they all hold/or have held world titles in dbdrag, usaci and meca.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[mrogowski 6]

correct, and it varies per vehicle. most will say anywhere from 7 to 11 hz below peak.

LB, if you truely want to find your resonant frequency, seal up your ported box and burp it. start at 35 hz and moving up in 5 hz increments until it quits getting louder. say it got the loudest at 50hz. start at 45 hz now, and in 1hz go up until it peaks. then tune your box between 7-11hz below that peak. it'll take some testing to achieve that. build a box with a slot port (or aeros!!) that can be removed and modified to change tuning. start low as the port is longer. whole lot easier taking length off compared to adding it, lol.

and sean, i fixed your post, the double quote thingy you had going on confused the hell outa me, lol.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

The bolded part is interesting. Kent, why would you want to tune below the peak frequency? To me, it would make sense to set your tuning *at* the peak your car resonates at. This way, not only are you getting maximum output from your port, you are also getting added volume from a resonating car.

Correct me if I'm wrong here...

[Aaron Clinton 2,372]

Whats the res freq of my house?

[mrray13 30]

you tune below peak, so that the box will peak at the car's frequency. if you tune at frequency, the box will peak above the car, and you'll lose output. you've got to account for the car's transiant response, if that's the correct term here. and the fact (and i'm not sure why) that a box never peaks at it's tuning frequancy, but always higher.

hopefully, someone with a bit more physics knowledge can come in here adn break it down correctly.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[mrogowski 6]

you tune below peak, so that the box will peak at the car's frequency. if you tune at frequency, the box will peak above the car, and you'll lose output. you've got to account for the car's transiant response, if that's the correct term here. and the fact (and i'm not sure why) that a box never peaks at it's tuning frequancy, but always higher.

hopefully, someone with a bit more physics knowledge can come in here adn break it down correctly.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

No need for physics, just some experience. Ok, so just to get things straight, its not the output of the port you are interested in but the resonant frequency of the box itself, correct?