posted
I am relatively new to porting and have only done it to say 30Hz, 35Hz, and so on. But say the resonant frequency of my ride was for arguement 58Hz, where would I port the box to for max SPL? Should it be ported right to the resonant frequency, or below. If below, how much?
And one more thing, I am planning on making a box shaped like this __ |..|X |./ |.\ |__|X
and placing the ports where the X's are. I have been hearing a lot of talk about not being too close to the box walls, but this will be pretty close, see any problems. Why is it bad to have the vents close to the box wall in the first place?
And lastly, does porting like that in a V really change the tuning of the box?
posted
WoW. That looks like my box. I do plan on using them 45deg PVC piceises to get the port inlet away from the walls. I have two Vega 10's on the top and two vega 10's on the boton with a divider down the midle and each sub in it's own enclosure. I haven't heared it yet though because I been working The box is done and by this weekend I will have the power hooked up will let you all know what happens. And for all of you how followd my thead with me putinng a sys in my girlfriends car I will be able to tell you if her 4 Vega 10's in the ported box blows away my 8 Vega 10's in my seald box.
posted
I was planning on useing vents instead of regualar ports. capple, what are you talking about with the 45degree PVC? And anyone who knows where a box should be ported to still feel free to answer(Dukk?)
posted
Well in them other theads you seen we where talking about using a elbo to get the mouth of the port away from the wall of teh box. If you are using vents here is some great info from a nother fourm posted by audioextreme...
quote:The cross-sectional area should be the same as that prescribed for a round port. In your case the round port is 3 inches. So you would need a rectangle that has 7.069 sq inches of area. The ratio of the two sides of the port should not be any more than roughly 9 to 1 to prevent tuning shifts introduced by excessive friction between the rapidly moving air and the port's surface. It is just a rule of thumb.
For duct porting where you have a lets say 90 degree angle to get the port to fit the physical length of the port is measured down the dead center of the port from end to end.
If one side of your port is a wall of the box add an end correction factor. Because one wall of the port is also one wall of the enclosure and this wall extends beyond the end of the port this adds length to the port. To calculate end correction factor, add one-half of the width of the port (from the inside of the port on the box wall, to the side of the port in the center of the box) to the physical length you calculated for the port length. or in your case the manufacturer spec.
lots of good stuff in ther the rest of teh thread is in the (Subs and Enclosures) fourm and the thead is called (Port Design and Tuning)
posted
audioextremes thing helps me out with another thing, since I was planning on using one wall as a vent side. Tell me if I understand it right. lets say I have a vent 6" long and 4" wide, I divide the width by two, then add it to what, the lengh(depth) of the port, or to the 6" length?
And how close is "close" to the side of a box? Say with a 5" wide vent, would 2" be sufficient if I don't use the side as part of the vent?
Dukk, still waiting for you to answer my other question...
------------------ Adolescent Sound Disorder
[This message has been edited by ASD (edited 06-29-99).]
posted
I'm not sure how to use this formula realy. I enterpit it as using 1/2 the with as the with from teh wall the port is using to the opposit side. So your vent is 6" deep by 4" wide by ??? tall. I thing you use the ??? tall and divid by 1/2 and then yes add it to the overall lenth. I don't know if he has see this but you may want to try to e-mail hi to get details if he dosn't respond soon.
posted
Thanks! That helps. If the port doesn't use the box wall as a side, how close does it have to be to use that formula?
And back to the origional question, say the resonant frequency of my car was 58Hz, where would I tune the box to for max SPL. C'mon, I know someone know the answer with all the bass-heads on here...
posted
Pitchers are worth at thousand words!!!!!! I think that is what I said. Tuning frequency. I know I see this talked about in this forum. Where though??? If I remember right someone said. To tune around 35hz. The tuning freq. is the point with the most out put of the port with the lease amount of movement from the woofer. I will look for that thread and post if I find it.
posted
Found it right in this forum. I seem to do this allot but all must appreciate me quoting the person so here is what Dukk wrote:
quote:If you are thinking that a box has it's most output at the tuning frequency, it doesn't. At tuning point the port has maximum output but the woofer has minimum movement so it really isn't the ideal. This is not to say that proper tuning won't enhance SPL at a certain frequency. Tuning in the 40Hz range usually produces strongest output in the 65-85Hz region - the exact place you want it for SPL.
So I was a bit off but even at that if a guy has accesses to this info all the time how need to retain it all word for word. A guy reads allot if you visit this place often.
posted
OK, now that I've pretty much gotten all my questions answered, one more. How close to the side of the box does the port have to be to take into effect the end-correction factor? What % of the width of the port, or just how many inches? Thanks for all you help!
posted
If the port is 1/2 the diamator away from the wall your doing ok.
audioextreme posted
quote:......If the ports are farther than half the distance of the diameter of the port away from the wall forget it. Example, say a 3 inch port more than 1.5 inches away from the wall.
If your ports need to be real close to the wall because of placement problems. You can use elbows and such to bend your port. Just remember mesure down the center.
An easy solution is to make your way to a JL Dealer and get some flex port. If you use them you can squeeze ports almost anywhere.
posted
Boy you don't show up for a couple days and......
Right on it all! The tuning should be around a half octave below the resonant frequency. This is solely my own finding and is supported by nothing other than my own experience... Actually, more technically, I have found that the greatest output of a ported box is usually a half octave above tuning.
In your vent example: If your theoretical vent is 4" wide (ie, the side of the vent opposite the wall is 4" away from it) then the vent should be cut 2" shorter than design length. This way the length of the vent doen the center line will be as design with the 2 extra inches factored in by the 'shadow' of the wall. I'm merely trying to clarify what has already been said.
Lastly, no, the shape of the V should not affect tuning.
------------------
And that's the bottom line, cuz: LORD DUKK SAYS SO!
The Big Show The Dukk says: Know your bass: PORT your damn box!! Have HoleSaw, Will Travel!
posted
"Actually, more technically, I have found that the greatest output of a ported box is usually a half octave above tuning." So, Dukk, what you are saying about the tuning/output thing is that in your findings, if you want a box to be the loudest at 70 hz(at least without figuring in cabin gains and all of that good stuff), you would port it to about 52? Did I figure that right?
posted
The same questions seem to come around every so often. Sometime in different way but always the same answers. I and I'm sure other don' mined pulling up you slack a bit every so often Dukk. Even though you came up with great advice three weeks ago I recognized it and now I know I must be retaining some of this great knolage.
posted
Basically a frequency ration of 2 is an octave. X2 or /2... The long ill deff uncensored definition: The interval between two sounds having a basic frequency ratio of two-or, by extension, the interval between any two frequencies having a ratio of 2:1. The interval, in octaves, between any two frequencies is the logarithm to the base 2 (or 3.322 times the logarithm to the base 10) of the frequency ratio.
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