posted
I was just thinking of changing my 140sq" rect port to three round ones and firing them through the rear deck. I noticed that if I use 3 8" diameter ports which gives me 150.7sq" and use Winisd to calculate the port length it is different than if I just punch in 150.7sq" rect port?????????? WTF Is the "use the same area rule" an estimate or a fact? How else would they calculate it in winisd. Could somebody please try this on leap software and see what they get.
My car has a peak around 62-63Hz. And If I tune to 45Hz I get a nice 4th order chebychev response with a few dB of ripple and -3dB's at 40 and 70Hz at the dash. So I want to keep this if I redo the ports. But I want to be able to open up the third port to increase the tuning freq to 62-63 so that I get a high Q peak at 62-63Hz if I want to compete.
BTW because my box is so big compared to the Vas of the speakers, My peak response is right at the minimum impedance of the speaker system (The tuning frequency). I think this is the secret behind DD's. Put them in a big enough box, you get minimum impedance, max output, max port output, minimum cone displacement and maximum power handling all at the same frequency. How beautiful is that. Those are usually spread out at different frequencies.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
It is right, but often overlooked. It takes account of the effect of extra friction. read the JL tutorial section on ports and it goes through this in a lot of detail. Colin
------------------ Spy Shots Bass: Sitting IN a port while playing a 30Hz test tone flat out. See also: Fun; Insane.
posted
yeah, port area is not a good tool whatsoever in finding port length. When you consider the use of slot ports versus round port, the volume/area is not constant.
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Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
http://tools.autoaudio.com uses the JL formula. I use that rather than working things out by hand. Don't much rate the box performance modelling software though. L-pad calculators are good. Colin
------------------ Spy Shots Bass: Sitting IN a port while playing a 30Hz test tone flat out. See also: Fun; Insane.
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