posted
can someone tell me the equation for figuring out your cars resonsnt freq. not the box resonant freq.??? i believe its the 1/4 wave calculation...
i have searched for it and not been able to find it!!!!
posted
a crude calculation can be done buy measuring the total length of the inside and working out what wavelenght that corresponds to! basically you can use a quarter,half etc of that freq.
i might be a bit vage but im pretty much retarded when it comes to complicated maths i used the principal on my extreme car with succcess but i just kept punching numbers into my calculator till they looked right
-------------------- _ _____________ _ *on 2004 rules - *australian extreme 1 record holder!* *Owner and builder of australia's loudest extreme spl car* 1 Digital Designs 9915 + 4 concept d2400a's -"160.9" on new termpro meter Posts: 37 | From: western australia, | Registered: Jul 2002
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posted
The reason why 1/4 wave theory is important is beacuse the highest point in a freq. is at 90 deg. of phase.Also the fact that a 60hz sine wave is about 18ft long.So we use the 1/4 wave theroy at its peak at the mic.The calculation is 1130 divided by the length of distance in feet from your speaker to the mic placement.Then divide by 4 and that will give the number in cycles per second (hz)at 1/4 of the wave.1130 beacuse sound travels at 1130ft per second at sea level.Im sure the speed my be accerated if you were in like the colorado 10,000ft about sea level so you might wanna take that into account.1130/distance from speaker to mic/4.Now thats the easy part if working with a ported box.Now if youve have a ported wall and the sound/air coming out of the vent is 180 deg. out of phase it would cancel the speaker wave.The trick is to aling the back wave with the front wave at mic placement.Which I would like to get some info on myself.If you need more info do a search on 1/4 wave theroy and theres quite a bit of info.
posted
Sorry Im not sure of that fact.You might try a search on the net somewhere under speed of sound and acceration.I know it will make a diffrence up there in colorado since thats where the long drive contest for golfers are in denver.Golflers that drive a ball 350 yards here in dallas can drive 450 in denver.If i had to guess it would be somewhere in the 1700-2000ft/second.But thats just pulling a number outta my ass.Good luck.
i know i loose spl at this altitude i would like to know how much but i guess ill figure it out someday...
in the next 2 weekends i have to spl shows to go to and one is at about 5000 and the other is about 7000 so hopefully that will help me figure it out...
posted
The one problem with that is that your car is NOT a perfectly elastic enclosure unlike a MDF box. So to that end, the 1/4 wave won't work.
According to the 1/4 wave theory, I should have a peak at 32hz and again somwhere at 60hz (forgotten the exact number) and you know what my loudest note has ALWAYS been? 42-47hz and that was pending box design.
the 1/4 wave theory doesnt work, nor even give you a good idea. The best thing you can do however is to mate the best sized and built box for your sub's compliance and power applied and build it to interact as well as possible to your interior.
-------------------- 2005 Florida Street C Champion 2004 SBN Street C Champion 2004 SBN IDBL No Wall Champion 2003 NOPI Nats Street B Champion
quote:Originally posted by Bumpin' Yota: The one problem with that is that your car is NOT a perfectly elastic enclosure unlike a MDF box. So to that end, the 1/4 wave won't work.
According to the 1/4 wave theory, I should have a peak at 32hz and again somwhere at 60hz (forgotten the exact number) and you know what my loudest note has ALWAYS been? 42-47hz and that was pending box design.
the 1/4 wave theory doesnt work, nor even give you a good idea. The best thing you can do however is to mate the best sized and built box for your sub's compliance and power applied and build it to interact as well as possible to your interior.
Hey, You are a pretty smart fella!
-------------------- T3 Audio Incorporated >World Class Subwoofer & Speaker & Amplifier Development< Johnathan Demuth
"All our dreams can come true, if we have the courage to pursue them."-- Walt Disney
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