resonate freq of a car

Just thought I would cut & paste this from a post I made on Direct techs foum. didn't see it here.

Long post, so here goes....

Make a sealed box, with a single 10 or 12. Measure how far from the mic the box will be in the car (let's assume 12ft) hook the box up OUTSIDE the car & place your mic 12ft away from the box. Do this outside, so not variations from the shop will effect it. Note each freq & dB measurement. This way, when inside the car you will know if the car is peaking or the box. Make sure to test the box at the same power level as when you are inside the car.

Now repeat the test with the box INSIDE the car, using all the same setup, just now the box is in the car. If you want DB Drag setup, make sure car is sealed, if USACi, make sure door or window is open.

make a chart with the readings at each freq & it's dB's...like this

freq in car out of car dfference
80Hz 150.0 125.0 25db
75Hz 151.0 126.0 25db
70Hz 155.5 126.0 29.5db
65Hz 156.5 135.5 21db
60Hz 153.9 127.9 26db
and so on, I kinda exaggerated (unless you have an old audiocontrol meter the readings will be a lot lower), but you can tell the CAR got louder at 70Hz, & the BOX got louder at 65Hz.....with that being the loudest reading, change your box so it is loudest at a diff. freq. try to make it as flat responce as possible (in this case I would make it larger to bring the res. freq. of the box down) then repeat BOTH tests. A good test range is 80Hz down to 30Hz. Also, as you get it tuned in go from 5dB increments to 1dB. Smaller vehicles tend to resonate at a higher freq. than larger. examples, 2000 tahoe around 35Hz & CRX 60Hz to 70Hz.....although the wall in my CRX was 52Hz

this takes a lot of time, but is worth it. This also only works for a stock or pro stock setup, a wall is a totally different can of worms.

This gets you in the ball park, but in no way is the be all end all of how to do it, just what I know others have used, & has worked for me. After this it's time to start building boxes that peak at the vehicles peak, trying different box locations, facing tifferent ways, & on & on & on

side note....some say measure from the box to the windsheild or back glass to windsheild (in feet) & divide by 1130 (speed of sound) to find the wavelength, & then divide by 4 to get the 1/4 wavelength...these people are wrong, it just dosen't work. As was stated, to many variables, maybe in a sound chamber perhaps for a super mod, but not in the real world.

For more info on this go to either dbdrags web site or usaci website (www.soundoff.org), & check their forums. Look for threads by either Steve Meade (west coast) or Robert Kollar (mid west), as both are kick ass guys, & loud as hell. The USACi test CD has all the tones you need also.

We are always hiring
1-88crx
2-PBX XS15's
4-Interfire IFD1000C's
155.8 USACi

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used to be loud, used to be fast...now I am married LOL

     you basically described how to measure the transfer function of your vehicle

Transfer Function? could you give me a definition of that. I have not herd the term.

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used to be loud, used to be fast...now I am married LOL

  transfer function is the effect your cars environment changes freefield measurements...due to hard reflections,soft reflections and so on....example: box outside vehicle ( freefield ) 65 hz- 100 db... same variables box ,sub , power. etc. but in car   65hz - 110 db....plus 10 db your cars natural frequency response has a 10 db boost at 65 hz. due to cars natural acoustical properties....you are correct in the manner you take to measure this ...  sorry to cut this conversation short but i hav got to go ...i have an old article on this subject in an old magazine 92 - 93 i tink written by richard clark  ...THE RICHARD CLARK. if i can find it i will elaborate more on this subject..

So with all this wisdom your spreading, does that mean your coming back into the lanes?

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2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR
2007 USACI World Champion
2007 World Record
2006 USACI Finals 2nd Place

    never been in the lanes but i would like to if circumstances allowed jeff

I remember the the delivery truck that Richard Clark...& I think Dave Navone? (not shure on Dave's involement...poor memory) with the 6ft tall sub.....one of the thinks back in the day that made me go WOW...lol still kinda does.

Not shure if the back in the lanes question was at me, but I MAY see if I can blow a 60 out of the crx (prostock, I had my wife take a hammer to the wall, I couldn't do it), using everyday type less expensive equipment. I no longer own Audio Expressions, so the main drive of our SPL team is gone, I would just be there for my own peice of mind (knowing I never got MY car to blow a 60 bugs me).

We do still have our supermod Camaro, but drive to finish it is lacking. I know how comsuming SPL gets, I'm not shure how far down that road I wanna go again....too many other interests in life.

Perhaps the title of the thread could be changes to res. freq./tranfer function, for those that do a search?

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used to be loud, used to be fast...now I am married LOL

  wow if you remember richard and navone ..that is when it all started for me ..i didnt know either who the question was referring to eithher  buut i am very curious of what i could do in the lanes i am pretty confident  my passion is tremendous but my finances are not what happened to your store ...i have th drive to finish ....annnd thhe wisdom.        you dont know how  far down the road u wanna go   i just wanna chance