How to find your vehicle's resonant frequency for noobies 101

[brad4021]

thanks for the write up!

[CLNFREAK]

some thing to make it easier when testing alone and sitting in the car ...

use a wireless mouse and set laptop up right out side driver window (make sure you can get out and in ) ... you can reset the TL with out getting out and dont need to have laptop in car vibrating the HD to death ..

[Aaron Tuck TBA]

This is exactly what is was looking for. I'm planning a wall in my 91 gmc x-cab 1500 and wanted to learn where to begin with RF. Thanks fellas really love this site.

[TaylorFade]

The method you've outlined is only accurate if the 10" sub in the 1cf box has a perfect 'Q' of .707. Otherwise... you're just finding that box's peak SPL in your car since the FR won't be smooth.

If you don't have a 'Q' of .707, you need to do the same measurements anechoic (outside the car) and compare the two results to find the largest deparity.

For example... you run the sweep in the car and it says the max SPL was 130db @ 35hz. But the anechoic measurement was also 130db @ 35hz. You are getting ZERO cabin gain there. But the box did 127db @ 40hz anechoic and 129db in the car. You're getting +2db of cabin gain at 40hz.

40hz will crush 35hz in that car.

[Aaron Tuck TBA]

how would i perform the test outside the car?

[TaylorFade]

how would i perform the test outside the car?

Just find a spot as far away from walls ans stuff as you can. Ideally, you'd want to suspend the box up in the air 6 or 8 feet, but that's getting a little crazy.

Put the mic a couple feet away from the sub and do the tones. Record the SPL for each tone. Do the same in the car. Compare the two results and the largest difference is where you're getting the most cabin gain.

The sweep is super easy if you know the box is perfect. But if not, you need to record each frequency. It's two pages of notes and about 30 minutes to do it right.

And as someone else metioned... a 1cf box is a far cry from what most of us will have in the car to utilize that resonance. But.... it's better than nothing.

Murphy swears you can fire up the termlab and just ride down the road with it. He supposes that the resonant frequency will just "show up" on the TL. I've yet to test his theory.

Also... a quick and dirty way to figure it without a TL is to just measure the distance from the back of your sub, then to the port, then to the mic spot and find the quarter, half or full wave.

For example... say my rear wave has to travel a total of 20 feet from the sub, out of the port and all the way to the dash. Speed of sound is ~ 1130 feet per second. 1130 divided by 20 feet is 56 (full wave). You're likely to have some really nice cabin gain at 56hz.

Edit... speed of sound is 1116 feet per second. But you get the idea.

[Aaron Tuck TBA]

Thank you so much for the help will be doing this as soon as i get a TL.