Resonant Frequency

[biga48197]

ok I have a 2000 dodge grand caravan. I wanted to know how can I find the resonant frequency of my vehicle.. is there a formula, do I have to create something, what? I am open to all suggestions. Thank you in advance.

[Sniper]

Heres what you do, go to Realmofexcursion.com and download all of the pure tones under 150hz, put em on a disc or something or what ever you can use to play them, then cycle through them and find which frequency seems the loudest in the car to you.

[raytard]

while that does work, the scientific way to do it involves a driver in a sealed box, test tones from 20-150hz, and some sort of accurate microphone that allows you to measure volume per frequency and find where it peaks (ac mics are great for this, despite the fact everyone hates em for SPL, if youre just comparing volumes at different frequencies they're perfect)

depending on what you add to your car, it may raise tuning, like if you throw a 30 cube wall in there, the tuning is going to be raised a few hz, right now its probably somewhere in the high 30's/low 40's, but it may be even lower than that

[Boon]

As raytard said.

30-80hz sweep on a termlab is good as well. Put a plate over the port on your box - you can't just use a little box because the box's size and orientation can affect resonant frequency.

Unfortunately sealed is only going to give you a ballpark figure - the resonant frequency usually drops by a couple of hz as the pressure increases. The only real way to find it is to burp, wait for charge, bump the frequency by 1, burp, etc etc etc.

[tommyk90]

Actually, you both are only partially correct.

What you need to do is test a sealed box inside AND outside the vehicle. That way you find out the baseline peak for the enclosure itself. Put the db sensor a foot or two away from the speaker, then play 20 to 80 hz one frequency at a time and write down the SPL score

Then you take that enclosure, put it in the car, and run the same frequencies. Write down these scores as well.

Now what you'll do is subtract the ambient (outside) score at each frequency from the in-vehicle score at the same frequency.

The frequency with the largest difference is the vehicles resonant frequency.

Simple example

35 hz outside vehicle=115 db

35 hz inside vehicle=135 db

difference is 20 db

40 hz outside vehicle=117 db

40 hz inside vehicle=140 db

difference is 23 dB

In this VERY simple example, 40 hz would be the resonant frequency.

To sum it up, the resonant frequency is the frequency at which the vehicle itself will increase your dB level the most. Sorry if I didn't explain it simply enough. Even with this though, you still have to do LOTS of testing in the vehicle itself with different size/layout enclosures to find out the best combination. And by doing this your peak frequency may change.

The bottom line is that finding the resonant frequency will only get you so far.

Edited December 26, 2008 by tommyk90

[DHFHades]

the resonant frequencie of my car is like 64hz, so if I decide to compete do I need to tune my box to that?

[Decaf]

~6-10hz below resonant frequency, depends on driver

[bunkerking09]

Testing. It will take a lot of time on the meter to find what your EXACT resonant frequency is.And take a lot of wood for all the text boxes. I'll try and sum it up on how to do it.

Tune a box to say, 40hz. Run a sweep, see what it peaks at. Make another box tuned to differentlylets say 45, see what it peaks at. Measure your SPL everytime you do so. If it got louder with the second box, then that box is closer to your vehicles resonant frequency.

TEST TEST TEST

[DHFHades]

I ran a sweep and then went to tones, and from 55 to 60, 60 was noticably louder, and from 60 to 65, 65 was WAY louder, but then at 70 it dropped off pretty bad, so I was guessing it to be about 63-64 ish. but then I did the 1-30 hz sweep and my subs got REALLY hot...lol

[bunkerking09]

I ran a sweep and then went to tones, and from 55 to 60, 60 was noticably louder, and from 60 to 65, 65 was WAY louder, but then at 70 it dropped off pretty bad, so I was guessing it to be about 63-64 ish. but then I did the 1-30 hz sweep and my subs got REALLY hot...lol

so your vehicles resonant frequency is between 60-70 hz. Heres what you do

1. Build a box with aero ports, and tune it to 60.

2.Test @ 60hz, measure your spl

3. Cut ports to tune it to 61, give your batts time to recharge, AND DON'T CHANGE ANYTHING BETWEEN TESTS! Seats, box placement, batt charge, make sure it all the same every time.

4. Test @ 61 hz. If you measure louder than before, then you're getting closer.

5. Cut ports to tune it to 62 hz, charge her back up for another run.

6. Test again

Repeat this process until you drop on the meter, then you know that the last one you did was your peak

hope that helps. I think there should be a sticky on this.