Finding Peak Frequency (you are kicking my butt here, acoustics)

[SnowDrifter]

I've always read that you take a sub in a sealed box and play a sweep. What am I looking for? The highest reading on the termlab?

How much of a chance is there that there would be some other harmonics that might give be a false reading?

Right now, all I have is a kenwood kfc-xw800f (dinky little 8" woofer) and a bassworx prefab that would be .5cuft sealed if I plugged the port, which would be the spec for the sub.

Would that be acceptable to use? Does it make a difference as long as the termlab can pick it up?

I also have an IM-SG and a ac/dc clamp at my disposal if those could find a use

[SnowDrifter]

My 12s are in a 4cuft box and to measure my peak, I sealed the end of the port with some wood to make it a sealed box and turned my SSF all the way down, and my high pass all the way up. Then I played a 20-80hz sweep

The highest termlab reading was at 49hz.

But when I pulled my woofers to make some box changes, I decided to measure the t/s just for fun. And the Fs of the sub was also 49hz. And the Vas was .47 cuft.

So I'm wondering if I may have gotten a false reading because that's what my sub's Fs was or is it just some strange coincidence?

Also: my peak didn't change whether I put the meter at the dash - sealed, headrest - sealed, or headrest - 1/2 windows down

[Colin - STAPUFT]

Crazy that the readings would be the same on the TL in every place you tested it...

There is all kinds of math you can do to get the mathmatical theoretical resonant frequency of your ride, but... it just gets you in the ball park. The only real way IMO is to actually test it with a TL. If I had access to a TL, that would be all I would use to find what you are loudest at. All kinds of stuff can make the frequency change a bit- weather, temperature, moisture, etc... as the air will get thicker and heavier under some conditions and thinner and lighter under another... but honestly- I don't think it will make any real appreciable difference.

I think that the 49 hz thing is just a coincidence. But are you sure the Fs on your subs is 49 hz? That seems really high to me. Is that on the 8s or the 12s? Most of the time Fs is somewhere around 35-25 hz for a 12 (depending on what the sub is for- spl, sq, sql).

[mrd6]

Chris, just think about it this way. You want to create as flat as a response from an enclosure as possible in a free air environment so that you can then put that flat response in your car and see which frequency is the loudest. That frequency is theoretically your in vehicle peak or resonance. In general people say put a 10 or 12 in a sealed enclosure and test because that is more likely to have flat response than any ported or larger cone area enclosure.

Another thing to keep in mind when you try to find your enclosures peak frequency is that you need to block off your port on the inside so that the port volume is not included in the sealed section.

[STEALTH808]

find impedance peak...

[mrd6]

Also, I have an extra lvl 3 12 sitting around if you decide you want to use it to find in car peak, just let me know. It should play flatter than the crossfires in a sealed box

[SnowDrifter]

I think I got it figured out. Borrowed a friends kicker comp and sealed box and got a bunch of different peak numbers depending on the position of the meter or whether the windows were up or down. Some numbers were lower, others were higher