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Old 08-28-2011, 11:41 PM
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Default setup for finding resonant frequency

the other day i put together a system to find the resonant frequency of various vehicals. it's a 1.1cf box with a 10" punch hx2 rfd2110 and a ~200w punch 2-ch amp. after displacement the box is 1cf, the sub only has 1 working 2 ohm coil and the amp stays at full pass. i have a 12v power supply and an oscilloscope at my house so i set the amp so it would'nt clip using a 60hz sine wave. i also checked the output voltage with my fluke 112 rms multimeter. i got ~18vac @60hz no clipping, i'll use that for a refrence later. i made it so i can clip the amp's power wire to the cars battery and i use my phone for the input. the bad part is the 1/2 blown subwoofer, it's a 2-ch amp so i can only use
1-ch of the amp with the single 2 ohm coil. i took it outside, set my term-lab mic about a foot of so in front of the sub and measured every frequency from 25hz to 65hz and averaged around 115db. i have 4 vehicals so i did test in evry one of them and got various results. oh yea according to an enclosure program the sub & box should have a Q of .76.

but i have a few questions.
would it be better if my setup was louder than 115db overall?
a friend of mine has a kicker comp 10 for sale but when i plug the specs into th software it says i will Q .5 with my 1.1cf box. should i wait for another sub that will have a Q of .7?
is there any way to improve my testing method?

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Old 08-28-2011, 11:48 PM
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The setup doesnt matter too much - You just need the difference between the anechoic response and the in-vehicle response.

Resonance may change some as higher power levels are applied because the vehicle effectively becomes more lossy, and less rigid as the pressure takes its toll. At this point, you may see your resonant frequency drop slightly.

Its a good, but basic setup. Later perhaps you can set one up to test sub/port orientation on the fly without needing to find the exact differences between the separate port and driver responses.
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Old 08-28-2011, 11:59 PM
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Well, if you know you have a Q of .7, you don't need the anechoic response, but personally I would still test it.

What (most) people don't realize is that you're not really looking for resonance, but rather cabin gain. Well, for SPL purposes anyway. You want to find the frequency at which you seee the most gain over your baseline (anechoic) with your in-vehicle testing.

For example... I did this with a 1cf and single 10 just like you, but I didn't know the Q. I tested in vehicle first and found that 37hz was the loudest freq at my given volume. BUT, after testing outside the vehicle, I found that my largest cabin gain was at 43hz.

It's a handy tool and useful knowledge, but so many other variables come into play to squeeze thenths out that a lot of that may go by the wayside when you get into full tilt testing. For instance, the size of the enclosure may skew the resonant freq by a couple hz or more. And that's just one of about 1,000 variables. Lol.
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Old 08-29-2011, 12:37 AM
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i asked about it being louder because when i measure my system in my car with my term-lab i get a very consistant reading (~1/10db) on any given day, that's at ~150db @ 45hz. with this new setup i built the max i have gotten so far is 119db. i mean when i shut the door i get around 125db (the actual sound of the door shutting), i noticed my neighbor playing music while washing his car and the meter was picking that up in my car. he doesn't have anything loud (factory), and i think it was also picking up other various noises. so i was thinking that if i had it louder it would almost for sure dround out any other noises and give me a more accurate reading.
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Old 08-29-2011, 12:39 AM
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taylorfade

how did you manage 157.5db with 600 watts?
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Old 08-29-2011, 12:44 AM
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Quote:
Originally Posted by bdgf2004 View Post
taylorfade

how did you manage 157.5db with 600 watts?
Hehe. Actually "500w"

Did you have your TL laptop plugged in during your testing? That will throw numbers around even when there is no sound. I was testing one day while my neighbor was cutting his grass. I thought I was picking that up but it was just "noise" from the AC outlet. It's not an actual decibel reading. It'll do it in a dead quiet environment.
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Old 08-29-2011, 12:46 AM
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no, i have never had it plugged in during testing.
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Old 08-29-2011, 12:50 AM
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What setting are you in? Mine doesn't even register until 120db in "SPL" mode. There is no way you shoud be picking up your neighbor's factory system. Lol. Try another cable.
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Old 08-29-2011, 12:58 AM
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i bought it new and have only used it abut 10 times. in spl mode it will allways flash around 107-109db. it is definately picking up my setup below 120db. i can play a frequency and it will display that exact frequency on my labto, and like i said the highest i've gotten was ~119db. i just think if it were louder i would be better.

i like your 5 gallon bucket. a while back i was asking for some suggestions for my dp 21's and someone recommended something similar to that.... i shoulda went with that!
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Old 08-29-2011, 01:16 AM
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Lol. 21" tooooobz!!! Do it.

IIRC, my setup was around 120db and it gave me pretty accurate and consistent results. I mean, it probably wouldn't accurately determine the best frequency for a wall or similarly huge build, but for every day "typical" systems where the build isn't drastically changing the listening environment, it'll tell you what you want to know.
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