dB drag music

at0m · Post by **at0m** » Sat Apr 20, 2002 10:14 am

Hi,

A workmate has his car tuned and he's put a mega hifi in it. He's in a tuning club, they do demonstrations, ralleys and dB drags. In a dB drag, the one with the most dB in his car is the winner.

Has anyone experience with the CD's they use for that? As they seem very expensive, he asked me to do a simple tune to test his installation.

So now I have a couple of questions/remarks.
-> I guess they measure the dB in peak value?
-> How can I create the highest dB peaks in his sub woofer? Should I read the info on the sub, about it's frequency response etc.? How should I interpret it?
-> Any particular synthesis I should prefer over another?

I'm Manuel form Barcelona and I know nothing. Anyone experience with this or can someone explain me how to get him the highest possible dB with his setup?

Yes, not all people enjoy music the same way we do

edit
Hi Paul,

I'm still thinking of a creative way to spend my 1000th post. Not easy, I'll have only one. Becoming Guru then will be to much for me. I hope people realise it's the amount of posts which makes the Guru, it's only a vague reflection of the real contributions. I do not consider myself Guru at all, I just like to bring up idea's and learn myself.

Ken,

The mic is placed inside the car, in the center against the windscreen. He says he'd only use his sub (which is in the trunk). You point out a good reason for him to leave his mids and tweeters on: higher frequency, higher dB. Wasn't it low freq's producing more energy? Or is that in db(A)? I'll have to check what a dB meter measures. I know the cops use dB(A) here.
Also, you confirmed my idea of using sine waves. Hey but if you clip those, what kind of clips do you suggest? Clipping like in reaching 'more than 0dB' or clipping like 'inverting the signal when on max amplitude'. Both signals will produce about the same audible clip, although +0dB clip may eventually make a square of the sine.

Subhuman,

Thanks for the link!

atom.

[ This Message was edited by: at0mic on 2002-04-20 19:59 ]

[ This Message was edited by: at0mic on 2002-04-21 05:16 ]

paulrmartin · Post by **paulrmartin** » Sat Apr 20, 2002 11:19 am

For your 1000th post Please explain to me how you are not in Belgium anymore... And that you know nothing????

[ This Message was edited by: paulrmartin on 2002-04-20 12:20 ]

kensuguro · Post by **kensuguro** » Sat Apr 20, 2002 2:06 pm

I've had a drink, and I'm pretty tired at 6:30 in the morning, and I'm not experienced at all in this field.. I'm just hypothesizing from my scientific knowlege about sound... but my guess is that if it's dB, as in the general amount of energy included in a given sound.. I'd say go for higher frequency. The higher the sound, the faster the velocity, the shorter the wavelength, the more engergy the wave has. (imagine ultrasonic sounds can cut rocks) The machines they use to measure the dB would probably be sensitive in this way. Also, even if the dB were to bo measured with ear and body, you need much more bass to reach the same amount of impact as the higher frequencies.

BUT, if they are going to use a mic+measurement device combo that is at a certain distance away from the car, then you'd want to go for bass because it has better spreading ability. It even wraps around obstacles too. Make sure you use Celmo's subbass or some sort of similar device.

The best would be to use a bunch of pure sin waves because they have the best ability to pack all the energy into a single wave. Also, make sure you have each of the sounds last long enough so as to leave enought time for the wave to reach the microphone. (please do a "speed of sound*1/distance from car to mic" calculation)

If you ask me, the best you can do is to have a 22050hz tone(if working at 44.1khz), at max amplitude shoot straight at the measurement mic. That will give the highest energy burst. Better yet, use a higher sampling rate and shoot a sin wave right at the nyquest value(sample rate/2) for even more energy.

Just remember, high=more energy but have to be more accurately aimed.. low=lower energy but can "slip by" obstacles. Whatever you do, keep away from white noise because it has same energy level in all freq range, which means it's weak in any particular frequency (which is the peak). The best would be to find which frequency your friend's speaker can output the best, and then have a sin wave right at that frequency. Because unless his speaker's are studio monitors, it'll have "sweetspot" frequencies.

Actually, now that I think about it, you may even want to totally clip the material. I say this because, if you clip, you cause higher harmonics an still keep the max output. And higher harmonics means even more energy, so you gain energy, even if you don't increase the volume. I think that should raise the dB count a little. Usually, in a digital environment, clipping won't increase dB but in a real acoustic environment, the natural resonating and such might make the sound actually louder. Dunno, you'll have to experiment.

Also, another factor you have to keep in mind is that depending on the distance, you might have phase cancelation.. you'd want to keep that to a minimal.. so it's wise to keep your mixes pure mono.. Also, it's easier to tell for lower frequencies where the phase cancellations are occuring, so it might be easier to base your mix around bass. And since phase cancellations also occur naturally, at one point in your song, you might want to do a 0-180 degree sweep, preferable when it's reached it's highest energy, just so that you can make sure that the measurement mic has recieved all possible phase positions during the highe energy phase of the tune.

Oh well, maybe these info can be useful.. maybe a bit to theortical. I hope you and your friend can kick some serious arse.. these are my 2.. or maybe 3 cents. Good luck!

borg · Post by **borg** » Sat Apr 20, 2002 3:43 pm

i read something about boom car music a few years ago. the article featured a record label specialized in music designed for these cars. i think the name was 'oil records'. i'm not sure though.

subhuman · Post by **subhuman** » Sat Apr 20, 2002 3:53 pm

Check this out

http://www.termpro.com/dbdrag/magazine/9704/tips1.html

algorhythm · Post by **algorhythm** » Sun Apr 21, 2002 12:15 am

- some of my friends do dB drag. Actually, around here the contest is maximum SPL, and they take the measurement in the center of the car right in front of the windshield, with contestants standing outside using a remote.

They asked me to make them a CD for this, but I never bothered. Maybe I will now. Basically, the CD's I have heard are short bursts of sine wave ~ all really low frequency. Usually, it is a sexy woman who says "30Hz" and then a 30Hz sine tone blasts. Then "31Hz" and a 31Hz sine tone blasts . . . .