banginAltima Posted July 29, 2009 Report Posted July 29, 2009 do you have to use of a Term Lab or Ac meter? If you build it, db's will come... NSPL World Record Holder Trunk 0-1800 watts---147.9 with 1722 clamped watts @ 40Hz(9-20-09). Competition Only Record Holder Trunk 0-500 watts---148.1 2006 Nissan Altima 3.5 SE Currently Rebuilding.... My 150db Plus Trunk Build I do box designs. [benH] 6:24 pm: clipping doesn't really hurt subs [benH] 6:24 pm: being an idiot is what blows subs
Ben Building Posted July 29, 2009 Report Posted July 29, 2009 You do not need a TL; just a Radio Shack cheapo db meter a reference sub system (just a sub with a reasonably flat frequency response), and some time. The cheap meter only reads up to about 130db or so, but you're not going for max numbers here, so the volume will be low. Play test tones through your reference sub, starting at 20hz. Write down the spl at each frequency and you should notice a trend. Your reference sub will probably be the loudest at the car's resonant frequency, but not always. You will need to measure your reference sub's output in free-field just so you know it's response characteristics.
Boon Posted July 30, 2009 Report Posted July 30, 2009 Your peak shifts several hz as db increases. The only way to really find it out is with a lot of time, a hacksaw and a termlab. 10.x volts fo' life!
Ben Building Posted July 30, 2009 Report Posted July 30, 2009 Your peak shifts several hz as db increases. The only way to really find it out is with a lot of time, a hacksaw and a termlab. Boon is correct. Vehicle resonance changes with the pressure level. This is because a large force pushing against the car demands the car push back with an equal (larger) force. Resonance, however, is a function of mass and damping. Although, due to deformation, the metal's damping factor will change the more you push it, it will generally still stay in the same ballpark. I believe that you do not need to purchase the TL because the RS db meter will get you 95% of the work for about 1/15th the cost. Unless, of course, you are heavily into competition and cant afford to waste a tenth.... Boon, do you agree?
Boon Posted July 30, 2009 Report Posted July 30, 2009 Indeed The thing is, the only people that will really care about the Fs of their vehicle are the people who are competing. IMO there's no point building to the Fs if you're going to play music. The box, whatever you tune it to, probably won't peak at the same point as the vehicle, this is what takes the hours and the hacksaw. Which is why I argue that finding out your resonant frequency at 125dB is not entirely useful. 10.x volts fo' life!
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