Originally Posted by
Empire
radio shack sells one... don't know how awesome it is gonna be considering it is pretty hard to maintain a set tone, as that is what you are measuring with decibels... basically, how much distance a certain tone/note can carry before loosing its integrity.... get a trumpet and play a B flat... after a certain distance, it is no longer a B flat... that distance is your decibel rating...
That's hilarious. And wrong.
You're getting the doppler effect mixed up with sound intensity. Google both of those. dB in this case is a ratio of pressure levels. It has nothing to do with frequency changes, apparent or otherwise.
The meter from Radio Shack will work fine. The problem is that while you may be under 79dBA at 50ft, there is no way in hell that your exhaust is quieter than stock. I once walked by the muffler on my stock KA S14 on a lift at idle, raised up to ear level. The ambient noise of the shop was such that I couldn't even tell the car was running at a distance of less than 1ft. That is, until I felt it blowing on my face.