Estimating Exhaust Sound Levels

[Cp1]

umm i just bought a scosche DB meter from radioshack (about $50.00) and so far its been dead on accurate... why guestimate when you can know for so little or i dont fully understand the point of this thread.

[vex]

Originally Posted by Cp1

umm i just bought a scosche DB meter from radioshack (about $50.00) and so far its been dead on accurate... why guestimate when you can know for so little or i dont fully understand the point of this thread.

You should see the other similarly named thread. Just out of curiosity how do you know it's accurate? Do you know the %error of the device or does it come with a certificate of accuracy?

This thread is about estimating sound levels before purchasing a component for use. IE: Depending on what muffler or combination of mufflers you're looking at you can estimate a reduction in the DB level to be 10, 20, 30, or 50% given the organization and orientation of the mufflers.

So say for example a simple estimation tool was developed for perforated tube type mufflers based on offset as well as pipe diameter and filling material we could say the following:

Straight through 3in Diameter PT muffler with Stainless Steel packing will reduce the intake DB levels by 12%
A single 3in D PT inlet with a dual 2.5in D PT outlet with Stainless Steel packing will reduce the intake DB levels by 15% per outlet
A single 2.5in D PT muffler with offset inlet outlet with stainless steel packing will reduce the intake DB levels by 17%

This means we could do a mathematical estimation of the exhaust DB level by the following:
100*.88*.85*.83=62.084
Which means there would be a total DB reduction of 37.916%

This means if you have an engine putting out 120 DB at the loudest RPM you would hear 74.5008 DB out the tail pipe.

Unfortunately exhaust noise simulation is still fairly hard to setup in a CFD like program. What we can do however to make things easier is record the exhaust DB levels (accuracy is less important when just getting a statistical distribution of the sound) by means of DB meters. Once we know the individuals components reduction in noise (IE how much a single muffler quiets the noise) and put the component on the exhaust system to record the system wide reduction in noise we can postulate or project the probable decrease in noise to similar setups.

I'll edit this post with the link to the other thread concerning this.

Edit:
http://www.rotarycarclub.com/rotary_...ad.php?t=11969