Estimating Exhaust Sound Levels

[NoDOHC]

The attenuation of the sound amplitude occurs naturally in free air.

The sound energy measurement must take place at a specific distance from the source.

A good multi-chambered (perforated pipe-type) muffler is about 30 dB. A high-performance (straight-through) muffler runs between 7 and 15 dB. A straight exhaust is about 5 dB. A presilencer is frequency-dependent attenuation (typically between 5 dB and 20 dB depending on engine speed) they are typically high-pass filters. Actually a straight exhaust is also frequency dependent (low pass filter).

I would estimate a mufflerless stock-NA-ported rotary at 100 dB at WOT, while a ported or turbo rotary (without the turbo) would run about 110 dB at WOT. You will need about 30 dB to get it reasonable, 40 dB to get it to be acceptable and 50 dB to make it quiet.

Bear in mind that the muffler numbers are based on experience at work and the sound estimates are not measured, but guessed based on my experience.

[vex]

Originally Posted by NoDOHC

The attenuation of the sound amplitude occurs naturally in free air.

The sound energy measurement must take place at a specific distance from the source.

A good multi-chambered (perforated pipe-type) muffler is about 30 dB. A high-performance (straight-through) muffler runs between 7 and 15 dB. A straight exhaust is about 5 dB. A presilencer is frequency-dependent attenuation (typically between 5 dB and 20 dB depending on engine speed) they are typically high-pass filters. Actually a straight exhaust is also frequency dependent (low pass filter).

I would estimate a mufflerless stock-NA-ported rotary at 100 dB at WOT, while a ported or turbo rotary (without the turbo) would run about 110 dB at WOT. You will need about 30 dB to get it reasonable, 40 dB to get it to be acceptable and 50 dB to make it quiet.

Bear in mind that the muffler numbers are based on experience at work and the sound estimates are not measured, but guessed based on my experience.

Thanks for the info! However what I was thinking was using electrical theory to do a simple analysis. For instance how does a parallel exhaust setup compare to a series setup? Do using two mufflers on an exhaust system analogous to a parallel electrical circuit?

From my simple research it is not.

I'm still open for suggestions, and barring anything extreme (for instance using acoustic modeling to test for sound in a theoretical system), I may just try to go as large as possible on specific locations.