THSCC Forums

Hi All,
As some of you know I have been building a game/simulator about fixing cars. Diagnosis is a big part of the game and I want to do a good job representing all of the different types of knock, pinging, rattles, and valve noise. Most of these are fairly straightforward in that they are a directly tied to crank or cam speed. The one thing I am having a hard time figuring out is knock sounds caused by lose external accessories rattling on the engine. Right now my assumption is that the engine has a natural vibration frequency, a rattle caused by a lose component is going to vibrate at that frequency independent of the engine RPM, and that RPM will affect how loud the rattle is depending on how close the RPM is to a 1st, 2nd, 3rd, etc. order harmonic. Is this correct and if so can someone suggest a way to model a curve of RPM vs rattle intensity? I'm thinking about making a cell phone mount for a BP engine and trying to pull accelerometer data out of it.

Interesting! I am not a Mechanical Engineer, so take this with a grain of salt...

My guess is that the fundamental frequency will be of the item that is loose and not the engine. And that if the engine RPM matches one of the 1st, 2nd, etc harmonics you will then get the loose item to experience sympathetic resonance. In short, different things are likely to vibrate at different RPMs on the same engine. Plus you could get noise from loose items via non resonance transfer. Such as bumps in road surface, etc. so... probably harder to model than you think, but given some simple rules, you probably could create something that might sound close enough.

Richard

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.