Transmission Loss
Transmission Loss
(OP)
HI
I am designing an exhaust system for a 450cc engine. I have designed the new system out of lightweight materials with a similar internal configuration as the stock item with a range of end cap sizes. I have run the model in Solidworks Flow Simulation to calculate back pressure produced at a certain RPM.
Is there anyway to calculate the approximate dB produced by the exhaust if I know the theoretical pressure and velocity of the gas exiting the silencer??
Thanks for any help in advance
Regards
Graeme
I am designing an exhaust system for a 450cc engine. I have designed the new system out of lightweight materials with a similar internal configuration as the stock item with a range of end cap sizes. I have run the model in Solidworks Flow Simulation to calculate back pressure produced at a certain RPM.
Is there anyway to calculate the approximate dB produced by the exhaust if I know the theoretical pressure and velocity of the gas exiting the silencer??
Thanks for any help in advance
Regards
Graeme





RE: Transmission Loss
P(t)=rho/(4.pi.R).dS(t-R/c)/dt
Where c is the speed of sound in the air between source and receiver, -R/c is the transport delay. Then you just need to analyse the pressure signal at the receiver as you would with measured pressure.
A good book on this is: "Theoretical Acoustics", Philip McCord Morse.
- Steve
RE: Transmission Loss
RE: Transmission Loss
Cheers
Greg Locock
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RE: Transmission Loss
Yes it's a four stroke single cylinder
So if i had a velocity of 150 m/s and a maximum total pressure of 123000 Pa how would I calculate it?
Thankyou for for all the help
Regards
Graeme
RE: Transmission Loss
Pressure variation similar to the red curve in Fig 2 here -
http://www.epi-eng.com/piston_engine_technology/ex...
Or, the sounds heard around 0:40 here but with frequency based or rpm.
http://www.youtube.com/watch?v=_y1Nog5SuM4
I think for the variation in end cap size ( opening diameter(s) or area, or ??) to change the exhaust sound very much it might be a result along the lines of an acoustic "plenum chamber" as shown about 1/3 down the page here -
http://www.mom.gov.sg/Documents/safety-health/fact...
If the end cap succeeds in creating "back pressure" of a few psi in operation the power may be suppressed a bit too.
Some general silencer effects here-
http://www.paraglidingteam.nl/PPGTechnics/sound%20...
RE: Transmission Loss
- Steve