The speed of sound depends on the elastic and inertial properties of the particular medium.
Gases
In air, the speed of sound depends on the temperature of the air, at 20°C the speed of sound is 343ms-1.
In a perfect gas the equation is:
where
- γ = ratio of specific heats
- P0 = pressure [Pa]
- ρ0 = density [kgm-3]
- T = temperature [K]
- r = specific gas constant [JK-1kg-1]
The speed of sound is proportional to the square root of the absolute temperature.
where
- T0 = 273K
- c0 = 331ms-1
- T = gas temperature [K]
- tc = gas temperature [°C]
Liquids
For liquids, the speed of sound is much higher than it is for gases because the density increase for a given pressure increase is much smaller in liquids than in gases. For a pure substance near its critical temperature and pressure, however, the sound speeds of the vapour and liquid phases are not very different.
Solids
the speed of transverse waves depends on the shear modulus and the density of the medium. Longitudinal waves in solids depend on the these two factors with the addition of a dependence on compressibility.
Exhaust System Design
Exhaust system design is primarily about managing the gases ejected from an engine. These waste products are transported away from the engine using an exhaust system. The main features that must be considered are: Acoustic design – Acoustic Ducts, Acoustic Filter Elements (eg Silencer), Flow Noise, Shell radiated noise Construction and manufacturing process.
In all of the acoustic calculations inside the exhaust you need to take into account the temperature of the gas on the speed of sound.
Noise & Vibration
Noise – any unwanted disturbance, such as undesirable sound waves in a car passenger cabin. The word “noise” is derived from the same Latin root as the word “nausea”.
Vibration – An oscillation about an equilibrium position or shape.