Chapter 8. Keeping Things Quiet.|
6705 words. 26 illustrations.
The Problem. Noise and power. EU noise limit. Roadside testing problems.
The Source of Noise. Complex nature of exhaust sound waves. Valve discharge. Noise from a pulsating system. Self-noise induced by joints and edges.
Sound Perceptions. The dB scale. Frequency effects.
Methods of Attenuating Noise. Silencing by the catalyst. Mufflers. The quarter wavelength rule. Frequency and temperature effects. Frequency response. Reflection. Absorption. Helmholtz resonator. Quarter wave resonator. Venturi. Restriction.
Active Silencing. Simple two path switched method. Selectable quiet or sport mode. True active principle. Out of phase sound generated as a counter. More effective at low frequencies.
The Tail Pipe. Slight diffusing action. Velocity effect on sound quality. Location can be important. Sleeving down. Injury potential.
Flow Issues. Pipe entry considerations. Ideal designs.
Practical Silencers. Multiple chambers. Adding interference. Improved designs.
Practical High Performance Systems. An example for a high performance engine with a resonant front section.
Mundane Applications. A typical multi-function production silencer.
Sound Quality. Multi-cylinder sound effects. Results of coupling. A classic switched active system.