Noise suppression Introduction

Noise suppression

Introduction 
Engine noise 
Methods of suppressing noise
Construction and materials 

INTRODUCTION
1. Airport regulations and aircraft noise certification requirements, all of which govern the maximum  noise level aircraft are permitted to produce, have made jet engine noise suppression one of the most important fields of research.

Fig. 19-1 Comparative noise levels of various engine types.

2. The unit that is commonly used to express noise annoyance is the Effective Perceived Noise deciBel (EPNdB). It takes into account the pitch as well as the sound pressure (deciBel) and makes allowance for the duration of an aircraft flyover. Fig. 19-1 compares the noise levels of various jet engine types.
3. Airframe self-generated noise is a factor in an aircraft's overall noise signature, but the principal noise source is the engine.

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