INTRODUCTION

Electro-acoustic is an adjective describing any process involving the transfer of a signal from acoustic to electrical form, or vice versa. Most commonly, transducers such as the microphone or loudspeaker are examples of this process.

In a broad sense, acoustic maybe defined as the generation, transmission and reception of energy in the form of vibrational waves in matter. As the atoms or molecules of a fluid or solid are displaced from their normal configuration an internal elastic restoring force of stiffness arises. Typical examples of such a force include the tensile force produced when a spring is stretched and the increase in pressure produced when a fluid is compressed into a lesser volume.

It is the action of this elastic restoring force, coupled with the inertia of the system, that enables matter to participate in oscillatory vibrations and thereby generate and transmit acoustic waves. The modes of vibration range for the simple sinusoidal vibrations produced in an adjacent air by a mounted tuning fork vibrating at its fundamental frequency, through the complex pattern of vibrations generated by a bowed violin, to the non periodic vibration associated with a noise or an explosion.

Fundamental Concepts of Acoustics

The studyof acoustics revolves around the generation, propagation and reception ofmechanical waves and vibrations.

made to the quantity under evaluation and the reference level. It is also instructive to note that the decibel level is primarily determined by the magnitude of the absolute value of the power level. That is, if the magnitude of two different power levels differ by a factor of 100 then the decibel levels differ by 20 dB.

Decibel addition. In many cases cumulative effects of multiple acoustical sources have to be evaluated. In this case the individual sound levels should be summed.