Complete information on Public Address System (PAS)

Public Address System is now an important part of our daily life. The system is used to produce the recorded sound and the reinforce or increase the sound for announcement purposes.

Though one can say that system is easy and simple but there may be many problems in successful reproduction or reinforcement of the sound. Some of them may be listed as follows:

The place where the PA system is to be installed, decides upon the many factors in designing the system. The number of speakers and microphones and their proper installation points depend very much upon the location.

There will be a completely different design of a PA system in a theatre than on a football ground or in a hospital or at a railway station or a place of work ship every building has its own acoustic problem, sometimes simple, more often difficult.

The area of coverage height of the roof, reflective surfaces are of major importance, and the nature of the function. The main things which are responsible for such variations are the need and quality of the sound tolerance to external pick up by the microphones etc.

The P.A. system should be so designed that the sound of the person of the instrument is faithfully reproduced out. The quality or pitch of the sound should be as uniform as possible in the desired coverage area.

Acoustic feedback is the greatest enemy of all acoustic engineers, the more so as its fundamental for which there is not cure-only careful compromise. The acoustic feedback is the feedback of sound from the speaker to the microphone.

Such feedback is more serious when the area is confined one. The effect of such feedback is the hawl back. The feedback problem becomes more severe when the gain of the system is high. Thus it limits the gain of the system.

It is possible to reduce this effect by using highly directional microphones and by the utmost care in the choice and positioning of the loudspeakers in relation to the microphone.

Another cause of the feedback may be due to the use of microphones having an unequal response, i.e. a peak output of same point in the audio range. This may mean that the gain over the whole of the audio range suffers. A considerable energy loss is resulted due to this.

The feedback eliminated by the microphone is very small hence, are tear chances of interference produced by the induced currents from the other equipments. This is why a shielded cable adequately earthed at one central point should be used. The microphone wiring should be away from the loudspeaker lines.

The output of microphone depends upon the distance from the speaker. It varies according to the inverse of the square of this distance. The voltage developed by microphone at a distance 60 cm. will be one-quarter of the voltage developed at a distance 30 cm.

When a microphone is mounted on a rostrum or in a pulpit in any fixed position it should be placed so as to allow the close approach. It should be arranged so that the speaker’s face is not covered in any way.

The loudspeakers should be able to handle both low and high frequency extermit.es of the audio range. The type of loudspeakers available although varying in size and power handling capacity can be classified as follows:

(a) Cabinet type with conventional cone.

(b) Horn type having inherently high efficiency.

(c) Column type employing a number of cone type units arranged one above the other and the whole having directional characteristics and concentrating the

When no current flows through the coil, a constant magnetic field exists at the attracted diaphragm plate is stationary. However as shown an alternate current flows through the coil the magnetic field will become strong or we, depending on the direction of current. The diaphragm is even attracted to a great or lesser extent by the magnetic poles is thus caused to vibrate.