Table 7-1.--Shipboard Announcing Systems

Table 7-1.--Shipboard Announcing Systems--Continued

Importance

Readiness Class

System

Circuit

Aircraft Maintenance and

51MC

handling control

Unassigned

52MC

Ship Administrative

53MC

Repair officer's control

54MC

55MC

Sonar Service

Unassigned

56MC

57MC

Unassigned

Hanger Deck Damage Control

58MC

SAMID Alert

59MC

* - Central amplifier systems.

Each installed announcing system aboard ship is

Magnetic Microphone

assigned an IC circuit designation in the MC series.

Table 7-1 lists the systems and their circuit designations

The magnetic, or moving-armature, microphone

and the importance and readiness classification for each

(fig. 7-1) consists of a permanent magnet and a coil of

circuit. These systems, however, are not all installed in

wire, inside of which is a small armature. Sound waves

any one ship.

impinging on the diaphragm cause the diaphragm to

In this chapter, we will discuss some of the more

vibrate. This vibration is transmitted through the drive

common systems that are installed on board ship today

rod to the armature, which vibrates in a magnetic field,

and the announcing equipment used with the systems.

thus changing the magnetic flux through the armature.

When the armature is in its normal position, midway

ANNOUNCING EQUIPMENT

between the two poles, the magnetic flux is established

All amplified voice systems consist basically of an

across the air gap with no resultant flux in the armature.

amplifier, a microphone, and a loudspeaker. The

microphone converts the sound energy into electrical

When a compression wave strikes the diaphragm,

energy having the same waveform as the sound energy.

the armature is deflected to the right. The flux path is

The output from the microphone is applied as a signal

directed from the north pole of the magnet across the

voltage to the amplifier. The output power from the

reduced gap at the upper right, down through the

amplifier has the same waveform as the sound energy

armature, and round to the south pole of the magnet.

that is applied to the microphone. The loudspeaker

reconverts the electrical energy from the amplifier into

sound energy at a higher volume level than the original

sound. In shipboard installations, many loudspeakers

are operated from the same amplifier. Each loudspeaker

produces sound having the same waveform as the

original sound applied to the microphone.

MICROPHONES

A microphone is a device that converts sound

energy into electrical energy. All types of microphones

have a metal diaphragm that responds to the vibrations

of the sound waves, and some means of changing this

mechanical vibration into corresponding electrical

signals. The most widely used microphones are the (1)

Figure 7-1.--Magnetic micropbone.

magnetic, (2) dynamic, (3) crystal, and (4) carbon types.

7-3