[BigV]

Originally Posted by BigV

Isn't growler the name for the communication device onboard a submarine or other naval vessel? (not looking it up, that is).

It's *also* a "Sound-powered telephone", aka, "growler".

The microphone transducer converts sound pressure from a user's voice into a minute electrical current, which is then converted back to sound by a transducer at the other end. The most significant distinction between ordinary telephones and sound-powered telephones is in the operation of the microphone. Since the microphones used in most telephones are designed to modulate a supplied electrical current they cannot be used in sound-powered transducers. Rather, most sound-powered telephones use a dynamic microphone. A common approach to transducer design is the balanced armature design because of its efficiency. The number of simultaneous listeners is limited because there is no amplification of the signal.

A sound-powered telephone circuit can be as simple as two handsets connected together with a pair of wires, which is defined as the "talk" portion of the circuit. Talk circuits can be realized over a pair of wires that are 50 km (30 miles) long. More complex circuits include magnetos, selector switches and bells to allow one user to select and call another, which is defined as the "calling" portion of the circuit. The voice communication ("talk") circuit is completely separate from the "call" circuit, allowing communication to take place without external power.

Sound-powered telephones are widely used on naval vessels. A typical example on a U.S. Navy ship is the "JL" circuit which is used by the lookouts to report visual contacts to the pilot house and the Combat Information Center (CIC). In this case there would be five stations on the circuit (stern lookout, port lookout, starboard lookout, pilot house and CIC).

Now *that's* a big boat.