News:

"The phone is a remarkably complex, simple device,
and very rarely ever needs repairs, once you fix them." - Dan/Panther

Main Menu

How does a "sound powered" phone work?

Started by Greg G., January 08, 2011, 06:13:08 AM

Previous topic - Next topic

rdelius

Sound powered telephones would not have carbon transmitters. Carbon transmitters need a source of direct current to modulate to produce a varying current. Sound powered sets use a diaphragm coupled to a coil surrounded by a strong magnetic field to produce a similar but weaker current.the receiver uses the current flowing through the coil and a strong magnit for bias to move a diaphragm to produce sound waves. I have connected sound powered handsets between a radio studio and the transmitter building and was surprised how loud they were (only a couple of miles though).You can take 2 telephone rec capsules and connect them together to act as a sound powered intercom. They are low impedance so they will not work as well as the higher impedance sound powered capsules
Robby

AMCer

#16
Resurrecting this old thread because I can answer the big question: How does it work (which wasn't answered in the thread).

Sound powered phones are just that, phones that use the microphone to generate the power needed to drive the receivers.  They do not use power (do NOT connect a battery to them as suggested in one post).  You just hook them together and they work. You would think that one little microphone wouldn't have enough power to drive multiple receivers or go very far but, they do.  You can connect many of them on one circuit (just parallel them) and the damned things still work.

Some watch stations (officer watches) do have them connected into an amplified multi-line intercom box (so the officer doesn't have to pick up and hold a phone) but, it's sometimes hard to understand it so the station will also have a non-powered handset that the officer can use. The handset is also used if power to the intercom is lost.

They are still the main communication system on Navy ships because 1) they work really well even in noisy environments  ...and...   2) They require no power and are resilient to damage.

One funny thing about them, when you first start using them, you can't understand a word being said but, after you get used to them, it becomes second nature and you understand everything with no problems.

unbeldi

Quote from: AMCer on October 20, 2016, 11:54:06 PM
Resurrecting this old thread because I can answer the big question: How does it work (which wasn't answered in the thread).

Sound powered phones are just that, phones that use the microphone to generate the power needed to drive the receivers.  They do not use power (do NOT connect a battery to them as suggested in one post).  You just hook them together and they work. You would think that one little microphone wouldn't have enough power to drive multiple receivers or go very far but, they do.  You can connect many of them on one circuit (just parallel them) and the damned things still work.

Some watch stations (officer watches) do have them connected into an amplified multi-line intercom box (so the officer doesn't have to pick up and hold a phone) but, it's sometimes hard to understand it so the station will also have a non-powered handset that the officer can use. The handset is also used if power to the intercom is lost.

They are still the main communication system on Navy ships because 1) they work really well even in noisy environments  ...and...   2) They require no power and are resilient to damage.

One funny thing about them, when you first start using them, you can't understand a word being said but, after you get used to them, it becomes second nature and you understand everything with no problems.

Well, to be fair to all before you, you did not actually answer the question either.
To say, just plug them together and they work, or they do not use power, is not an explanation.  The statement that the microphone generates power gets a little closer to the truth, but is misleading and does not really help to understand it either, as "power" is usually interpreted not in the physical sense of being energy converted or work performed per per unit time, but as having some source of constant electrical energy pool to operate a circuit.

A sound powered telephone system uses dynamic microphones, which work on the principle of an electric dynamo. Either a coil of wires is moved within a magnetic field or a magnetic field is varied around a fixed coil, by the mechanical pressure of sound against a transducer, a type of diaphragm. This induces a varying electric potential across the wire (coil) and an electric current flows in the rhythm of the sound imposed onto the microphone membrane if the circuit is closed via an amplifier or simply with a receiver element at the other end of the intercom line.  The dynamic microphone operates in reverse manner of a typical loudspeaker, in which the varying electric audio signal causes the membrane to move from electromechanical action.

andy1702

I just got 3 souind powered telephones as part of a job lot. It's prompted me to do a bit of research about them and apparently sound powered telephones are still a legal requirement to be fitted to US registered shipping to this very day. The authorities won't accept any electric or battery system in case the power source becomes disconnected in an emergency.

Every US Navy ship still has to be fitted with these phones.

The clever part is the signal is normally transmitted as AC because low voltage AC travels a lot better over a distance than DC does. I've seen references to 30 miles between handsets being possible!
Call me on C*net 0246 81 290 from the UK
or (+44) 246 81 290 from the rest of the world.

For telephone videos search Andys Shed on Youtube.

HowardPgh

In most any telephone circuit, the transmitted sound is alternating current.  I the sound power system the microphone generates the alternating current and directly transmits it through through the wire to the receiver.  In a local battery system,
the carbon granules are compressed by the sound vibrating the diaphragm. This compression causes their resistance to vary with the sound. Since the carbon granules are in series with a battery and the primary of an induction coil (or transformer), the varying current of this circuit causes the electric field of the primary coil to vary with the sound. This induces an alternating current in the secondary coil which is transmitted through the wire to the receiver. In a local battery system there is no DC on the lines between the telephones.  In common battery this AC is superimposed on the DC in the line (wires) that is used to power the transmitter. Since DC is fatal to receivers a capacitor (condenser) is placed in series with receiver to block the Direct current and only allow alternating current to reach it. So simple, even I could explain the theory of telephony. :D
Howard

countryman

Weren't dynamic transmitter elements also used in some of the early telephone patents?
The breaktrough of telephony came with carbon microphones, which allowed a significant amplification of the signal.
I have a pair of sound powered phones that originate from a local coal mine. Actually, the manufacturer still makes them. They are required by code for certain safety applications and cost a horrible amount of money when new and certified.
I never tried or photographed mine, still on the "to do list" ;-)
They use identical dynamic elements for transmit and receive and also as a "ringer". Each phone has a magneto with a frequency of (estimated) 400Hz depending on the speed, making a howling sound in both elements.
https://www.fhf.de/index.php?pid=27630&lid=4

rdelius

Bell's  wooden receivers doubled as transmitters before the carbon transmitter ( Blake) was developed.This was a sound powered system. The carbon microphone along with a battery and induction coil allowed longer transmission distances