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Converting sound into electric current - Electronics .. Physics

Electronics

Converting sound into electric current

Electromagnetic waves contribute to the transmission of sound through space, although they are of a different nature from its nature. To achieve this purpose, it is sufficient first to convert the sound into an oscillating electric current inside a microphone inside which there is a thin metal membrane called the drum, which is made in a way that makes it vibrate from the impact of its collision with sound waves and resonate at a frequency equal to their frequency. This membrane is followed by an electromagnet, in whose coil an induced current is generated whose oscillations are identical to the oscillations of the membrane and the sound waves themselves on an equal footing. After that, this current is sent, via electrical wires to the place we want, and then the sound is extracted from it in a process similar to the first but reversed. It is worth noting that the phone is built on this principle, despite the different types of microphones used.

There are limits to using the phone in this way that we cannot cross. Obtaining high sounds requires the use of amplifiers and sound amplifiers. Amplifiers are basically made up of valves and transistors which are the main elements in them. The valve, as its name has changed, allows the current to pass in only one direction, and the simplest type used in the field of amplification is the triode, which consists of a glass tube, evacuated of air, containing three electrical paths: the anode or positive pole, the cathode or negative pole, and between them the control grid through which the electrons pass. The cathode is usually heated by a special heating element separate from the valve. If we connect the positive and negative poles of the battery to the anode and cathode of the valve, we find that the electrons escape from the hot cathode and the anode attracts them, and as a result an electric current is generated in the valve that goes in only one direction. If we reverse this and connect the positive and negative poles of the battery to the cathode and anode of the valve respectively, we find that the current has become zero.

The electrons pass through the control network on their way to the anode. Therefore, any change in the voltage of the latter is sufficient to change the number of electrons flowing inside the valve. The more positive its voltage is relative to the cathode, the greater the electric current flowing. In contrast, the value of the current is reversed the more negative its voltage is than the cathode voltage. If the network is fed with a weak alternating current, we also get an alternating current between the anode and the cathode, but it is much greater than the first current. This is because the power coming out of the anode circuit is not related to the internal power in the network circuit. For this reason, and in order to obtain the greatest possible amplification, when choosing the valve, we must choose the appropriate design for it, and the appropriate polarization of the network in it (i.e. the steady-state voltage in it). Music is nothing but regular sound waves that the microphone, inside the studio, converts into an alternating electric current with the same number of frequencies. The microphone output is then amplified and applied to the recording needle, which is subject to vibration, inside a long, spiral-shaped groove, engraved on a wax cylinder called the master cylinder. This results in a set of protrusions and depressions that are drawn on the walls of the groove and are identical to the sound waves that they left behind. The master cylinder is then electroplated, and images are taken of it that are used to print thousands of copies on plastic cylinders (made of vinyl) called phonographic records. The sound extraction from the cylinder is subject to the same process but in reverse. For this purpose, a studded needle is used that is fixed to a sound pickup and then left to follow the groove engraved on the cylinder. It vibrates as a result of its passage through the channels and depressions in it in the same way as the first one that was used to engrave the groove itself. The pickup then converts the vibrations into alternating electric current. Since a typical lightweight pickup cannot produce more than a hundred milliwatts, an audio frequency amplifier must be used to operate the loudspeaker. The picture shows an amplifier that uses two electronic valves in series and contains two capacitors. Their main function is to facilitate the passage of alternating current and isolate the rest of the amplifier parts from the rest of the direct currents in the rest of the circuit parts. It also contains the anode load resistance through which the current flows. There is also a transformer connecting the device and the loudspeaker. In addition, the drawing shows how a moving coil loudspeaker works: a paper cone is placed in a way that makes it vibrate as a result of the interaction between the permanent magnet field and the phono coil connected to the amplifier output. The larger the cone, the greater the amount of air moving in it and the higher the volume of the audible sound.