By connecting a microphone to the amplifier, you can reproduce the speaker's voice at an increased volume. At the same time, you can speak in front of the microphone quietly, without straining, and all visitors to the hall where the speakers are installed will hear your speech.
Instructions
Step 1
Remember that amplification of speech with a microphone, amplifier and speakers is considered to be reproduction only from a physical point of view, and not from a legal point of view. According to the last of these criteria, it is more suitable for the definition of public performance - and then only if the entrance to the hall is free, or there is a significant number of people who do not belong to the usual family circle.
Step 2
The way the microphone is connected to the amplifier depends on the physical principle of the first one. If the microphone is dynamic, when speaking into it, it itself generates an alternating voltage, the amplitude and shape of which depend on the volume and nature of the sounds spoken. But the voltage generated by such a microphone is negligible. If the amplifier is not sensitive enough, place a preamplifier in front of its input. And if the frequency response of the input stage of the amplifier is designed for a different type of microphone, equip this preamplifier with correction circuits to avoid bubbling.
Step 3
The carbon microphone requires an external power source and takes on some of the work to pre-amplify the signal. Connect it in series with the primary winding of the matching transformer and apply the voltage specified in the microphone specifications to this circuit. Connect the secondary winding of the transformer to the input of the amplifier, which, due to the significant amplitude of the signal, in some cases can only consist of an output stage (this solution is found in some old megaphones).
Step 4
The electret microphone contains a small MOSFET preamplifier in the housing. When connected, it requires polarity: the terminal connected to the case is negative. Connect it to a power source (voltage of 1, 5 or 3 V, depending on the type) through a resistor of several kilo-ohms, and remove the signal through a non-polar capacitor with a capacity of several tenths of a microfarad. The sound card already has everything necessary for the operation of an electret microphone: a voltage source, a resistor, and a capacitor. Outside, to the red jack, you only need to connect the microphone itself, designed for 1.5 V.
Step 5
If the microphone is located near the speakers, acoustic feedback is possible, which manifests itself in the form of a hum of changing pitch, drowning out the voice. It can be eliminated by moving the microphone away from the speakers, lowering the volume, using complex sound processing devices or special computer programs. But a differential dynamic microphone will give much better results. Its membrane communicates with the surrounding space from both sides. If the speakers are far away, the sound affects the membrane also from two sides with opposite signs, and it does not vibrate. When speaking in front of the microphone, the sound affects the membrane only from one side, and the microphone perceives it in the same way as a normal dynamic one.
