Audio 102: Sound Transducers

In a previous blog post, we talked about how sound works, and what sound is. However, in order for us to be able to adjust sound levels, apply effects loops, and amplify the signal we need to be able to convert sound waves into electrical energy. Understanding how this works is not essential to being able to use a sound system effectively, but it provides a helpful context to what we do.

A transducer is an electronic device that does just that; it transduces (converts) energy from one form to another. This term is not specific to sound energy and electrical signals, but that is what we will address here. First we’ll walk through how sound is turned into an electrical signal in a microphone, and secondly we’ll go over how that signal then goes back from being an electrical signal to a sound wave.

A microphone is one type of transducer; it’s job is to take the physical energy of sound waves and transduce or convert it into an electrical signal that can then be amplified. Although there are a number of different types of microphones and each method of transduction is slightly different, there are two major types that we will talk about here. They are dynamic and condenser microphones.

Dynamic microphones are the most common microphones in the church audio world. If you’re not sure what type of microphone your church uses, you likely use a dynamic microphone. Dynamic microphones are relatively simple, durable microphones that don’t require external power to generate an electrical signal.

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Fig. 1: Diagram of a dynamic microphone.*

 

As figure 1 shows, the mechanical energy of a sound wave causes the diaphragm of the microphone to move, which causes the coil to move back and forth around the magnet, which transforms the mechanical energy into electrical energy. The movement of the coil around the magnet causes electrons to move through the wire, which becomes an analogue electrical signal that can be transmitted through wires, sent through processors, and amplified before being sent to speakers.

Dynamic microphones are very similar, except that instead of current being generated by a coil around a magnet, the current is supplied by a power source (such as phantom power or a DC power connection), and the sound waves cause variations in the current, which can then be transmitted, processed, and amplified.

condenser-microphone-1

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Fig. 2: Diagram of a condenser microphone, including detailed diagram of diaphragm and backplate.**

In figure 2, we see a diagram of the diaphragm moving in relationship to pressure fluctuations caused by sound waves. This causes increases and decreases in capacitance and potential, which changes the amount of current that runs through the microphone. These changes are analogous to the changes in current in a dynamic microphone, and can be transmitted, processed, and amplified.

Speakers are another type of transducer. Instead of transducing sound into electrical energy, they take electrical energy and transduce it into sound. When a coil with current running through it is placed near a magnet, the amount of attraction or repulsion between the wire and the magnet depends on the amount of current in the wire and the direction it is travelling. Using these properties, an electrified coil pushes or pulls a cone rapidly to create variations in air pressure, which our ears translate into sound.

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Fig. 3: Cutaway diagram of a loudspeaker; 1 – Magnet; 2 – wire coil; 3 – Suspension; 4 – Diaphragm.

A basic diagram of a speaker would look identical to figure 1, except that instead of sound waves causing an electrical current, the electrical current would cause the diaphragm to create sound. Figure 3 provides a cutaway diagram, which shows how the different parts fit together. The suspension is the part of the speaker (or microphone) which holds the conical diaphragm in place, yet still allows it to vibrate back and forth.

The amount of electrical energy picked up from a microphone is significantly less than is needed to move a speaker. This is why the signal is run through an amplifier before being run to a speaker. Mixer’s and processors are used to affect the signal that goes out to the speaker, and to make sure the volume is correct. For further information on proper mic positioning, mixing, and processing, stay tuned for future blog updates! Also, If you have any questions or if there’s a topic you’d like us to cover that you don’t see here, feel free to contact us using the details at the top of the page!

*Fig. 1 taken from www.pjaviation.co.za/wp-content/uploads/2012/05/image001.gif under GFDL version 1.3.
** Fig. 2 taken from upload.wikimedia.org/wikibooks/en/4/4f/Battery_Powered.jpg and upload.wikimedia.org/wikibooks/en/6/68/Condenser.jpg under GFDL version 1.3.
**Fig. 3 taken from upload.wikimedia.org/wikipedia/commons/7/79/Loudspeaker-bass.png under GFDL version 1.3 and Creative Commons Attribution-Share Alike 3.0 unported license. Image created by Svjo.
Audio 102: Sound Transducers