How A Speaker Works 101

How a speaker works 101

    One of the many questions asked in a world full of music is how does a speaker make the sound that it does with simple electronic pulses? First we must skip through a few steps such as the source (CD player, Ipod, etc) which sends out a signal to a preamplifier/processor which sends a boosted signal to the amplifier.

    Once the speaker receives the signal from the amplifier it must first go through some type of a filter/crossover. A crossover is the brains of the operation when it comes to a speaker and affects your sound more than you know. The crossover will generally be passive; however, active crossovers are becoming more common. We will be focusing on the passive crossover for this article.

    In order to understand what a speaker does we must first understand the basics of a crossover. The main parts of a crossover are inductors, resistors and capacitors and these parts ultimately define your final impedance by how much they impede the flow of current, regardless of the frequency.

    The resistor functions as it is called, it resists the flow of current regardless of the frequency, does not change the phase or any aspects of the signal. Their most basic form is to consume the incoming power and turn it into heat. In an ideal world of speakers you would not have to use a resistor.

    The capacitor impedes the flow of current, but it is not independent to a frequency. The impedance of a capacitor is inversely related to frequency. Example, when the frequency of a signal is doubled the capacitor will impede the current by half as it did at a lower frequency. On the flip side, if you half the frequency received by the capacitor it will double its impedance to the signal.

    Examples to how it is used: A single capacitor in a series position, tied to a resistor would be a high pass filter (it lets the high frequencies pass through). There comes a point that a frequency will be so low that it allows nothing through. On the opposite fence, an inductor (not mentioned yet) tied to a resistor would be a low pass filter.

    The inductor/choke/coil is kind of the opposite of a capacitor. While the inductor is similar to a capacitor in that it changes impedance with the frequency it receives is the opposite. The impedance will actually increase as the frequency increases.

    All these pieces eventually form a puzzle called a crossover; unfortunately a whole other article (many articles) can be written on crossovers. The crossovers main function though is to take the incoming signal, divide the frequencies and send them to the drivers that can reproduce that signal.

            Examples:             
            High Frequency: Super Tweeters, Tweeters
            Mid Frequency: Midrange, Midbass/Woofer
            Low Frequency: Woofer, Subwoofer
    
    Once the signal has processed through the crossover the technology is similar across all the aforementioned drivers. Speaker drivers are composed of many parts, but the essential parts that make it tick are composed of an electromagnet, a permanent magnet and a voice coil.

    When the drivers receive a signal, it is charging the electromagnet/voice coil. The voice coil is large hollow cylinder made up of a magnetic metal like iron which is then wrapped around several times with wire. When electrical current is ran though the wire it forms a field around the coil, in response magnetizing the metal within the coil. The voice coil is mounted in the center of a larger (permanent) magnet, as the polarity of the voice coil changes the permanent magnet opposes the charge of the voice coil which is what causes the coil to move forward or backwards. 

    We can now think of these electrical signals as sound waves, faster positive/negative movements result in higher frequency sounds where as slower electrical signal result in lower frequency sounds. 
 
    The voice is attached to a diaphragm of some type. The cone/diaphragm is anchored to the basket/mounting surface with a surround which helps keep the motion of the diaphragm/cone controlled. Since woofers/midrange drivers have larger movement their voice coil will be attached to a spider which helps reinforce what the surround is doing in controlling the diaphragm.

    So in conclusion, the amplifier sends out a series of positive and negative signals, the crossover takes these signals and divides them up to the right driver for the job. Once the drivers have received the signal, magnets are engaged to move a diaphragm which vibrates the air in front of it translating into sound you can hear with your ears.       

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