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One of the most important audio components for the faithful reproduction of sounds is the speaker. The speaker is a device by which to convert electric signals into sound waves. In this and subsequent issues, we will explain the role of the speaker in faithful sound reproduction. |
| Role of the Speaker As shown in the figure below, signals to be transmitted are amplified with an amplifier. The amplified electric signals are fed to the speaker: the paper cone of the speaker moves back and forth in response to the electric signals, causing air to vibrate, and the vibration of air is transmitted to the listener as sound waves. |
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| How does the Speaker Produce Sounds? Speakers can be classified into four types, according to the mechanism by which electric signals are converted into sound waves: the permanent magnet type, capacitive type, electro-magnetic type and piezoelectric type. We will explain the working principle of the speaker, taking, as an example, a permanent magnet type speaker (the so-called cone-shaped dynamic speaker) which is often installed in a car. If electric current flows through the voice coil from behind towards you, the cone paper is driven upwards, as indicated by the Flemingﾕs left hand rule. On the contrary, if electric current flows in the opposite direction, the cone paper is driven downward. A repetition of these tiny movements makes sounds. |
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| Representative Speaker Units to be Installed in a Car The speaker converts electric signals into the back-and-forth movement of the paper cone using the voice coil. If the speaker did not have the paper cone, it could not put air into vibration, and thus could not produce sounds. Thus, the paper cone is an important element of the speaker, and its quality and shape greatly affect the quality of reproduced sounds. To design a speaker unit to be installed in a car, utmost care should be taken to select the optimal material for the cone paper, because the car interior is often exposed to high temperature and moisture. ●Cone-shaped speaker The vibrating plate is often called a "cone," because it is shaped like a cone. Usually, the vibrating plate (paper cone) is supported at two points. It is supported by the frame at its base edges and by the voice coil and damper at its apex. Cone configurations In reality, the cone may take various configurations. We will introduce several representative cone configurations. |
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| ●Dome-shaped speaker The dome-shaped speaker, like the cone-shaped speaker, directly puts air into vibration through a vibrating plate (diaphragm), thereby emitting sounds in the air. However, in contrast with the cone-shaped speaker, the vibrating plate of the dome-shaped speaker takes a convex semicircular shape like a dome, has a voice coil connected at its periphery, and is supported at its edges. ※The dome-shaped speaker is often used for reproduction of high frequency sounds (tweeter), and thus the movements it is subject to are smaller in amplitude than those observed in a speaker for low-frequency signals. Therefore, its edges serve as a damper as well as a support. |
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| ●Horn-shaped speaker In contrast with the cone- and dome-shaped speakers, which emit sound waves directly into the air, this speaker guides sound waves generated at the vibrating plate (diaphragm) through a horn to emit them into the air, thereby facilitating the matching of the sound waves with air. The speakers we have introduced above are generally used in cars. Among them, the cone-shaped speaker is most widely used, and is easily incorporated into a full-range unit, or as a woofer, or as a squawker into a two-way or three-way unit. The cone-shaped speaker is suitable for a unit with high output, or for reproduction of low frequencies or heavy sounds; the dome-shaped speaker is best for high frequencies, and the conical horn speaker works well for intermediate and high frequencies. |
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In the next issue, we will explain the performance of the speaker. | |||
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