How to Make a 1-Watt Audio Amplifier

from Hacking Electronics illustrated Diy Guide For Makers & Hobbyists - PDF DOWNLOAD

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224 Hacking Electronics

Another figure that is normally stated with the speaker is the power. This specifies how hard the loudspeaker can be driven before the coil will get too hot and burn out. For a small loudspeaker such as one you might put in a small radio receiver, values of 250 mW and up are not untypical. As you progress toward the kind of speakers you would use with a hi-fi set, you will see figures in the tens of watts, or even hundreds of watts.

It is very hard to build speakers that can cover the whole range of audio frequencies, which is generally standardized as 20 Hz up to 20 kHz. So you will often find hi-fi speakers that group a number of speakers into a single box. This might be a “woofer” (for low frequencies) and a “tweeter” (for high frequencies). Because woofers cannot keep up with the high frequencies, a module called a “crossover network” is used to separate the low and high frequencies and drive the two types of speakers separately. Sometimes this is taken a step further and three drive units are used: one for bass, one for mid-range tones, and a tweeter for high frequencies.

The human ear can pick out the direction of a high-frequency sound very easily. If you hear a bird tweeting in a tree, you will probably be able to look straight at it without having to think about where it is. The same is not true of low frequencies. For this reason, surround-sound systems often have a single lowfrequency “woofer” and a number of other speakers that handle midrange and higher frequencies. This makes life easier, because bass speakers have to be much larger than higher-frequency units in order to push large amounts of air about relatively slowly to produce bass sounds.