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684 ⏐⏐⏐ SERIES AND PARALLEL ac CIRCUITS<br />

but at least you should now be able to converse with some intelligence<br />

about the system.<br />

Speaker Systems<br />

The best reproduction of sound is obtained using a different speaker for<br />

the low-, mid-, and high-frequency regions. Although the typical audio<br />

range for the human ear is from about 100 Hz to 20 kHz, speakers are<br />

available from 20 Hz to 40 kHz. For the low-frequency range usually<br />

extending from about 20 Hz to 300 Hz, a speaker referred to as a<br />

woofer is used. Of the three speakers, it is normally the largest. The<br />

mid-range speaker is typically smaller in size and covers the range from<br />

about 100 Hz to 5 kHz. The tweeter, as it is normally called, is usually<br />

the smallest of the three speakers and typically covers the range from<br />

about 2 kHz to 25 kHz. There is an overlap of frequencies to ensure that<br />

frequencies aren’t lost in those regions where the response of one drops<br />

off and the other takes over. A great deal more about the range of each<br />

speaker and their dB response (a term you may have heard when discussing<br />

speaker response) will be covered in detail in Chapter 23.<br />

One popular method for hooking up the three speakers is the crossover<br />

configuration of Fig. 15.104. Note that it is nothing more than a<br />

parallel network with a speaker in each branch and full applied voltage<br />

across each branch. The added elements (inductors and capacitors)<br />

were carefully chosen to set the range of response for each speaker.<br />

Note that each speaker is labeled with an impedance level and associated<br />

frequency. This type of information is typical when purchasing a<br />

quality speaker. It immediately identifies the type of speaker and reveals<br />

at which frequency it will have its maximum response. A detailed<br />

analysis of the same network will be included in Section 23.15. For<br />

now, however, it should prove interesting to determine the total impedance<br />

of each branch at specific frequencies to see if indeed the response<br />

of one will far outweigh the response of the other two. Since an amplifier<br />

with an output impedance of 8 � is to be employed, maximum<br />

+<br />

V i<br />

–<br />

Cmid = 47 �F<br />

Llow = 3.3 mH<br />

8 �<br />

Woofer<br />

Lmid = 270 �H<br />

8 �<br />

Midrange<br />

Chigh = 3.9 �F<br />

8 �<br />

Tweeter<br />

FIG. 15.104<br />

Crossover speaker system.<br />

a c

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