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Difficulty: MediumCapacitors

An audio technician connects a capacitor in series with a high-frequency speaker (tweeter) inside a multi-speaker enclosure. What is the primary electrical reason for using a capacitor in this configuration?

  1. A
    It stores energy in a magnetic field to boost low-frequency bass signals delivered to the speaker.
  2. It easily passes high-frequency signals due to lower capacitive reactance while blocking low frequencies.Answer
  3. C
    It blocks high-frequency signals and allows direct current and low audio frequencies to pass freely.
  4. D
    It acts as a permanent insulator that converts excess electrical voltage into heat at all audio frequencies.

Answer

The capacitor is used because it easily passes high-frequency signals due to lower capacitive reactance while blocking low frequencies.
Capacitive reactance (XC=12πfCX_C = \frac{1}{2\pi f C}) is inversely proportional to the frequency of the electrical signal. For high-frequency signals directed to a tweeter, the capacitor offers very low opposition (low reactance), allowing the high-frequency audio to pass smoothly. At low frequencies or DC, the reactance becomes extremely high, blocking low-frequency bass currents that could overheat or damage the delicate tweeter voice coil.

Step-by-Step Solution

1
Analyze the relationship between frequency and capacitive reactance (XCX_C).
Capacitive reactance is inversely proportional to frequency, governed by the formula XC=12πfCX_C = \frac{1}{2\pi f C}.
Understanding how reactance changes with frequency is essential for determining how AC audio signals behave across the component.
2
Determine the effect on high versus low audio frequencies.
At high frequencies (treble), XCX_C is very low, presenting minimal opposition to current; at low frequencies (bass) and DC (f=0f = 0), XCX_C becomes extremely large, effectively blocking the signal.
Tweeters are designed to handle only high-frequency signals, so placing a capacitor in series forms a high-pass filter that protects the tweeter from damaging low frequencies.

Key Concept

Capacitors exhibit capacitive reactance inversely proportional to frequency, acting as high-pass filters in series audio crossover circuits.
Estimated Time:1m 0s
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Capacitors

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