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Difficulty: MediumInductors and Transformers

An audio technician is designing a passive crossover network and installs an inductor in series with a low-frequency woofer. Which of the following best explains why the inductor is used in this configuration?

  1. A
    It stores electrical energy in an electrostatic field to boost low-frequency signals.
  2. B
    It converts incoming alternating current audio signals into a steady direct current.
  3. It opposes high-frequency alternating currents while allowing low-frequency signals to pass easily.Answer
  4. D
    It reduces total circuit impedance as signal frequency rises to maximize high-pitch volume.

Answer

The inductor opposes high-frequency alternating currents while allowing low-frequency signals to pass easily.
An inductor generates an opposing electromotive force (back EMF) that increases with the rate of change of current. Because inductive reactance is calculated as XL=2πfLX_L = 2\pi f L, opposition rises with higher signal frequencies. Consequently, placing an inductor in series with a woofer permits low-frequency audio to pass with minimal attenuation while attenuating unwanted high frequencies.

Step-by-Step Solution

1
Identify the relationship between frequency and inductor behavior.
Inductive reactance is defined by the formula XL=2πfLX_L = 2\pi f L, where ff is frequency and LL is inductance.
Understanding how an inductor's opposition changes with frequency determines which signals it blocks or passes.
2
Analyze circuit operation at low versus high audio frequencies.
At low audio frequencies (ff is small), XLX_L is low, presenting almost zero opposition. At high audio frequencies (ff is large), XLX_L is high, presenting strong opposition to current flow.
This behavior creates a low-pass filter when placed in series with a speaker load.
3
Match the electrical characteristics to the speaker application.
The series inductor acts as a low-pass filter (choke), directing bass signals to the woofer while blocking treble frequencies.
Woofers are designed strictly for low-frequency sound reproduction.

Key Concept

Inductive reactance (XL=2πfLX_L = 2\pi f L) increases with frequency, allowing an inductor to block high-frequency AC signals while allowing low-frequency signals to pass.
Estimated Time:1m 0s
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Topics

Inductors and Transformers

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