CAT Technical Skills 3 — Questions and Answers
Question 1: What is the purpose of a delay line in a distributed audio system with multiple speaker zones?
- Increase amplifier headroom
- Synchronize audio with distant speakers to avoid echo (Correct answer)
- Reduce DC offset
- Boost bass frequencies
Correct answer: Synchronize audio with distant speakers to avoid echo
Delay lines time-align audio signals so that sound from distant speakers arrives at listeners simultaneously with nearby speakers, preventing echo or comb filtering.
Question 2: In a 70V distributed speaker system, what is the advantage of using a step-down transformer at each speaker?
- It amplifies the signal
- It allows multiple speakers to be wired in parallel without impedance issues (Correct answer)
- It converts the signal from analog to digital
- It filters out low frequencies
Correct answer: It allows multiple speakers to be wired in parallel without impedance issues
70V transformers allow many speakers to be wired in parallel on a single amplifier output while maintaining a manageable load impedance.
Question 3: What is 'feedback' in an audio system and what is its primary cause?
- Hum caused by a ground loop
- A howling sound caused by a microphone picking up its own amplified output (Correct answer)
- Clipping distortion from overdriving an amplifier
- Low-frequency rumble from mechanical vibration
Correct answer: A howling sound caused by a microphone picking up its own amplified output
Acoustic feedback occurs when a microphone picks up sound from a speaker and re-amplifies it in a continuous loop, creating a howl or squeal.
Question 4: What does 'THD' measure in an audio amplifier?
- Total High-frequency Delay
- Total Harmonic Distortion (Correct answer)
- Thermal Heat Dissipation
- Transient High-amplitude Detection
Correct answer: Total Harmonic Distortion
Total Harmonic Distortion (THD) measures the ratio of harmonic overtones added by the amplifier to the original signal, expressed as a percentage.
Question 5: A commercial audio technician is troubleshooting a 60 Hz hum in a system. What is the most likely cause?
- Incorrect EQ settings
- Ground loop between two pieces of equipment (Correct answer)
- Defective compression driver
- Insufficient amplifier gain
Correct answer: Ground loop between two pieces of equipment
A 60 Hz hum (matching AC power frequency in the US) is a classic symptom of a ground loop caused by multiple ground paths between equipment.
Question 6: What is the recommended dB level for nominal line-level signals in professional (+4 dBu) audio equipment?
- -10 dBV
- +4 dBu (Correct answer)
- +20 dBu
- 0 dBFS
Correct answer: +4 dBu
+4 dBu (approximately 1.23V RMS) is the standard nominal operating level for professional balanced audio equipment.
Question 7: Which amplifier class is most commonly used in high-efficiency commercial audio amplifiers due to its ability to switch between output states?
- Class A
- Class B
- Class AB
- Class D (Correct answer)
Correct answer: Class D
Class D amplifiers use pulse-width modulation switching to achieve efficiencies above 90%, making them ideal for commercial installs where heat and power consumption matter.
CAT Technical Skills 3
What is the purpose of a delay line in a distributed audio system with multiple speaker zones?