CEA Speaker Systems & Amplification 1 — Questions and Answers
Question 1: What distinguishes a Class D amplifier from Class A or Class AB designs?
- It operates at lower voltage to reduce heat
- It uses pulse-width modulation to switch output transistors rapidly (Correct answer)
- It has no negative feedback loop
- It is designed exclusively for subwoofer frequencies
Correct answer: It uses pulse-width modulation to switch output transistors rapidly
Class D amplifiers use pulse-width modulation (PWM) to rapidly switch output transistors between fully on and fully off states, achieving very high efficiency compared to linear amplifier classes.
Question 2: Two 8-ohm speakers are wired in parallel. What is the combined impedance presented to the amplifier?
- 16 ohms
- 8 ohms
- 4 ohms (Correct answer)
- 2 ohms
Correct answer: 4 ohms
Two equal impedances in parallel result in half the impedance of a single unit: 8 ÷ 2 = 4 ohms.
Question 3: Speaker sensitivity is standardized as the SPL measured at what reference distance and input power?
- 1 meter with 1 watt (Correct answer)
- 1 foot with 1 milliwatt
- 3 meters with 10 watts
- 1 meter with 2 watts
Correct answer: 1 meter with 1 watt
Speaker sensitivity is defined as the dB SPL measured at 1 meter with 1 watt (or 2.83 V RMS into 8 ohms) of pink noise input.
Question 4: What is the primary function of a passive crossover network inside a speaker cabinet?
- To boost bass frequencies for added punch
- To route specific frequency ranges to the appropriate drivers (Correct answer)
- To match the speaker's impedance to the amplifier output impedance
- To protect the amplifier from back-EMF generated by the woofer
Correct answer: To route specific frequency ranges to the appropriate drivers
A passive crossover divides the audio spectrum so each driver—woofer, midrange, tweeter—receives only the frequency band it can reproduce efficiently.
Question 5: How does a speaker's RMS power rating differ from its peak power rating?
- RMS is the instantaneous maximum; peak is the long-term average
- RMS reflects continuous power handling; peak is the short-term transient maximum (Correct answer)
- RMS measures voltage capacity; peak measures current capacity
- They are equivalent values expressed in different measurement domains
Correct answer: RMS reflects continuous power handling; peak is the short-term transient maximum
RMS (continuous) power is what the speaker can handle indefinitely without damage, while peak power is the brief transient capacity, typically 2–4× the RMS value.
Question 6: Damping factor in a power amplifier is defined as the ratio of:
- Load impedance to amplifier output impedance (Correct answer)
- Amplifier output impedance to load impedance
- Input voltage to output voltage
- Maximum power to rated power
Correct answer: Load impedance to amplifier output impedance
Damping factor = speaker (load) impedance ÷ amplifier output impedance; a higher value means the amplifier more effectively controls the speaker cone's back-EMF motion.
Question 7: Which amplifier class is most widely used in professional audio systems because it balances low distortion with reasonable efficiency?
- Class A
- Class B
- Class AB (Correct answer)
- Class C
Correct answer: Class AB
Class AB amplifiers bias both output transistors slightly on, eliminating crossover distortion while achieving far better efficiency than pure Class A, making them the professional audio standard.
CEA Speaker Systems & Amplification 1
What distinguishes a Class D amplifier from Class A or Class AB designs?