CEA Speaker Systems & Amplification 2 — Questions and Answers
Question 1: A speaker has a sensitivity of 100 dB SPL (1W/1m). What SPL is produced at 1 meter when driven with 100 watts?
- 110 dB
- 120 dB (Correct answer)
- 130 dB
- 140 dB
Correct answer: 120 dB
SPL = sensitivity + 10×log10(power): 10×log10(100) = 20 dB, so 100 + 20 = 120 dB SPL.
Question 2: What is the primary sonic advantage of bi-amping a two-way speaker system?
- It eliminates the need for any crossover network
- Each amplifier handles only its frequency band, reducing intermodulation distortion (Correct answer)
- It doubles the speaker cabinet's maximum SPL output
- It allows two mismatched speaker brands to work together
Correct answer: Each amplifier handles only its frequency band, reducing intermodulation distortion
With bi-amping, separate amplifiers handle high and low frequencies independently, so intermodulation between bass and treble signals is eliminated and each amp operates with greater headroom.
Question 3: Reversing the polarity of one speaker in a stereo pair most noticeably causes:
- Increased high-frequency brightness
- Bass cancellation and a diffuse, unfocused stereo image (Correct answer)
- Higher overall SPL output
- Increased distortion at high playback levels
Correct answer: Bass cancellation and a diffuse, unfocused stereo image
Out-of-phase speakers cause their long-wavelength bass frequencies to cancel, and the stereo image spreads unnaturally rather than focusing in the center.
Question 4: How does a ported (bass reflex) cabinet differ from a sealed cabinet in terms of low-frequency behavior?
- It uses a passive radiator instead of a woofer cone
- Its tuned port extends low-frequency output below the driver's natural resonance (Correct answer)
- It requires less amplifier power for the same midrange SPL
- It eliminates the need for a low-frequency crossover
Correct answer: Its tuned port extends low-frequency output below the driver's natural resonance
The tuned port acts as a Helmholtz resonator, reinforcing bass output at and below the driver's resonant frequency and extending usable low-frequency response.
Question 5: What does the horizontal dispersion specification of a loudspeaker describe?
- The angular range over which the speaker maintains consistent frequency response in the horizontal plane (Correct answer)
- The number of discrete audio channels the speaker can reproduce
- The distance at which SPL drops 6 dB below the on-axis measurement
- The maximum horizontal tilt angle before acoustic feedback occurs
Correct answer: The angular range over which the speaker maintains consistent frequency response in the horizontal plane
Horizontal dispersion is the angular coverage (e.g., ±60°) within which frequency response remains relatively flat, which is critical for determining audience coverage in live sound.
Question 6: Amplifier headroom is best defined as:
- The physical rack space above the amplifier in a touring case
- The margin in dB between the normal operating level and the onset of clipping (Correct answer)
- The frequency range above 10 kHz that the amplifier reproduces cleanly
- The minimum speaker impedance the amplifier can safely drive
Correct answer: The margin in dB between the normal operating level and the onset of clipping
Headroom is the dB gap between the typical program level and the amplifier's clip point, providing a safety margin that allows transient peaks to pass without distortion.
Question 7: When integrating a subwoofer with full-range speakers, the crossover point is most commonly set in which frequency range?
- 20–40 Hz
- 60–120 Hz (Correct answer)
- 200–400 Hz
- 800 Hz–1 kHz
Correct answer: 60–120 Hz
A 60–120 Hz crossover smoothly hands off bass to the subwoofer while the full-range speakers handle midrange and above, providing flat overall response without a gap or overlap.
CEA Speaker Systems & Amplification 2
A speaker has a sensitivity of 100 dB SPL (1W/1m).
What SPL is produced at 1 meter when driven with 100 watts?