CAT Problem Solving and Troubleshooting 3 — Questions and Answers
Question 1: A passive loudspeaker measures 0 ohms across its terminals with an ohmmeter. This indicates:
- The driver is operating normally
- A shorted voice coil or wiring (Correct answer)
- An open crossover inductor
- Correct impedance for an 8-ohm speaker
Correct answer: A shorted voice coil or wiring
Zero ohms on a speaker terminal reading indicates a short circuit, most commonly a shorted voice coil or wiring fault.
Question 2: You plug a ¼-inch TRS balanced output into an unbalanced ¼-inch TS input and notice increased noise. The most appropriate fix is:
- Use a TRS-to-XLR adapter
- Use a direct box or balanced-to-unbalanced interface (Correct answer)
- Increase the output gain to overcome the noise
- Replace the cable with a longer one
Correct answer: Use a direct box or balanced-to-unbalanced interface
A direct box or impedance-matching interface properly converts the balanced signal to unbalanced while rejecting common-mode noise.
Question 3: During sound check, the subwoofers produce output but the tops do not. Both are connected to a stereo amplifier. What should you verify first?
- The amplifier's channel bridging switch or mode setting (Correct answer)
- The DSP high-pass filter cutoff
- The console fader levels
- The AC voltage at the rack
Correct answer: The amplifier's channel bridging switch or mode setting
A bridging or mono-sum switch on the amplifier can disable one channel's independent output, routing all power to the sub connected to it.
Question 4: A wireless microphone receiver shows full RF signal strength but the audio output is silent. The most likely cause is:
- Transmitter squelch set too high
- Incorrect audio output level on the receiver
- Mismatched RF frequency between transmitter and receiver (Correct answer)
- Low battery in the receiver
Correct answer: Mismatched RF frequency between transmitter and receiver
If RF is strong but audio is absent, the transmitter and receiver are likely tuned to different frequencies or channels.
Question 5: An in-ear monitor system produces a high-pitched whine only when the beltpack is within 3 feet of the transmitter antenna. This is caused by:
- RF overload or desensitization at the beltpack receiver (Correct answer)
- Insufficient battery power in the transmitter
- Incorrect EQ preset on the IEM system
- Open circuit in the earphone cable
Correct answer: RF overload or desensitization at the beltpack receiver
Proximity-induced whine in IEM systems is typically RF overload (desense) caused by the beltpack receiver being too close to the transmitter's radiated field.
Question 6: After connecting a new digital snake, you notice a consistent 20ms of latency added to the signal path. What is the most likely explanation?
- Incorrect clock source causing sample-rate conversion
- The snake's internal A/D and D/A conversion processing time (Correct answer)
- A ground loop in the analog returns
- An incorrect EQ curve in the DSP
Correct answer: The snake's internal A/D and D/A conversion processing time
Digital stage boxes introduce a fixed, predictable latency due to the analog-to-digital and digital-to-analog conversion processes and internal buffering.
Question 7: A line array cluster produces comb filtering artifacts in the coverage zone. The first corrective action should be:
- Replace the high-frequency drivers
- Verify cabinet splay angles and inter-element delay alignment (Correct answer)
- Increase the subwoofer level
- Switch from stereo to mono
Correct answer: Verify cabinet splay angles and inter-element delay alignment
Comb filtering in arrays is caused by improper splay angles or time misalignment between adjacent cabinets, which creates destructive interference.
CAT Problem Solving and Troubleshooting 3
A passive loudspeaker measures 0 ohms across its terminals with an ohmmeter.
This indicates: