220-1101 Mobile Devices Practice Question
A user reports that their smartphone emits no sound from the bottom speaker (used for speakerphone and media playback). The earpiece works during phone calls, and audio through wired headphones is normal. The volume is turned up and the phone is not in silent mode. The technician has verified that the software audio settings are correct. Which of the following components is MOST likely faulty?
⚠ Common exam trap
CompTIA often tests the misconception that a single audio codec failure would cause all audio to fail, but in reality, the codec has multiple independent output channels, and a fault in the bottom speaker's dedicated amplifier or transducer is the most likely cause when only that speaker is silent.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Bottom speaker
The bottom speaker is the dedicated transducer for speakerphone and media playback audio. Since the earpiece (top speaker) and wired headphone output both work correctly, the audio codec and signal path are intact up to the bottom speaker's amplifier or voice coil. A failure of the bottom speaker itself—such as an open voice coil, torn diaphragm, or corroded contacts—would selectively silence only that output while leaving all other audio paths functional.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Bottom speaker
Why this is correct
The bottom speaker is a dedicated physical transducer used exclusively for speakerphone, media playback, ringer, and alarm sounds. Its failure—due to an open voice coil, torn diaphragm, or blocked/grille debris—would completely silence those outputs while leaving the earpiece and headphone/Bluetooth paths functional, because those utilize separate speaker drivers and independent wiring traces. The symptom of one specific output being dead while others work clearly isolates the fault to the bottom speaker itself.
- ✗
Audio codec chip
Why it's wrong here
The audio codec chip (which integrates the DAC and amplifier drivers) receives all digital audio and distributes analog signals to every audio output: earpiece, headphones, and bottom speaker. If this chip were faulty, the failure would manifest as loss of audio from all outputs simultaneously, not just one transducer. Since the user still hears sound through the earpiece and headphones, the codec is demonstrably processing and delivering analog audio correctly, ruling it out as the cause of the bottom speaker silence.
- ✗
Battery
Why it's wrong here
The battery provides main DC power to the entire phone, including both the audio codec and all speakers; a failing battery generally causes system-wide symptoms such as random shutdowns, sudden power loss, or inability to boot. It would not selectively disable one audio output while leaving other transducers powered and operational—the phone remains energized and other audio paths produce sound. Thus, battery degradation cannot account for an isolated bottom-speaker failure, because electrical power is still reaching the rest of the audio subsystem.
- ✗
Proximity sensor
Why it's wrong here
The proximity sensor is an IR-based detector that disables the touchscreen when the phone is pressed to the ear during a call, preventing accidental taps; it has no connection to audio routing, amplification, or speaker activation. Speakerphone mode is toggled by the call app or user, not by the proximity sensor, so a failed proximity sensor would only cause screen behavior issues, not a silent bottom speaker. Its function is entirely outside the audio output chain, making it a red herring for this symptom.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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