Thank you very much for the response. ^_^
In the process of getting the terminal output that you requested (see below), I may have stumbled onto the source of the problem:
In brief, I almost exclusively use a set of wireless headphones when expecting to listen to something on the computer in question (when in Ubuntu, at least), but have the volume of the "Built-in Audio Analog Stereo" (so-named under "Output device" on my taskbar) device--which corresponds to my laptop speakers--muted. The audio-level for the headphones seems to be separate, and this hasn't caused problems before that I recall.
I forget quite how it happened, but I presumably had my laptop speakers unmuted when I ran the command that you gave to me, and the sound played through them! It looks as though the game is insisting on using the laptop speakers, even when they're muted and the headphones are connected.
Running the game with the headphones on and the laptop speakers muted results in no sound; if I then raise the volume of the laptop speakers, the sound seems to play through them--and not through the headphones.
One way or another, here is the requested terminal output:
[I] Startup:173 Starting Arx Libertatis 1.1.2
[I] Application:227 Using config file "/home/ian/.config/arx/cfg.ini"
[I] SDLWindow:71 Using SDL 1.2.15
[I] OpenGLRenderer:123 Using OpenGL 3.0 Mesa 9.2.1
[I] OpenGLRenderer:126 ├─ Vendor: X.Org
[I] OpenGLRenderer:129 └─ Device: Gallium 0.4 on AMD RV635
[I] ArxGame:561 Changed window size to 1024x746
[I] SDLInputBackend:237 Using SDL input
AL lib: LoadConfigFromFile: found new block 'reverb'
AL lib: LoadConfigFromFile: found new block 'alsa'
AL lib: LoadConfigFromFile: found new block 'oss'
AL lib: LoadConfigFromFile: found new block 'solaris'
AL lib: LoadConfigFromFile: found new block 'mmdevapi'
AL lib: LoadConfigFromFile: found new block 'dsound'
AL lib: LoadConfigFromFile: found new block 'winmm'
AL lib: LoadConfigFromFile: found new block 'port'
AL lib: LoadConfigFromFile: found new block 'pulse'
AL lib: LoadConfigFromFile: found new block 'wave'
AL lib: GetConfigValue: Key general:hrtf_tables not found
AL lib: GetConfigValue: Key general:rt-prio not found
AL lib: GetConfigValue: Key general:resampler not found
AL lib: GetConfigValue: Key general:trap-alc-error not found
AL lib: GetConfigValue: Key general:trap-al-error not found
AL lib: GetConfigValue: Key reverb:boost not found
AL lib: GetConfigValue: Key reverb:emulate-eax not found
AL lib: GetConfigValue: Key general:drivers not found
AL lib: GetConfigValue: Key pulse:spawn-server not found
AL lib: alc_initconfig: Initialized backend "pulse"
AL lib: alc_initconfig: Added "pulse" for playback
AL lib: alc_initconfig: Added "pulse" for capture
AL lib: GetConfigValue: Key general:excludefx not found
AL lib: GetConfigValue: Key general:default-reverb not found
AL lib: GetConfigValue: Key general:channels not found
AL lib: GetConfigValue: Key general:sample-type not found
AL lib: GetConfigValue: Key general:format not found
AL lib: GetConfigValue: Key general:frequency not found
AL lib: GetConfigValue: Key general:periods not found
AL lib: GetConfigValue: Key general:period_size not found
AL lib: GetConfigValue: Key general:sources not found
AL lib: GetConfigValue: Key general:slots not found
AL lib: GetConfigValue: Key general:sends not found
AL lib: GetConfigValue: Key general:cf_level not found
AL lib: alcOpenDevice: Created device 0x20f70f0, "Built-in Audio Analog Stereo"
AL lib: UpdateDeviceParams: Format pre-setup: Stereo, Float, 44100hz, 1024 update size x4
AL lib: stream_buffer_attr_callback: minreq=8192, tlength=24576, prebuf=0
AL lib: UpdateDeviceParams: Format post-setup: Stereo, Float, 44100hz, 1024 update size x4
AL lib: GetConfigValue: Key general:layout_stereo not found
AL lib: GetConfigValue: Key general:layout not found
AL lib: GetConfigValue: Key general:hrtf not found
AL lib: UpdateDeviceParams: HRTF disabled
AL lib: UpdateDeviceParams: BS2B disabled
AL lib: UpdateDeviceParams: Stereo duplication disabled
AL lib: alcCreateContext: Created context 0x20d6da0
[I] OpenALBackend:133 Using OpenAL Soft 1.1 ALSOFT 1.14 without EFX
[I] OpenALBackend:137 └─ Vendor: OpenAL Community
[I] PakReader:546 Loaded PAK "/home/ian/.local/share/arx/data.pak"
[I] PakReader:546 Loaded PAK "/home/ian/.local/share/arx/loc.pak"
[I] PakReader:546 Loaded PAK "/home/ian/.local/share/arx/data2.pak"
[I] PakReader:546 Loaded PAK "/home/ian/.local/share/arx/sfx.pak"
[I] PakReader:546 Loaded PAK "/home/ian/.local/share/arx/speech.pak"
[I] PakReader:610 Added dir "/home/ian/.local/share/arx/graph"
[I] PakReader:610 Added dir "/home/ian/.local/share/arx/misc"
[I] SaveGame:70 Using save game dir "/home/ian/.local/share/arx/save"
[I] SaveGame:178 └─ "New" 2014-10-29 0:57:52
[I] Localisation:124 Using language from config file: english
[I] ScriptEvent:538 Scripting system initialized with 176 commands and 186 suppressions
[I] FontCache:57 Using FreeType 2.4.12
[I] Text:396 Loaded font "misc/arx.ttf" with sizes 62, 34, 21, 43, 22, 22, 22
[I] Core:550 Launching splash screens.
[I] Core:696 Initialized Arx Fatalis (full game)
AL lib: FreeContext: 0x20d6da0
AL lib: FreeDevice: 0x20f70f0
[I] Core:3627 Clean shutdown