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My laptop has built-in front left, front right, rear left, rear right

and

...

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subwoofer and something is strange. When I set channel output to 5.1 or 4.1 and external speakers are disconnected, then front left and front right work as expected but

built-in

...

subwoofer is heard only if I test rear left channel (wrong channel

mapping?)

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/sound/pc

...

i/hda/hda_codec.c?id=cd4035e814b04c009ece9939396d06370c53ed44

Seem only two pairs of stereo speakers and internal subwoofer at left channel before this patch

ALSA: hda - Enable surround speakers (when line out is also present)

On my laptop case "Virtual SurroundSound" is written . When I test front

left

and rear left, I hear distinct sound, so it would mean it's from two

different

sources of sound.

The driver use more than two channels only after David 's patch

But all internal speakers of the notebook are at front of the user, The 3D sound effect is quite different from your external 5.1 speakers

Do you mean your 5930g need champ {FL FR RL RR LFE }?

This can be easily implemented by using "swap center/lfe" switch for those codec support R/L swap

http://git.alsa-project.org/?p=alsa-lib.git;a=blob_plain;f=test/chmap.c;hb=H...

http://git.alsa-project.org/?p=alsa-lib.git;a=tree;f=src/conf/pcm;hb=HEAD

If codec does not support R/L swap, your 4.1 swap chmap need 5.0 routing

Do you expect pulseaudio show 4.1 swap(5.0) profile for internal speakers and 4.1 and 5.1 profiles for external speakers ?