[alsa-devel] Speaker burnout

[Eliot Blennerhassett]

On 31/03/15 23:43, David Henningsson wrote:
> 
> 
> On 2015-03-31 12:06, Nikita N. wrote:
>>> If you have any concrete examples (alsa-info please!) of speakers that
>>> can be burned out, and you know a maximum speaker volume where this
>> As we said, that is not our bug, we are not audio experts, nor any of us
>> is interested in audio matters.
> 
> Here's my suggestion how to move forward on this:
> 
>  1) Gather consensus that limit the maximum volume on internal speakers
> is the right way forward. Takashi, Clemens, anyone against that strategy?

I'm not sure about this (though in the end it doesn't affect me).  Just
running some experiments on my laptop. (HDA intel PCH sound)

Playing some ordinary music, the level from the internal speakers is
comfortable when master and PCM gains are set to maximum.

At this setting, enabling the internal mic feedthrough with mic boost
set to maximum,  feedback happens when mic playback gain is at -6dB
(max=+12dB).
The signal when recorded is 1325Hz rail to rail square wave.

My point is that in this case for normal usage the maximum output is
fine, I'd even say it is required.  So limiting output would not be a
good idea.
Also when using the mic for speech capture (with headphones for output),
a gain greater than the 'feedback inducing' one is likely to be useful.

So it is (only?) the pathological case of feeding mic direct to speakers
that is problematic.

Given that we can't fix the hardware or wacky user behaviour,
My suggestion would be to either limit, or hide completely the various
"Mic Playback" controls that enable direct feed from input to output.
What is the use case for this anyway? - karaoke?

Given that this goes against the "expose everything in the hardware",
maybe have a module option that can unhide these controls if anybody
actually wants to use them.
--
Eliot