Just helping you troubleshoot, but your script dosn't play on my linux box with the latest kernel and alsa. So I'm not sure, but there are 2 possible errors I see.

1. Try this script, it uses play_music instead of play_channel, and puts a loop at the end to keep the script from exiting prematurely.

#!/usr/bin/perl
use strict;
use warnings;
use SDL;
use SDL::Mixer;
use SDL::Music;


my $mixer = SDL::Mixer->new(
    -frequency => MIX_DEFAULT_FREQUENCY, # 22050
    -format    => MIX_DEFAULT_FORMAT,    # AUDIO_S16
    -channels  => MIX_DEFAULT_CHANNELS,  # 8
    -size      => 1024    #higher numbers give sloppy reponse
                          #as buffers continue to empty
);
# provides 8 channels of
# 16 bit audio at 22050 Hz. and a single channel of music.

#background can be mp3,ogg or wav (mp3 needs smpeg libs)
my $mp3  = new SDL::Music('1bb.mp3');

$mixer->music_volume(MIX_MAX_VOLUME); #128

$mixer->play_music( $mp3, 100 ); 

my $done = 0;
while (! $done && ( SDL::GetAudioStatus() 
       == SDL_AUDIO_PLAYING())) {SDL::Delay(1); }
[download]

2. Look for /dev/sequencer in /dev. On my alsa setup there is a link to /dev/sound/sequencer, which is what alsa sets up. Maybe you are missing the link?

See Tk Game Sound demo