No sound in Mathematica 8 under Ubuntu 11.04

[hameerabbasi]

Hello,

Mathematica 8, under Ubuntu 11.04, gives no sound. I get the following messages when playing any sound:

Java::excptn: A Java exception occurred: javax.sound.midi.MidiUnavailableException
    at javax.sound.midi.MidiSystem.getDefaultDeviceWrapper(MidiSystem.java:1078)
    at javax.sound.midi.MidiSystem.getReceiver(MidiSystem.java:240)
    at javax.sound.midi.MidiSystem.getSequencer(MidiSystem.java:442)
    at javax.sound.midi.MidiSystem.getSequencer(MidiSystem.java:348)
Caused by: java.lang.IllegalArgumentException: Requested device not installed
    at javax.sound.midi.MidiSystem.getDefaultDevice(MidiSystem.java:1130)
    at javax.sound.midi.MidiSystem.getDefaultDeviceWrapper(MidiSystem.java:1076)
    ... 13 more.

Java::excptn: A Java exception occurred: javax.sound.midi.MidiUnavailableException
    at javax.sound.midi.MidiSystem.getDefaultDeviceWrapper(MidiSystem.java:1078)
    at javax.sound.midi.MidiSystem.getSynthesizer(MidiSystem.java:307)
Caused by: java.lang.IllegalArgumentException: Requested device not installed
    at javax.sound.midi.MidiSystem.getDefaultDevice(MidiSystem.java:1130)
    at javax.sound.midi.MidiSystem.getDefaultDeviceWrapper(MidiSystem.java:1076)
    ... 11 more.

I have tried everything here, here and here. I get the following output in init.m modifications (as I prefer to change $SoundDisplayFunction directly, even if I use Unprotect[]):

Set::wrsym: Symbol $SoundDisplayFunction is Protected.

After that, the same thing if I play any sound. Any idea to get sound fully functional?