Why is voice chat not working on my server

Why doesn’t voice chat work on my server?

here is my server.cfg



//Basic settings
net_maxfilesize 64
sv_minrate 20000
sv_maxrate 0
sv_minupdaterate 13
sv_maxupdaterate 66
fps_max 500
cl_cmdrate 101
cl_updaterate 101
rate 15000
sv_maxcmdrate 30
sv_mincmdrate 13

//download stuff
//sv_loadingurl "localhost/DAXfloodModLoad.php"
//sv_downloadurl "localhost/garrysmod"
sv_loadingurl "camdax.dyndns-free.com/DAXfloodModLoad.php"
//sv_downloadurl "http://camdax.dyndns-free.com/garrysmod"
sv_allowdownload 1
sv_allowupload 1

// voice communication
sv_voiceenable 1
sv_alltalk 1


[editline]5th January 2013[/editline]

I had to set sv_alltalk to 3. it works now