$(document).ready(
function() { 
    $("div.switch-image").hover(
        function(){
            $(this).addClass("mouseover");
            var newsrc = $("img.speaker",this).attr("src").replace("_bw","");
            $("img.speaker",this).attr("src",newsrc);
        },
        function(){ 
            $(this).removeClass("mouseover");
            var newsrc = $("img.speaker",this).attr("src").replace(".jpg","_bw.jpg");
            $("img.speaker",this).attr("src",newsrc);
        }
    ); 
}
);