Ajax не принимает ответ на post-запрос

jQuery.post(url,[data],[callback],[dataType]):jqXHR

function myalert(arg1, arg2, arg3)
{
    if (window.XMLHttpRequest)
    {// For IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp=new XMLHttpRequest();
    }
 
    else
    {// For IE6, IE5
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlhttp.onreadystatechange=function()
    {
        if (xmlhttp.readyState==4) // if the data transfer has been completed
        {
            if(xmlhttp.status==200)  // if server response equal "200 OK"
            {
                document.getElementById("resp").innerHTML=xmlhttp.responseText; // recording results in the field
 
            }
 
            else //if server response not equal "200 OK"
            {
                alert('Error while creating connection with server');// error message
            }
        }
 
        else //if the data from the server isn't loaded that
        {
            document.getElementById("resp").innerHTML='Loading...'; // recording notice in the field
        }
    }
    var params="arg1="+arg1+"&arg2="+arg2+"&arg3="+arg3;
    xmlhttp.open("POST","audio_out.php",true); // sending data via POST-method to file output_audio.php
    //Send the proper header information along with the request
    xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xmlhttp.setRequestHeader("Content-length", params.length);
    xmlhttp.setRequestHeader("Connection", "close");
 
    xmlhttp.send(params);
}

console.log(xmlhttp);