Limiting download speeds with PHP

I have this code here, however i want to limit the speed the user can download at, how would i implement this into this code;

header("Content-type: application/force-download");

    header("Content-Transfer-Encoding: Binary");

    header("Content-length: ".filesize("uploads/$filename"));

    header("Content-disposition: attachment; filename=\"$origname");

    readfile("uploads/$filename");

Thanks!

This is what i tried;

$download_rate = 100;

$origname = get_file_name($file[0]);

header("Content-type: application/force-download");

    header("Content-Transfer-Encoding: Binary");

    header("Content-length: ".filesize("uploads/$filename"));

    header("Content-disposition: attachment; filename=\'$origname'");



    $local_file = "uploads/$origname";

// flush content flush();

// open file stream

$file = fopen($local_file, "r");



while (!feof($file)) {



    // send the current file part to the browser

    print fread($file, round($download_rate * 1024));



    // flush the content to the browser

    flush();



    // sleep one second

    sleep(1);

}



// close file stream

fclose($file);

Why doesn't this work?