customized submit varieties – The right way to move the information dynamically to post__in

I’ve under code on my web page

$speakersselected = get_post_meta($post->ID, 'speakersselected', true);
print_r($speakersselected); //getting output (587,585)

        $s_post = array(
          'showposts' => 80, 
          'post_type' => 'speaker',
          'post_status'  => 'publish',
          'post__in'    =>$speakersselected,
           //'post__in'    =>array($speakersselected),
            //'post__in'    => array(587,585),
           );
    
       
     echo"<pre>";
     print_r($s_post);  

Output

if I exploit 'post__in' =>$speakersselected then I get under output

Array
(
    [showposts] => 80
    [post_type] => speaker
    [post_status] => publish
    [post__in] => 587,585
)

if i exploit 'post__in' =>array($speakersselected) then getting under output

Array
(
    [showposts] => 80
    [post_type] => speaker
    [post_status] => publish
    [post__in] => Array
        (
            [0] => 587,585
        )

)

Each the output not working for me

if i add the static information 'post__in' => array(587,585) then it is working for me

Array
(
    [showposts] => 80
    [post_type] => speaker
    [post_status] => publish
    [post__in] => Array
        (
            [0] => 587
            [1] => 585
        )

)

Any thought how one can ship dynamic information in post__in?