<ul class="event-list">
<?php
    $speaker_posts = new WP_Query( array( 'post_type' => 'speakers'));
    if ( $speaker_posts->have_posts() ) :
        while ( $speaker_posts->have_posts() ) : $speaker_posts->the_post(); ?>

<?php

  $img_url = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'headshot' );

?>

<li class="module">
<a class='iframe' href="<?php the_permalink(); ?>">
   <div class="portrait">

    <div class="portrait headshot" title="<?php the_title_attribute(); ?>">
        <?php echo the_post_thumbnail('medium'); ?></div>
</div>

    <div class="inline-content">

        <div id="custom-bg" style="background-image: url('<?php echo $image[0]; ?>')"></div>
             <div class="title"><?php the_title_attribute(); ?></div>
             <p class="smalljobtitle"><?php the_field('job_title'); ?></p>
    </div>
</a>

</li>
    <?php endwhile; ?>
<?php endif; ?>
</ul>