Call different file depending on whether checkbox is checked

Javascript newbie here, in need of help and hints. I'm currently calling my audio files this way:

    <div class="playFeatured">
        <audio id="playA" preload='none'>
           <source src='audio/RM-5.1.mp3' type='audio/mpeg' />
           <source src='audio/RM-5.1.ogg' type='audio/ogg' />
        </audio></div>

When the checkbox (#swingBox) is checked, I want to call the audio file from the directory 'audio/swing/*') instead. Here's my current code:

    var swingBox = document.getElementById('swingBox');
    var straightRhythm = $('#playA').find('audio').attr("src");
    $(document).ready(function() {
    if $('#swingBox').prop('checked', true){ 
        $(straightRhythm.slice(0,6) + "swing/" + straight.slice(6););};
    if $('#swingBox').prop('checked', false){
        $(straightRhythm);
    };
    }

Can anyone point me in the right direction? Thanks so much!