You can not avoid the attachment. MIME and HTML encoded emails can do what you ask, but each item is an attachment. Also you can not control what we do at the office where we strip email to plain text and drop any suspect attachments. Your email would fail at the offices and here.
But if you have a cooperative email recipient try http://www.htmlgoodies.com/tutors/embed.html and see methods to play it in HTML email.
I want to send an email with audio, not as an attachment. Want the audio to start when email is opened.