This is an excellent overview of harp therapy (opens in new window): http://www.harptherapyjournal.com/what-is-harp-therapy.html

Know also that other instruments can be used in this work, most notably the guitar, dulcimer, keyboard, kalimba, flute, voice and other instruments that are not too loud for a healthcare setting. For more information, visit the Harp for Healing/Certified Clinical Musician site.