Anyone who has played an autoharp, mountain dulcimer, or other stringed instrument that is is is held by a strap or placed on the lap has experienced the pleasant vibrations coming from the instrument’s back. “I can feel it sing against my chest”, is a compliment often payed to a well designed autoharp. The experience can be like hugging a purring kitty. The entire instrument vibrates and the back has a big effect on volume and tone.
Sometimes it is a problem when you take your purring kitty to a jam or performance that is dominated by a bunch of slobbery, barking dogs. Your quiet instrument cannot be heard and playing harder removes much of the control and subtlety that you’ve practiced so much to achieve.
A lot of volume and tone is lost when contact with the lap or torso absorbs the backs vibrations. Guitars, mandolins, and (especially) fiddles can be held in such a way as to leave much of the back free but with autoharps and mountain dulcimers, the player actually presses the the instrument against the body.
A second back, fastened to the instrument with a small gap between, can make a noticeable improvement in volume and tone. Many mountain dulcimers feature double backs in their original construction. Some are merely placed on a temporary arrangement sometimes called a “possom board”. The double back allows the instrument to vibrate freely without the dampening effect.
I have fashioned a very basic double back resonator for an autoharp that I’m building. It’s inexpensive and can be easily removed for bare back riding. I cut it to shape with my bandsaw from a 12″ x 24″ x 3/16″ x 5 ply birch “hobby panel” that I purchased from Menard’s. After sanding and sealing it with shellac, I sprayed it with three coats of lacquer.
I had already fastened four rubber bumpers to the back of the autoharp so I removed them to locate the 5/32″ screw holes on the resonator. The bumpers were reinstalled, this time on the outside of the new resonator and into the existing holes. To create a space between the autoharp’s back I used felt piano punchings as spacers but washers or small wooden blocks would work equally.
The new resonator adds only 3/8″ to the height of the body so the autoharp will still fit in its case. This autoharp has exposed and finished ply sides so the hobby ply matches nicely. The panel could be easily stained to match almost any instrument’s appointments.