The History Of Sound Holes
April 1, 2022
Hello Everyone - Happy Friday!
People ask me all the time about sound holes. There's a long history of sound holes in stringed instruments - from the earliest gourd/gut instruments, to Stradivarius's violins, to your favorite Folkcraft Instruments dulcimers.
Sound holes serve two purposes: 1) they add a nice decorative touch to an instrument, and 2) they allow the top of the instrument to move freely. Number two is very, very important. Let's talk about how a dulcimer makes sound that we can hear, and then come back to sound holes.
When you pluck/pick/strum a string, it starts oscillating. This speed of oscillation (speed of oscillation determines the note you hear!) is dependent on a couple of important factors - the VSL (Vibrating String Length), and the string's mass/tension. Let's take a dulcimer fretboard and put some strings on it. When you strum the strings, you won't hear much. The strings do not make enough sound for most of us to hear. So we need something to amplify the string's vibration, and make it into something for humans to enjoy.
So let's add a body to our fretboard and strings. Now the energy from your pick is transferred to the top of an instrument. This instrument is typically something hollow, that is relatively light, and relatively stiff. When we strum the strings, the energy from your pick starts the strings to oscillating. Some of that energy goes through the bridge, through the fretboard, and into the top of your dulcimer. This process gets the top (aka soundboard, now you know why!) to start oscillating up and down, in time with the side-by-side motion of your strings.
As the top goes up and down, pressure waves in the air above your top are created. The pressure waves go out in all directions, and reach your ears moments later. Your eardrums (along with a few other anatomical bits connected to your eardrums) convert the pressure waves into electricity, which your brain interprets as sound.
There are a lot of complicating factors in this whole process - the strings and top are kind of obvious, but the sides and back of an instrument start vibrating, too. And then your legs act as dampers, stopping the vibration. (A Galax performance back helps with this issue!) What woods do you use for your instrument? Something really light, and really resonant, might be perfect for maximum volume. But have a tone quality you don't like. The mass of the instrument affects how well it vibrates, so this affects the volume of your dulcimer, too.
It's complicated. The variables are all over the place, so we're always experimenting, and always referring back to our experience building instruments when we make recommendations.
But back to sound holes!
As the top moves up and down, it creates pressure waves outside the dulcimer, which we end up hearing as sound. But how about inside your dulcimer? Same thing, except that you probably can't hear it. But we run into a problem - these pressure waves inside the instrument make it hard for the top to "move". Imagine stuffing a snare drum full of fiberglass insulation. The drum head won't move well, and it won't sound good. Same thing for your dulcimer top - reduced oscillation (from confined pressure waves) hurts the tone.
So...
We put sound holes into the top (or back or sides) of every dulcimer. This allows the air to move in and move out, and keeps the top free to oscillate, and make the pressure waves we want for our ears to hear. The sound doesn't actually come out of the sound holes - it comes off of the top of your instrument. (99 percent, anyway - there ARE pressure waves inside that our brain will also interpret as sound.)
Sound holes are decorative, and allow the top to vibrate freely. Their shape has a miniscule effect on the sound of your instrument - by far the most important factor is the combined size of the sound holes. Too big, and the dulcimer sounds bad, and too small, the sound gets muffled.
Now you know the whole story. Thanks for reading!