Why hollow guitars sound the way they do.
Our fascination with secret chambers is as
old as time. From childhood reading about
the Egyptian pyramids and Batman’s cave to
the modern-day Harry Potter books, something
mysterious and powerful resonates
within us when it comes to hidden rooms. For
centuries, the promise of treasure within has
drawn raiders and archeologists to Giza and
Mesoamerica, seeking knowledge, truth, or
wealth. Wise men knew that anything worth
having was worth preserving in a safe place,
and hidden chambers were intended for that.
In the world of instruments there is treasure as well. For those who eat, sleep, and breathe guitar, the list of likely places to unearth harmonic wealth most certainly includes hollow and semi-hollow instruments. It is no surprise—these chambers echo with the treasured tones of guitar history.
A Solid Perspective
Today, most guitarists forge their vocabulary from solidbody experience and their tone-compass finds “true north” within that limited context. That’s because solid guitars brought costs down for beginners, were “modern” and flashy, and were suited to higher-volume music, especially so in less experienced hands. In the battle of the generations, solid guitars became the weapon of choice for youthful, loud, and aggressive music, but that wasn’t always the case.
Before the era of electric guitars, there were only hollow instruments. These early guitars were engineered to reproduce sound mechanically like all classical instruments. But in an ever-escalating arms race with louder horns and reed instruments, the guitar was out-gunned for the solo spots. In retaliation, guitarists began to experiment with ways to increase volume. At first the fixes were mechanical—birthing the resonator guitars we know today, not to mention some wacky derivations like the 1920s Stroh, which utilized a spun aluminum diaphragm and horn. These instruments were marginally louder, but the tone wasn’t refined enough for most types of music. For a while, it seemed as though the guitar would remain a rhythm instrument within the bigger band context, but soon enough enterprising players were equipping their fat “jazz boxes” with crude electro-mechanical devices coupled to small “amplifiers,” and the game was on.
My introduction to the electric guitar at age 10 was via a big, hollow Gibson with a pair of black-cased P-90s that a camp counselor had brought into the gymnasium for our entertainment. It looked archaic, yet somehow menacing with its array of knobs and lever switch. That promise was delivered when he cranked up a little GA-5 amp, and I heard the Devil’s radio threatening to blow the windows out of the building. I was hooked. Two years after that, I got a solid Fender, but I never forgot the lonesome howl that day in the gym. It’s a tone that I still chase today.
Science Meets Sound
So what makes a hollow guitar tick? In the simplest of terms, it’s the fact that it vibrates more than a solid guitar. But to stop there is an oversimplification. In my years of working alongside aerospace technicians at our skunkworks laboratory (affectionately referred to as “Area 59”), I witnessed endless deflection tests and scans of guitars using a laser vibrometer. This pricey piece of equipment takes a real-time computer “movie” of the minute vibrations of a guitar’s surface, which can be analyzed in order to “see” what you were hearing when a guitar was played.
The relationship between stiffness and frequency response can be mapped out pretty convincingly using this stuff. It reveals to the layperson exactly what good guitar builders have known by the seat of their pants. As the guitar top begins to absorb certain frequencies of vibration from the strings, converting it into movement, the top acts as a kind of filter. The top (and back) are also acting like a microphone diaphragm, picking up the vibrations from the amplifier’s speaker, feeding it back to the strings again. All together, you get a very complex set of reinforcements and cancellations.
Like a natural echo chamber, the size and placement of the instrument’s chamber will determine exactly what result you get. Generally, the larger the chamber, the lower the threshold is for interaction and at a lower frequency. Some builders of semi-hollow electrics harness this by creating several chambers of different sizes to address different frequency ranges. This alters an instrument’s sensitivity. It’s usable sensitivity that I look to create in making a hollow guitar, and that balance takes experience to design and build. That sensitivity can be rewarding to master, but also can be intimidating at first.
In practice, it’s a good idea to first approach a hollow instrument with a clean, low volume setting. This gives the instrument a chance to reveal what it sounds like on its own. As you add volume, you’ll reach a point where your hand technique starts to really trigger the interaction of the amp and the guitar. This is what I call the first sweet spot, and it really rewards the player who knows how to work the strings fearlessly. Then, once you’ve enjoyed that for a while, start cranking it up and hold on. You may not be able to play the way you’re used to, but that’s the whole point. If you weren’t looking for a new ride, you wouldn’t have bought the ticket.
Sometimes, players choose a hollow guitar for the way it looks or the way they think it will make them sound. But the hollow guitar is more than a prop or tool for retro tone. Because of its throaty response and predisposition for singing along with your amplifier, it actually can lead you to play differently. The hollow or semi-hollow guitar’s willingness to partner with you and the amplifier makes it an ideal songwriting collaborator. Once you embrace the places a hollow guitar will take you instead of expecting it to just follow you around to the same old haunts, a whole new world of tonal opportunity awaits. Will you use the knowledge found in the chamber for good or evil? The answer is, of course, howl on.
Noted designer, builder, and player Jol Dantzig founded Hamer Guitars, the first boutique guitar brand, in 1973. Since then, he has worked or recorded with many of the most talented and famous names in music. Today, as the director of Dantzig Guitar Design he continues to help define the art of custom guitar.