Great Ukes: Why Did Gibson’s First Banjo Uke Have a Trap Door?


When thinking of high-quality banjo ukuleles, aficionados of this cousin of the regular ukulele often think of the instruments made nearly a century ago by the Gibson Guitar Company. Contemporarily best known for its extensive lines of acoustic and electric guitars, Gibson also produced some really terrific banjo ukes—not too surprising, considering they started manufacturing banjos in 1918. In response to the growing popularity of the ukulele in the 1920s, Gibson introduced its first ukulele banjo, the UB model, sometime around 1925. Commonly known as the Gibson “trap door,” this model’s defining element was its unique two-piece, hinged rear resonator, which was also featured on Gibson’s tenor banjos and banjo mandolins. 

1920s Gibson UB "trapdoor" banjo ukulele

Build-wise, the Gibson UB has a nine-inch-diameter rim (aka shell) made from multiple layers of laminated maple. The rim supports a metal tone ring that secures the uke’s calfskin head. Twenty metal brackets (aka hooks) clamp the tone ring down and provide adjustment for the tension of the head. The UB’s entire pot (the rim, tone ring, etc.), which is larger in diameter than just about any other banjo uke, was directly sourced from the banjo mandolins Gibson made at the time.

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The UB’s neck is solid maple capped with a Brazilian rosewood fingerboard bearing 18 frets and six pearl fret position markers. The instrument shown here has a curvaceous, so-called “python” or “snake” shaped headstock; I’ve also seen examples with headstocks that have straight tapering sides and peak. The tops of both styles of headstock are painted black and have “The Gibson” rendered in silver paint. The UB’s scale length is 14 inches, which is about the same as a concert-sized uke. Back in the 1920s, it was common for all banjo ukuleles to be fitted with steel strings rather than gut strings, as their higher tension gave the instruments more punch and volume.

1920s Gibson advertisement for ukulele banjos

Of course, the Gibson UB’s main feature is its cool “trap door” mechanism, which consists of a flat, two-piece hinged maple resonator trimmed with white ivoroid binding. The larger, moveable portion of the resonator has a small oval soundhole also trimmed in ivoroid. A tiny metal knob just below the soundhole locks the resonator closed. Rotate the knob a half turn and a pair of spring-loaded hinges automatically pops the resonator open. Turning the knob further engages a clip that locks the resonator in the open position. 

So, what does opening or closing the trap door actually do? With the resonator in the open position, the sound of the uke is much louder in the ears of the player. It’s sort of like what the soundports found on the upper bouts of some guitars and regular ukuleles do. But according to the majority of UB uke players—including myself—closing the resonator doesn’t really do much to change either the volume or the tone that’s projected to the audience, which raises the question as to why bother to even have this feature?

gibson headstock for 1920s banjo ukulele

It seems that Gibson came to the same conclusion, as they only made the trap door UB model for about a year before ceasing its production. In its place, Gibson created and produced an entire line of banjo ukes in five models ranging from the affordable, open-backed, six-inch pot UB-1 to the high-end “professional” UB-4 and UB-5 models. These two top-of-the-line models were made of black walnut and featured fingerboards and headstocks with fancy pearl inlays. Both had eight-inch pots with large metal flanges that supported resonators made from highly figured walnut. Metal parts were nickel plated on the UB-4 and gold-plated on the flagship UB-5. All of Gibson’s banjo ukes, including the original trap door UB, are highly sought after and coveted by today’s players and collectors.