1920s The Ernst Double-Backed Mandolin

Back in the teens and '20s, volume was king. Why else would anyone play tenor banjo? Oops! Juuuuust kidding...

Hugo Ernst, a maker out of New Jersey, patented  a "double-backed" design to help increase volume for fretted instruments. This mandolin's "top layer" is build as-normal, but the "actual back" is suspended about 1/2" above the "physical back" of the instrument. That creates a second sound chamber under the "regular" chamber and the secondary little soundhole on the upper bout is where that lower chamber is ported.

I think the most important thing here is that this "second back" isolates the "normal back" from your belly and thus the player isn't dampening the instrument with their body. That does give this instrument a pure, loud, clean voice -- similar to how using a "Tone Guard" cage helps keep a Gibson-style instrument sounding its best. Whether you care about that maybe-extra-5% overall, though, is another thing entirely!

This one was just in for a customer's light setup work -- compensation added to the bridge and setup -- and I was glad to have it in the shop as I've wanted to hear another one of these. I played one a long time ago but it was nice to freshen-up the memory.