Workshop: Midnight Reso Tinkerings

A couple posts back I showed off my "new" Nat'l Res-O-Tone solid-body reso/electric guitar. I've since given it some real play time both in jamming with the Saturday jam group and also jamming with customers/friends coming into the shop over the weekend. While I liked the tone right off the bat (it was something like the sound of a good 6-string banjo/bright 30s low-end archtop guitar plus more sustain and sweetness) I had the urge to tinker. I especially wanted my low E and A strings to sound more like a traditional resonator guitar: focused, crisp, but rounded/warm.

Being in touch with acoustic design, I know that it's a bit of a fool's errand to expect much bass from a resonator plunked into a solidbody guitar's routed-out cavity. Resos aren't known for extreme warmth, anyhow! That said, my first mod was to drill tiny vent holes all around the edge of the resonator cone itself (above pic). What?! -- you say! -- well, the cone can be replaced, if necessary, but if I cut air-escape holes into the body of the guitar itself I've started devaluing it!

Right off the bat this increased warmth and presence, which I expected, because it makes use of a uke-sized air chamber sitting right under the cone that was shut off before! Using the small drill holes at the end of each reinforcement "spiral" on the cone means that 1) overall there's a negligible change in cone rigidity and 2) the overall area of the holes added is tiny which = good for letting low frequencies escape.

The second thing I started doing was taping off the vent holes in the coverplate. This follows the rule, in general, that a smaller soundhole (or soundhole overall "area") = better bass response while a larger soundhole = better treble response.

I wound up taping off all of them except the two to either side of the pickup. This dramatically changed the sound of the instrument to the point where it now sounds pretty much like a 14-fret reso, though quieter. I'd say on the volume scale we're now talking about the carrying power of a nice flattop.

In yesterday's jam (about 10 strong), Mr. Tom was picking on it for a few songs and while he said he couldn't hear the guitar that well in the driving seat, compadre Forrest and I were wringing our ears a bit. Tom was banging (well, fingerpicking loudly) on the guitar to try to hear himself over the din but he didn't realize that (like most resos) the sound pops right out and forward instead. We could barely hear him sing over it!

At any rate, I made my "permanent" close-off by adding some aluminum foil to the back of the vent holes I wanted covered and then taping them off from behind. I figured this was a classier way to go rather than blue painter's tape stuck to the rear...!

So -- if you have an instrument like this, definitely at least try taping off some of the vent hole clusters to see where your tone goes. I think you'll be very surprised!