J45s changed a lot over the years, from the lightly built live back ones to the more heavily built ones with the massive adjustable ceramic saddles from the mid 50's onward.

To me, the "real" J45 sound is from the lightly built, live back models with a distinctive diagonal dipole mode of vibration that is forced by closely coupled, tapered (not scalloped) lower face braces. It is this diagonal dipole mode which contributes significantly to the "real" J45 sound. If you just want a slope dread, you don't have to bother with any of that, of course. However, the J45 is such an iconic model which ushered in the singer/songwriter era that we investigated it in detail for the book (mobility, modal analysis, modeling etc.) and because it is so interesting we used it to demonstrate X-bracing in the book (plans, building instructions etc.) rather than use the typical Martin dread patterns.

Steve, I have some photos of the bracing somewhere if you would like me to post some.

Steve, it it's not too much trouble, I would like very much to see your photos.

Thanks all for the feedback Gents and the detailed comments Trevor.

My own (modest) research reinforces what I am reading here - which is Gibson changed things up a lot. The photos I see of J-45s with non-scalloped bracing look massively overbraced to me, with a huge bridge plate. I cannot imagine how, with those braces, it would be possible to get a balanced and open sound with good volume.

My own (modest) research reinforces what I am reading here - which is Gibson changed things up a lot. The photos I see of J-45s with non-scalloped bracing look massively overbraced to me, with a huge bridge plate. I cannot imagine how, with those braces, it would be possible to get a balanced and open sound with good volume.

How did they go about making a 'live back' or was that just a result of accident in design? Did they use low wide lower bout back braces?

The photos I see of J-45s with non-scalloped bracing look massively overbraced to me, with a huge bridge plate. I cannot imagine how, with those braces, it would be possible to get a balanced and open sound with good volume.

The live back was likely intentional design (the designers, I think, knew a lot more than they tend to get credited for) but certainly an accident of build. The ones I've worked on were thrown together pretty haphazardly. Remember that the guitar originally sold for $45; very much a budget model. The main reason it had a sunburst was to hide the runout and the general low quality of the top wood. One of the ones our take was modeled on had 1/4" wide top braces with rounded tops, no reinforcement over the X, and I'm pretty sure some of them didn't even have a box joint; just two half braces butted to a continuous one. In the book we do 1/4" gabled braces with tapers. There are 4 back braces. The guitars we liked had all braces 1/4" wide, so no wide/low ones. The backs were quite thin/light mahogany. That the "good" ones ended up with the right T(1,1)2 - T(1,1)3 separation was purely a matter of chance. The thing that matters in replicating a sound is to get the right modes at the right frequencies in a way that can be repeated. So our take is probably structurally unlike any version that Gibson ever produced, but certainly captures the essence of the sound of the ones we like. If you use high quality materials it is very easy to over-build these things, even if you stick with the narrow braces.

The short scale length is certainly a component of the sound, but Gibson used a variety of (short) scale lengths on this model. The fret spacings tended to be fairly random, too, some with a definite hand-cut vibe about them, with odd frets just wrong. We don't advocate that part!

The soft wood bridge plate is a nice touch. I've seen that before in an old 45.
Is it just me or does the neck in the pics look a little suspect? I've never seen a Gibson logo tacked on in that fashion. Plus, a truss rod cover with 3 screw holes is an Asian detail. AFAIK, Gibson has always used truss rod covers with 2 screw holes.