Current conventional wisdom regarding rim construction is leaning towards block rims as a preferred method of producing rims. To summarize the conventional wisdom, block rims offer the following advantages:
- Dimensional stability
- The opportunity to use wood speicies that are not easily bent.
- Avoiding the necessity of introducing moisture into lumber that has already been dried.
Obviously the goal in selecting any species of wood or method of construction is to produce a tone appropriate for the type of banjo (old timey, bluegrass, minstrel, etc.) and to fulfill the expectations of the player.
Bluegrass musicians in particular have set notions of how a banjo ought to sound. The banjo greats who emerged after WWII had access to a relatively plentiful supply of prewar banjos that, at the time, were a mere ten or twenty years old. We can assume that not all banjos these early masters played were of the quality as those they finally selected as their primary instruments.
Based on that logic, it is possible to assume that, as in all periods, there were mediocre instruments, poor instruments, and a few excellent instruments produced by Gibson.
All Gibson rims that I know of were steam bent and laminated. Some makers believe that the species of maple near the Gibson factory was particularly suitable, or that over time the metal and wood compressed together to create better response. I return again to the idea that during the year Earl Scruggs' Granada was made, there were three other Granadas that were merely good.
The point I am making here is that what we consider to be the standard (or standards) of perfect tone is, as at all times, partly design and partly a fortunate coming together of materials and workmanship that was not uniform throughout the period or the industry.
By the same logic, rims produced today, all other factors being equal, by the best makers will vary in responsiveness. Furthermore, all other factors are never equal. Every aspect of construction and setup has an impact on tone. Selecting the right bridge is a notable example of how to alter the tone of a banjo dramatically for the least cost and effort.
A maker can tell a lot about rim material simply by flicking a small piece of wood with a fingernail. I call this the "plink" test. Old growth/sunken timber has a noticably bright plink, especially compared to maple cut in modern times. Therefore I do not think that using old growth maple is all hype. Having said that, bluegrass enthusiasts tend to focus narrowly on a single factor -- bridge, tailpiece, rim material, head material -- at the exclusion of other factors. This is not hype per se, but it's easy to get very enthusiastic about a single factor without seeing the whole.
The truth is that most makers don't want to bother tooling up for heavy duty wood bending and gluing. Why should they re invent the wheel when Cooperman and Cox make excellent rim blanks? Block rim construction is popular, so why bother?
The most difficult aspect of making a block rim is getting excellent joints. Let's say a layer of a block rim is set in eight pieces. When cutting angled segments, if your setup is off by a half a degree in angle, by the time you multiply that by the number of joints, you have created a noticable gap somewhere in the rim.
If tight joints are the key, then why wouldn't adding tight splines at each joint be as good accoustically as the best joints in the world? Splines also add to the beaty of block rims by making the joints into decorative elements.
That is my hope in my own block rim construction.