Let’s digress for a moment and speak in gross generalizations about concepts of piano tone.
I have come to the conclusion, specifically reinforced by Udo Steingraeber, that there are fundamentally 2 approaches to piano tone; high rim tension and low rim tension. (don’t bust my chops on theoretical details, remember this is gross generalization).
Low rim tension is characterized, IN MY OPINION, by Bosendorfer, Förster, and Blüthner, to name 3. These makers want no tension in the outer rim and to varying degrees want the rim to actually play an active role in tone production. These may be solid spruce like Bosendorfer, or layered like Bluthner, but they are not bent under great pressure when mating them with the piano. Again I’m open to correction, but Christian Blüthner himself described the layered/sectioned rim of a Blüthner as having “no tension”.
This results, to use Udo Steingraebers analogy, in sound like water on a beach. The gentle waves break softly and evenly across a wide expanse. The result is a tone that emphasizes the fundamental, a more pure (not as in good vs bad) tone.
The alternative is high rim tension, characterized by Steingraeber, some other company whose name I forget, and others. Here a rim made of densely laminated material is bent, under great pressure, into shape. This rim may, when installed, actually squeeze the soundboard to some degree. The result is like a swimming pool, or as Udo says, a harbor. Here the water strikes the hard vertical surfaces of the sides and splashes back, maybe repeatedly. This results in a distinctly different tone that emphasizes higher harmonics.
Steingraeber is proudly a swimming pool piano. Wait, that doesn’t sound quite right. What I mean to say is they look for a more powerful tone that emphasizes higher partials and their construction strives for that result.
Now this brings us to the issue of quantity, specifically the fact that most pianos made today use the high rim tension approach. So, if most makers use it, it must be better, right? It is true that the bent, laminated rim is the most frequently seen production method but I believe it would be a big mistake to say that popularity equals quality. For one thing, bent laminated rims are much cheaper to make. No, not the way Steingraeber approaches it, but yes in the way most low to mid level makers approach it. Because of it’s extreme simplicity (run a bunch of thin sheets through a glue roller, stack them up, put them in a press and wait) it requires far less time and far less skill to make. The attaching of a laminated outer rim to the inner rim also is pretty simple and can hide a world of manufacturing inaccuracy. I’m not saying this is bad since it is important to have pianos available at all price points at at certain price points, certain aspects of manufacturing inaccuracy don’t matter.
Simple sometimes means better, but not always. There are 2 fundamentally different approaches to piano tone available in the world, but the second choice (low rim tension) is really only available at the high (expensive) end. That should tell you something about the cost of that approach.
Which brings me to a recurring theme of mine: isn’t tonal diversity wonderful? You can find anything you want!