On the subject of Welte and the music recording method for the
Welte-Mignon reproducing piano, I have developed my own novel theory
of how Welte may have done their dynamic measurements.

It's pretty well accepted among Welte-Mignon buffs that the original
firm in Freiburg had dynamic recording capability, and it worked
surprisingly well.  Exactly how they accomplished what they did is
a mystery that remains an ongoing source of fascination for many of
us in the collecting field.

The following is purely speculative, of course, but it makes more
technical sense than some of the other schemes that have been proposed
and/or rumored over the years.

We can begin by looking at what kind of technology might have been new
and available at the time Edwin Welte began experimenting with dynamic
recording.  The miracle technology of the 1890s was -- what else! --
the telephone.

It's reasonable to suppose that Edwin Welte and associates would have
taken a very serious look at pressure sensors based on the technology
used in carbon microphones.  By the 1890s these had found widespread
application as the microphone in telephone transmitters, and offered
many practical advantages over Alexander Graham Bell's original design.

In basic terms, the carbon transmitter responds to physical pressure,
such as sound waves impinging on an attached diaphragm, by
proportionally changing its internal electrical resistance.

Certainly in that era anyone with a strong technical background would
have read then-current technical journals and would have been aware of
telephone technology.  To the inquiring mind, an extended range of
possibilities would likely have presented itself.

The carbon microphone element is clean, predictable, and capable of
very fast response.  Placing such a device, or a simple variant of it,
under each key or at some critical point in a piano action, could, in
principle, enable the measurement of intensities with which a key was
struck.

Given a bit of applied ingenuity, analog signals from such sensors
could have been plotted automatically to create a crude but usable
dynamic recording of forces.  This application would not have been
used in association with sound waves, but rather in association with
mechanical forces applied to piano keys and their associated parts.

From Welte's perspective, the downside of this was the fact that the
Status: RO

telephone people controlled and jealously guarded patents on carbon
microphones and related devices.  It's well known that there was a
lot of highly charged patent litigation in this area; in the USA, for
example, between Bell and Western Union.  This might tend to explain
the extreme secrecy surrounding the Welte recording process.

It might also explain why so many unlikely (and often technically unsound)
schemes involving carbon rods, pointed wires, and troughs of mercury were
perhaps "leaked" intentionally into the rumor mill to protect legally
risky technology from all external scrutiny.  Edwin Welte never revealed
his secret.

All the best,
Dave Saul
El Cajon, Calif.

P.S.: One further thought.  Those rumors about carbon rods dangling
from springs might have been useful 'way back then for de-fusing any
public speculation that might have arisen from purchases of laboratory
grade carbon for their clandestine activities.