[rollei_list] Re: OT: Selenium accuracy was: Re: Re: An ebay explanation
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 19 Mar 2007 16:19:16 -0700
----- Original Message -----
From: "Aaron Reece" <oboeaaron@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, March 19, 2007 2:22 PM
Subject: [rollei_list] OT: Selenium accuracy was: Re: Re: An
ebay explanation
On Mar 19, 2007, at 1:42 PM, marcsmall@xxxxxxxxxxx wrote:
It is one of the great myths of photography that selenium
is inherently inaccurate.
Indeed; my all-time favorite application of selenium-cell
technology has to be G.E.'s Pallotrope, an optical
microphone originally designed to record audio onto
motion-picture film. The Brunswick recording company used
it to make several recordings starting in 1925 when they
couldn't get access to the Western Electric electric
recording technology which Victor and Columbia had
licensed.
The Pallotrope worked by suspending a tiny crystal mirror
inside an acoustic recording horn and shining a beam of
light at it; as the sound vibrations shook the mirror,
the reflected light beam was modulated and the resulting
modulation registered on a selenium cell which converted
the fluctuations in light intensity to fluctuations of
voltage. While the audio signals thus produced were
inferior to contemporary electric recordings, there is a
certain evil genius to the concept. I believe Brunswick
shelved the system after a brief time (about a year).
-Aaron
Its really a variation of a device known as a Rayleigh
disc. The Reyleigh disc is used as a first principles method
of measuring the velocity of sound waves in free air. It
consists of a very thin, very light, disc of reflecting
material suspended with threads. A light-beam lever is used
to measure its deviation. By inserting this in a horn the
amount of deviation is increased. I didn't know that
Brunswick had used this. Brunswick electrical recordings
were of quite high quality but those may have been later.
The Western Elecric technology you speak of included
more than microphones. The research division, later to
become Bell Labs, developed an entire electrical recording
system c.1924. This was not adopted by the record industry
to any great extent because most record player of the time
were acoustical and the electrically recorded material did
not make a big difference in audible quality. Essentially
the same system was used by Warner Brothers as the Vitaphone
system for _The Jazz Singer_. This not only put sound movies
on the map but established electrical disc recording in the
record industry.
AT&T/Western electric and General Electric held all of
the vacuum tube patents and most important patents
pertaining to electronic amplification for both audio and
radio frequencies. The two companies created the Radio
Corporation of America, in 1919, to act as a holding agent
for licensing these patents and as a sales agent mostly for
GE. Westinghouse became a partner about a year later. Once
it became evident that sound recording for motion pictures
was profitable the patent licensing dried up. While the RCA
monopoly on patents probably encouraged the development of
radio and, especially broadcasting, it also stiffled
innovation and new manufacturers.
There are several books written about this, one is
_Invention and Innovation in the Radio Industry, another is
_The History of Communication in the United States Navy_. I
will supply more complete citations for these two references
later.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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