[TMC] Why GPR-90s Look So Good

[Richard Knoppow]

----- Original Message ----- 
From: "Woody Demitz" <wdemitz at verizon.net>
To: "John Poulton" <jp at cs.unc.edu>
Cc: "tmc collector's group" <TMC at mailman.qth.net>
Sent: Friday, December 12, 2014 8:38 AM
Subject: Re: [TMC] Why GPR-90s Look So Good


> Thanks, John.  I viewed the jpg of the GPR-90's front 
> panel and tried various measurements.  As my research 
> model, I chose "Vern" the snaggle-toothed muffler repair 
> guy in the Aamco TV commercial of years ago, who grins 
> compellingly at the potential customer and says, "We don't 
> have your exact muffler, but we''ll make it fit." 
> Methodology: hold metal tape measure up to IPad screen and 
> try to avoid scratching screen, while taking rough reading 
> of various potential golden rectangles on panel. Result: 
> Utter failure, until I decided to work the problem. 
> Instead of using L=width of the inset holding the freq 
> dials and H=distance from bottom of the two tuning knobs 
> to top of inset, which yielded a disappointing 1.4:1 
> ratio, I redefined "H" to begin not from the bottom of the 
> freq tuning knobs, but--and this is brilliant--from the 
> CENTER of those knobs. My theory being that the human eye 
> is drawn not to the outside rim of those knobs, but to 
> their center. This yielded a much more sa
> tisfying ratio of 1.68.  Not quite the perfect 1.618, but 
> hey..
>
> 73,
> Woody KO3S

     The design philosophy being discussed here is called 
"Dynamic Symmetry" and was mostly the invention of a fellow 
named Jay Hambridge. It was popular in the period from about 
the late 'teens through perhaps the 1950s. The theory was 
disproved early on but the method does frequently result in 
eye pleasing dimensions.  Several industrial designers of 
the period used Dynamic Symmetry in their work, notably John 
Vassos, who did a lot of design for RCA.
For Hambridge see:
http://en.wikipedia.org/wiki/Jay_Hambidge

     One of RCA's acoustical designers, Michael Rettinger, 
used Dynamic Symmetry as an element in the acoustical design 
of sound studios.

    A web search for "Dynamic Symmetry" will get a lot of 
hits.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com