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Re: [Amps] power and db

To: Jim Brown <>, AMPS <>
Subject: Re: [Amps] power and db
From: Dave <>
Date: Wed, 4 Feb 2009 22:28:33 +0000
List-post: <">>
Maybe that's what he meant.  As you know, the Great Man had a mischievous mind 
as well as well as a brilliant one.  He certainly seems to have had more of a 
sense of humour than most academics I worked with. Maybe he meant that we never 
quite know all the theory.  Maybe like you say he never said it...


-----Original Message-----
From: Jim Brown <>
Sent: 04 February 2009 21:06
To: AMPS <>
Subject: Re: [Amps] power and db

On Wed, 4 Feb 2009 20:31:46 +0000 (GMT), DAVE WHITE wrote:

>However - in a quote I believe was atttributed to a certain Prof. 
>A. Einstein - "In theory, theory and practice are the same thing.- 
>In practice they're not."

I recently finished reading a bio of Einstein, and I doubt that he 
would have said exactly that. 

I have a different philosophy. The real world is complicated, and 
real problems often consist of many elements. If you think there's a 
difference between theory and practice, you don't know enough theory 
to understand the many things that are actually going on. In other 
words, you're looking at the elephant through too small a hole in the 

>In practice I'm sure that the human ear can discern a couple of dB 
>if the signal is marginal.-  

Absolutely. The study of human perception of sound is called 
psychoacoustics, and it has been a well developed science for much of 
the last century. When the engineers at Bell Labs were inventing 
stereo in the 1930's, they made use of psychoacoustic work that had 
been published around 1850 by Joseph Henry (the same guy whose name 
is on the unit of inductance, in tribute to his invention of some 
motors and meters), and further study based on his work by 
psychoacoustic people at Harvard around 1935!  I'm told that Lord 
Rayleigh, the great British scientist who was a contemporary of 
Henry's also published work on psychoacoustics similar to Henry's, 
but I haven't found it yet. 

When two sounds are nearly equal in loudness, a change of only a dB 
or two in one of them relative to the other makes a significant 
difference in how we hear them. This is WELL KNOWN to those who have 
bothered to learn the science. That's not a difference between theory 
and practice, it's a difference between knowledge and ignorance of 
well established science! 

>In theory this would be nonsense but 
>it seems to hold true for me particularly on 160m.

See my previous post in this thread. 

Jim Brown
Audio Systems Group, Inc.
Member Acoustical Society of America

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