[ARC5] Headphones H-43 B/U

[Richard Knoppow]

----- Original Message ----- 
From: "Dennis Monticelli" <dennis.monticelli at gmail.com>
To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
Cc: "Kenneth G Gordon" <kgordon2006 at frontier.com>; "ARC-5 
Maillist" <ARC5 at mailman.qth.net>
Sent: Tuesday, March 25, 2014 9:31 PM
Subject: Re: [ARC5] Headphones H-43 B/U


> Richard,
>
> From a standpoint of power sensitivity, which are the best 
> of the
> headphones?  I heard that the Baldwins are very sensitive.
>
> Dennis AE6C
>
>
    That is a question I can't answer. The problem is that 
one would have to measure the sound output of the headphone 
with a known amount of power. The way this is done formally, 
lets say to calibrate the headphones used for audiometers is 
to use a headphone coupler or artificial ear that works with 
a calibrated microphone. I just don't have the means to do 
it. However, I am being a bit academic. Baldwin phones are 
indeed quite sensitive, they also have quite high impedance. 
The two I have come out somewhere above 20K at one Khz. They 
are also pretty loud. But I am not sure they are louder than 
say Western Electric 509 phones.  Brush crystal phones are 
also very sensitive but, as I hinted before, finding a pair 
that works is difficult.  Crystal headphones and microphones 
are very sensitive to high temperatures and high humidity. 
The makers try to seal them as best they can against 
moisture but the couple I dissected had turned to mush 
inside. If you want good phones for a crystal radio choose 
the highest impedance you can find. However, most magnetic 
phones are strongly resonant so the audio quality is not so 
good. The Brush phones, when they work, have the advantage 
of having flat frequency response and quite good fidelity. 
Trimm also made some very high impedance phones under the 
"Featherweight" name. These came in about a dozen impedances 
but the amateur radio specials were 24 Kohms. I have a 
couple of pair and they do meet this spec.
     FWIW, Baldwin used a balanced armature motor. This is a 
U magnet with the voice coil wound around the magnet. The 
moving element is a reed armature clamped at the bottom of 
the U. The reed moves sideways between the poles of the U 
magnet. The free end is fastened to a short rod that couples 
to the center of a diaphragm made of mica. I am not sure why 
Baldwin choose mica but it may have been the best material 
available at the time since there were no plastics and the 
mica would have been lighter than a metal diaphragm. 
Nathenial Baldwin submitted his design to the U.S.Navy in 
the spark days.  They accepted it and helped him to produce 
them. He built the original models in his kitchen. Baldwin 
eventually got a patent but would not accept royalties from 
the navy. This is detailed in _A History of 
Communication-Electronics in the United States Navy_ Capt. 
Linwood S. Howeth.  The book is not hard to find used and is 
on line in PDF form free. This is a fascinating history for 
anyone interested in the early development of wireless and 
the formation of RCA.


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