[ARC5] Crystal Headphones

[Richard Knoppow]

    First of all good luck with the back surgery. From your 
background I am sure you have investigated it thoroughly. I am a 
sufferer from back problems which have disabled me. I will be 
interested in knowing how your surgery works out. I am reluctant 
about having back surgery and my doctor is not enthusiastic.

    I was writing with the assumption that most readers did not 
have much background in physics or acoustics. You are way ahead 
of the game. I will be interested in what you find out.
    The sound powered phones I have are handsets, I don't 
remember the type number but two were made for the Navy and one 
seems to be a commercial version. They do not have talk switches. 
I think the talk switch was mainly to cut out background noise.
    All three are from different makers, one is RCA, one is 
Automatic Electric and the other a company I never heard of but 
its different and does not work with the others. The RCA and AE 
sets both have a DC resistance of 35 ohms. Receiver and 
transmitter are of different designs.
     Its possible to use any sort of generating transducer as a 
sound powered phone. Two magnetic headphones will work although 
they are not very loud. You can short the sleeve to the tip or 
the two tips together and talk into one and hear it in the other.
     I do not have a ceramic headphone or, for that matter, a 
microphone.  Ceramic mics and phono pickups began to replace 
crystal ones some time around 1950. They have considerably lower 
output but are much more rugged, far less sensitive to heat and 
moisture. The difference in level between the Astatic D-104 and 
the ceramic version the C-104 is nearly 10 db.
     Unfortunately, the paper you linked to is only an abstract. 
The AIP does not offer free downloads to non-members. I used to 
be a member of the Acoustical Society but dropped out some years 
ago.
On 9/18/2018 11:12 PM, Fuqua, Bill L wrote:
>     Sorry that I have not been able to reply or even check email 
> since Monday.
> 
> Having back surgery Thursday and will be out of commission for a 
> while and been
> 
> distracted by other stuff.
> 
>    I have a sound pressure meter (inexpensive Chinese version) 
> and a GR sound pressure
> 
> calibrator. The sound pressure (level) meter was within 1.5db 
> which I found amazing.
> 
> I have built a fixture to  that has one port for the sound level 
> meter and two for sources
> 
> such as earphones and calibrator. So I can easily compare two 
> types of earphones or
> 
> one earphone and calibrator.
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL