[ARC5] Crystal Headphones

[Richard Knoppow]

    This is an interesting project. Most of the crystal phones 
were made by Brush although there were a few cheap ones made by 
others. The problem with them is that the crystals were evidently 
not sealed well. I have acquired several pair over the last few 
years and found only a single phone that worked. The ones I 
dissected had all turned to mush. You may do better but I suspect 
what I found was typical.
    Crystal phones have the advantage of being extremely high 
impedance, at least 100K per capsule. Unlike magnetic and dynamic 
phones a pair must be connected in parallel. The impedance is 
almost a pure capacitance. They work very well for crystal 
radios, which generally want a minimum load. The best of the 
Brush phones were reasonably flat from perhaps 100Hz to 10 or 
more Khz.
     The old magnetic phones were often 2K DC resistance since 
that was at one time a U.S. Navy specification. However, the AC 
impedance was usually five to 10 times this. For instance the 
familiar Western Electric 509W phones have a DC resistance of 
1100 ohms each but an AC impedance on the order of 12K each or 
typically 24 K per pair since they are usually connected in 
series. This is around the upper limit of the impedance for this 
kind of headphone. Many magnetic phones were made for much lower 
impedance, down to perhaps 50 Ohms per pair where needed for the 
intended application (such as telephone use). Balanced armature 
phones, like the old Baldwin phones, have about the same range of 
impedance. Moving coil phones can be made for about whatever is 
desired but are usually low to medium (600 ohm) impedance. The 
familier military ANBH-1A have voice coils of around 45 ohms but 
have small internal transformers for higher impedance.
    Can't help with the sample, I don't think at this point I 
have any crystal phones that work.

On 9/17/2018 8:41 AM, Fuqua, Bill L wrote:
>    Many years ago, 50's and 60's some company made high impedance 
> crystal headphones, not ear phone but Headphones.
> 
> They were quite sensitive. I am doing a study of headphone and 
> earphone sensitivity and have an assortment of crystal earphones,
> 
> ceramic earphones ( including the ones used lately with crystal 
> radio kits that are terrible) and magnetic headphones (2kOhm) and
> 
> a few odd ones.
> 
>    I have GR calibration source and fixtures and such and am 
> ready to start.
> 
> Today, one can't make a sensitive crystal set due to poor 
> earphones that are available. I plan to try a design of my own 
> after I finish
> 
> the experiment modeled after the old style crystal earphone but 
> using a ceramic cantilever bimorph and foil diaphragm.
> 
> If you have a set of crystal headphones and want to have them 
> compared with the others, please contact me.
> 
> 
> 73
> 
> Bill wa4lav

> 

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL