[ARC5] Crystal Headphones

[Dennis Monticelli]

More modern magnetic phones (still of the old style) can be quite good.

I have a NIB set of H-43B/U headphones (datecode 1990) that were made for
Geiger counters.  I measured an impedance of 21K at 1KHz so I presume the
transducers are 10K wired in series.  These cans produce plainly audible
tones with only 1mV rms.  That equates to 50 picowatts!  Impressive
sensitivity and high enough Z for crystal radios.

Dennis AE6C

On Tue, Sep 18, 2018 at 11:12 AM, Richard Knoppow <1oldlens1 at ix.netcom.com>
wrote:

>    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
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