[Boatanchors] Headphone Impedance Matching

[Rod Hogg]

I really doubt that they are 'crystal' headphones.  2000 was a common
impedance for headphones for years.
Rod
KØEQH


-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of D C _Mac_
Macdonald
Sent: Wednesday, December 04, 2013 3:27 PM
To: boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] Headphone Impedance Matching

I suspect that crystal headphones suffer from the same temperature and
humidity woes that affect crystal microphones.  I.E., extremely low
tolerance for such. 
* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* Oklahoma City, OK * 
* USAF, Ret (61-81) * 
* * * * * * * * * * * 
 
 
 
> Date: Wed, 4 Dec 2013 12:35:37 -0800
> From: 1oldlens1 at ix.netcom.com
> To: wrcromwell at gmail.com; boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Headphone Impedance Matching
>
> >On 12/04/2013 02:54 PM, D C _Mac_ Macdonald wrote:
> >> I think you can generally expect high impedance phones to work
satisfactorily on low impedance outputs.
> >>
> >> The same is NOT true for low impedance phones on high impedance
outputs.  The low impedance would seriously load down the output.
> >>
> >> * * * * * * * * * * *
> >> * 73 - Mac, K2GKK/5 *
> >> * (Since 30 Nov 53) *
> >> * k2gkk hotmail com *
> >> * Oklahoma City, OK *
> >> * USAF & FAA (Ret.) *
> >> * * * * * * * * * * *
> >> 
> >Hi,
> >
> >Being an old pheart all I have is Hi-Z cans. They make *everything* 
> >sound better - just like the things that go better with Coke. Them young 
> >whipper-snappers don't know what they're missing and too hard headed to 
> >try anything old. More Hi-Z cans for me <evil grin>.
> >
> >73,
> >
> >Bill  KU8H
> 
>     Not sure if this is OT here.  I've measured a lot of old headphones,
impedances vary from around 50 ohms to around 100K ohms.  Modern hi-fi
phones are often made to loundspeaker impedance, i.e. around 8 ohms to
perhsp 30 ohms.  
>     Old type magnetic phones were made to work with crystal radios where
minimum loading was desirable.  The best of them, like the Western Electric
509, have an impedance of around 20K to 25K.  The highest impedance are
Brush crystal phones, typically around 100K for a pair. 
>     The DC resistance is often given and is confused with AC impedance.
Impedance of magnetic type phones is usually about 5 to 7 times the DC
resistance.  Note that many early tube radios were made without audio output
transformers so the DC for the output tube plate goes through the
headphones.  This is where the DC resistance can be important. Its also a
good idea to check very early radios to see if there is DC on the output
terminals. Using an output transformer can be a safety factor. I don't want
to wear any sort of phones with 200 volts going through them. 
>      Low impedance magnetic phones were also made: for instance Trimm made
phones from about 3.2 ohms up to 20K ohms. Western Electric made many types
of phones with impedances from around 50 ohms to around 300 ohms.  
>      WE also made an early moving coil headphone. These were supplied for
motion picture monitoring and for audiology and usually carry a D- spec
number indicating something made by Bell Labs. Usually, moving coils type
phones are specified by _impedance_ rather than DC resistance. 
>      Headphones in pairs are usually connected in series and the
resistance or impedance is that of the pair, not the individual units. An
exception is Brush crystal phones, which are connected in parallel.  The
reason is that that the elements look like low-value capacitors so
connecting in series would not pass low frequencies at all well. BTW, I have
never been able to find a pair of Brush phones that work. In fact out of
several pair I have only one good element. Evidently, the crystal elements
just do not survive well. 
 		 	   		  
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