[VoIP] WE Earpiece impedance?

[Donald Froula]

Thanks! Now that I know the capsule is a "U1" model, I
Googled and found an ARRL construction article that
uses the U1 in a crystal radio circuit. Quite nice, as
it uses a MOSFET as a detector instead of a germanium
diode!

http://www.arrl.org/qst/2007/01/culter.pdf

Anyway, this is from the article:

"I have used an audio signal generator and RadioShack
sound level meter to measure the sensitivity of
telephone receiver elements such as the GTE D-51030A
or Western Electric U-1 or LB-1, which can be obtained
from old telephones in thrift shops for several
dollars. The sensitivity is about 122 dB SPL/mW or 14
dB better than stereo headphones, although the
response is limited to about 3 kHz. If we assume an
earphone aperture of 1 cm², this is an efficiency of
16% in converting electrical power to sound power. The
Knowles Acoustics CM-3152 balanced-armature element
should offer similar performance.7 All of these
elements have an impedance of 150 Ù at 1 kHz."

So, you seem to have remembered correctly!

Best,

Don


--- Dennis D Hock <hockd at dteenergy.com> wrote:

> I am pretty sure it is 135 ohms for a std U1. 
> Please feel free to refresh my memory.
>  
> Thanks,
>  
> Dennis Hock
> 
> -----voip-bounces at ckts.info wrote: -----
> 
> 
> To: voip at ckts.info
> From: Donald Froula <dfroula at sbcglobal.net>
> Sent by: voip-bounces at ckts.info
> Date: 04/23/2008 03:12PM
> Subject: [VoIP] WE Earpiece impedance?
> 
> Would anyone know the nominal impedance of the
> earpiece from a handset from an old Western Electric
> "500" desk set? I can't seem to find the info on any
> of my schematics or by Google.
> 
> Thanks,
> 
> Don
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