[ARC5] Crystal Headphones
Brooke Clarke
brooke at pacific.net
Wed Sep 19 17:01:03 EDT 2018
Hi Bill:
The Remco toy phones I opened have classical electromagnetic sound powered elements:
https://www.prc68.com/I/SoundPoweredTelephone.html#Remco_Toy
Note: Click on photo for larger version, if cursor is (+) click again.
PS note that there is only one element positioned in the microphone compartment. It also works as the receiver.
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
https://www.end2partygovernment.com/2012Issues.html
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
>
> I was referring to the toy REMCO sound powered phones that did not work over a long
>
> distance, thus not so much shunt capacitance. I recall similar phones used with some of their
>
> radio kits. However, I do have some and plan to check them as well. I took alot of these
>
> apart as a child to see what made them tick.
>
> 73
>
> Bill wa4lav
>
>
>
>
> ------------------------------------------------------------------------------------------------------------------------
> *From:* arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> on behalf of Richard Knoppow <1oldlens1 at ix.netcom.com>
> *Sent:* Tuesday, September 18, 2018 10:43 PM
> *To:* arc5 at mailman.qth.net
> *Subject:* Re: [ARC5] Crystal Headphones
> I've written a little about this. I think most sound powered
> phones are relatively low in impedance, not desirable for crystal
> set radios. However, perhaps they work well anyway.
> The problem with quoting this stuff is that I am responding
> mostly to specific questions and don't want to be boring so tend
> to simplify a bit. However, I have no objection to using my
> stuff, with attribution. I make no claim to being an expert. My
> knowledge, such as it is, is the result of plain old curiosity
> and having the privilege of knowing some real experts who were
> willing to teach me.
>
> On 9/18/2018 3:34 PM, kn7sfz wrote:
> > Hi Richard,
> >
> > Where do the 'sound powered' headphones fit on your chart. I
> > have heard they're pretty good for xtal sets.
> >
> > Thanks,
> >
> > Richard kn7sfz in Orygun
> >
> >
> >
> > On 9/18/2018 2:33 PM, Richard Knoppow wrote:
> >> One must be careful not to confuse sensitivity with the
> >> impedance. Sensitivity is a power measurement, that is
> >> electrical power in to acoustical power out. It is possible to
> >> have high impedance but low power sensitivity although I can't
> >> give you an example of a commercial headphone. High impedance
> >> is desirable for sources that are high impedance such as
> >> crystal sets and AC impedance bridges. However, where the
> >> source is low or medium impedance headphones with matching
> >> impedance will be louder than the high impedance phones.
> >> Testing for sensitivity requires a calibrated artificial ear if
> >> the results are to have any accuracy. These are rare. However,
> >> one can test with just your ears or a sound level meter with
> >> the microphone held against the headphone. An interesting
> >> experiment is to take an oscillator and feed various headphones
> >> from it through a very high value resistor, preferably at least
> >> five times the expected headphone impedance. 100K is enough
> >> although more is better. Just connect the phones and see which
> >> is the loudest. Usually, it will be the ones with the highest
> >> impedance but some with the same impedance will differ. In some
> >> cases a lower impedance phone will be louder than a higher
> >> impedance one. The difference is probably in the magnet
> >> strength but can also be due to differences in the diaphragm
> >> spacing from the pole pieces.
> >> The loudest phones I have are: Western Electric 509W, WE
> >> Signal Corps P-11, Baldwin Type C. However, if you make the
> >> same test using a low impedance source, say 500 ohms, the
> >> results will be different. For instance WE type 528 (600 ohm)
> >> will be louder than the WE 509W. WE and Trimm made magnetic
> >> phones down to about 50 ohms per pair. For the same reason you
> >> may find modern high-fidelity moving coil phones too loud when
> >> connected to a receiver where they are across the loudspeaker
> >> output. Typically, this will be 4 to 8 ohms and most of these
> >> phones are are around 50 ohms impedance. The receivers will
> >> often specify 500 ohms although 20K phones usually work just
> >> fine and are of reasonable loudness.
> >> Measuring efficiency is a matter of measuring power out to
> >> power in. That requires an impedance match on the electrical
> >> side and, for best power efficiency, also on the acoustical side.
> >> Most of the magnetic type phones have a strong resonance,
> >> typically in the vicinity of 1Khz. While some attempt was made
> >> to broaden out the resonance (such as using a salt shaker type
> >> cap) the difference is not great. It is possible to make quite
> >> non resonant magnetic phones but they become complex. The best
> >> example is the Western Electric type HA-2 designed for the
> >> series 500 telephone. These are described in great detail in
> >> the Bell System Technical Journal and elsewhere by Mott and
> >> Miner of Bell Labs who designed it. There are other types that
> >> fall broadly in the "magnetic" category, such as the balanced
> >> armature type as typified by the Baldwin phones with mica
> >> diaphragms and also used in some sound-powered phones.
> >> While one can find oodles of information about moving coil
> >> speakers and microphones in the technical literature of the
> >> last century there is not much about the plain magnetic phones
> >> although they were made by many different companies. Frustrating.
> >> FWIW, the highest impedance phones magnetic phones I've
> >> measured are the WE SC type P-11 (close to 30K), others were
> >> the WE 509W (25K), Trimm Featherweight (24K) but the
> >> Featherweights are not as loud on a very high impedance source
> >> as the WE phones or as the Trimm Commercial phones which
> >> measure only 17K (advertised value).
> >> Measurements were made on: General Radio 650A bridge with
> >> external null detector, GR 1650A, GR Z-Y bridge, all at 1K
> >> Note also that magnetic phones are mostly inductive so the
> >> impedance varies with the frequency. I measure at 1K. I found
> >> the advertised values of Trimm phones are high at 1K but about
> >> right at 1200 Hz. However, the resonance is at about 1K. I
> >> tried to measure the motional impedance of a couple of phones
> >> but gave it up because I can't separate it from the overall
> >> impedance. i.e., you can't see a resonant rise in the impedance.
> >> Enough, I am glad at least one or two people find this of
> >> some interest.
> >> On 9/18/2018 1:35 PM, Dennis Monticelli wrote:
> >>> 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
> >>
> >
> >
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> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
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